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Document and Entity Information	12 Months Ended
Document and Entity Information	Dec. 31, 2017 shares
Document And Entity Information [Abstract]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	ZLAB
Entity Registrant Name	Zai Lab Ltd
Entity Central Index Key	0001704292
Entity Common Stock, Shares Outstanding	50,555,903
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer

Consolidated Balance Sheets - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 229,660,148	$ 83,948,770
Prepayments and other current assets	954,506	143,527
Total current assets	230,614,654	84,092,297
Investments in equity investees	1,650,348	500,000
Prepayments for equipment	126,411	1,417,029
Property and equipment	11,853,764	1,246,058
Intangible assets	20,089	7,000
Long term deposits	306,825	267,980
Value added tax recoverable	5,062,137	1,376,921
Total assets	249,634,228	88,907,285
Current liabilities:
Accounts payable	8,967,685	523,338
Warrant liabilities		3,900,000
Other payables	3,101,459	750,118
Total current liabilities	12,069,144	5,173,456
Deferred income	2,394,124	778,434
Total liabilities	14,463,268	5,951,890
Commitments and contingencies (Note 16)
Mezzanine equity
Total mezzanine equity		134,507,144
Shareholders' (deficit) equity
Ordinary shares (par value of US$0.00006 per share; 83,333,333 shares authorized, 9,657,175 and 49,912,570 shares issued and outstanding as of December 31,2016 and 2017, respectively)	2,995	579
Subscription receivable	(18)	(5)
Additional paid-in capital	345,269,688	9,313,646
Accumulated deficit	(110,551,613)	(60,167,437)
Accumulated other comprehensive (loss) income	449,908	(698,532)
Total shareholders' (deficit) equity	235,170,960	(51,551,749)
Total liabilities, mezzanine equity and shareholders' (deficit) equity	$ 249,634,228	88,907,285
Series A1 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		10,028,572
Series A2 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		18,278,572
Series B1 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		53,100,000
Series B2 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		$ 53,100,000

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Ordinary shares, par value	$ 0.00006	$ 0.00006
Ordinary shares, shares authorized	83,333,333	83,333,333
Ordinary shares, shares issued	49,912,570	9,657,175
Ordinary shares, shares outstanding	49,912,570	9,657,175
Series A1 Convertible Preferred Shares
Convertible preferred shares, par value		$ 0.00006
Convertible preferred shares, shares authorized		8,466,667
Convertible preferred shares, shares issued		8,466,665
Convertible preferred shares, shares outstanding		8,466,665
Series A2 Convertible Preferred Shares
Convertible preferred shares, par value		$ 0.00006
Convertible preferred shares, shares authorized		8,904,032
Convertible preferred shares, shares issued		8,442,221
Convertible preferred shares, shares outstanding		8,442,221
Series B1 Convertible Preferred Shares
Convertible preferred shares, par value		$ 0.00006
Convertible preferred shares, shares authorized		5,562,337
Convertible preferred shares, shares issued		5,562,335
Convertible preferred shares, shares outstanding		5,562,335
Series B2 Convertible Preferred Shares
Convertible preferred shares, par value		$ 0.00006
Convertible preferred shares, shares authorized		3,973,098
Convertible preferred shares, shares issued		3,973,096
Convertible preferred shares, shares outstanding		3,973,096

Consolidated Statements of Operations - USD ($)	12 Months Ended
Consolidated Statements of Operations - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ (39,341,518)	$ (32,149,157)	$ (13,587,145)
General and administrative	(12,049,518)	(6,380,144)	(2,762,292)
Loss from operations	(51,391,036)	(38,529,301)	(16,349,437)
Interest income	527,351	403,266	5,005
Changes in fair value of warrants	200,000	(1,920,000)	(1,980,000)
Other income	933,158	2,533,966	341,112
Other expense	(403,997)	(143)	(38,417)
Loss before income tax and share of loss from equity method investment	(50,134,524)	(37,512,212)	(18,021,737)
Income tax expense	0
Share of loss from equity method investment	(249,652)
Net loss	(50,384,176)	(37,512,212)	(18,021,737)
Net loss attributable to ordinary shareholders	$ (50,384,176)	$ (37,512,212)	$ (18,021,737)
Loss per share - basic and diluted	$ (2.32)	$ (3.97)	$ (2.07)
Weighted-average shares used in calculating net loss per ordinary share - basic and diluted	21,752,757	9,439,028	8,693,655

Consolidated Statements of Comprehensive Loss - USD ($)	12 Months Ended
Consolidated Statements of Comprehensive Loss - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (50,384,176)	$ (37,512,212)	$ (18,021,737)
Other comprehensive (loss) income, net of tax of nil:
Foreign currency translation adjustments	1,148,440	(594,912)	(98,893)
Comprehensive loss	$ (49,235,736)	$ (38,107,124)	$ (18,120,630)

Consolidated Statements of Comprehensive Loss (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Other comprehensive (loss) income, tax	$ 0	$ 0	$ 0

Consolidated Statements of Shareholders' (deficit) Equity - USD ($)	Total	Ordinary Shares	Additional Paid In Capital	Subscription Receivable	Accumulated Deficit	Accumulated Other Comprehensive Loss
Balance at Dec. 31, 2014	$ (2,950,677)	$ 490	$ 1,687,048		$ (4,633,488)	$ (4,727)
Balance, Shares at Dec. 31, 2014		8,166,666
Issuance of ordinary shares upon vesting of restricted shares		$ 43	(42)	$ (1)
Issuance of ordinary shares upon vesting of restricted shares, Shares		718,518
Share-based compensation	2,701,404		2,701,404
Net loss	(18,021,737)				(18,021,737)
Foreign currency translation adjustments	(98,893)					(98,893)
Balance at Dec. 31, 2015	(18,369,903)	$ 533	4,388,410	(1)	(22,655,225)	(103,620)
Balance, Shares at Dec. 31, 2015		8,885,184
Issuance of ordinary shares upon vesting of restricted shares		$ 46	(42)	(4)
Issuance of ordinary shares upon vesting of restricted shares, Shares		771,991
Share-based compensation	4,925,278		4,925,278
Net loss	(37,512,212)				(37,512,212)
Foreign currency translation adjustments	(594,912)					(594,912)
Balance at Dec. 31, 2016	$ (51,551,749)	$ 579	9,313,646	(5)	(60,167,437)	(698,532)
Balance, Shares at Dec. 31, 2016	9,657,175	9,657,175
Issuance of ordinary shares upon vesting of restricted shares		$ 100	(87)	(13)
Issuance of ordinary shares upon vesting of restricted shares, Shares		1,666,145
Exercise of shares option	$ 65,500	$ 6	65,494
Exercise of shares option, Shares	100,834	100,834
Exercise of warrant	$ 4,700,000	$ 28	4,699,972
Exercise of warrant, Shares		461,808
Conversion of convertible preferred shares to ordinary shares	163,607,144	$ 1,707	163,605,437
Conversion of convertible preferred shares to ordinary shares, Shares		28,443,275
Issuance of ordinary shares upon initial public offering, net of issuance cost	157,654,695	$ 575	157,654,120
Issuance of ordinary shares upon initial public offering, Shares		9,583,333
Share-based compensation	9,931,106		9,931,106
Net loss	(50,384,176)				(50,384,176)
Foreign currency translation adjustments	1,148,440					1,148,440
Balance at Dec. 31, 2017	$ 235,170,960	$ 2,995	$ 345,269,688	$ (18)	$ (110,551,613)	$ 449,908
Balance, Shares at Dec. 31, 2017	49,912,570	49,912,570

Consolidated Statements of Shareholders' (deficit) Equity (Parenthetical)	12 Months Ended
	Dec. 31, 2017 USD ($)
Statement Of Stockholders Equity [Abstract]
Share issuance cost upon initial public offering	$ 2,770,299

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (50,384,176)	$ (37,512,212)	$ (18,021,737)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation of property and equipment	545,705	198,224	125,774
Amortization of intangible assets	2,422	781	733
Share-based compensation	9,931,106	4,925,278	2,701,404
Share of loss from equity method investment	249,652
Loss on disposal of property and equipment	12,961		38,417
Change in fair value of warrants	(200,000)	1,920,000	1,980,000
Changes in operating assets and liabilities:
Prepayments and other current assets	(810,979)	(74,507)	33,713
Long term deposits	(38,845)	(267,980)
Value added tax recoverable	(3,685,216)	(1,376,921)
Accounts payable	8,444,347	(929,716)	1,287,687
Other payables	1,950,152	242,187	327,500
Deferred income	1,615,690	716,835	61,599
Net cash used in operating activities	(32,367,181)	(32,158,031)	(11,464,910)
Cash flows from investing activities:
Purchase of cost method investment		(500,000)
Disposal of cost method investment	500,000
Purchase of equity method investment	(1,900,000)
Purchase of property and equipment	(9,102,330)	(2,223,882)	(738,470)
Disposal of property and equipment	82,789
Purchase of intangible assets	(14,690)	(5,615)
Net cash used in investing activities	(10,434,231)	(2,729,497)	(738,470)
Cash flows from financing activities:
Proceed from issuance of convertible preferred shares, net of issuance cost	29,100,000	106,200,000	18,278,572
Proceeds from exercise of warrants	1,000,000
Proceeds from exercises of stock options	65,500
Proceeds from issuance of ordinary shares upon initial public offering	160,424,994
Payment of initial public offering costs	(2,730,299)
Net cash provided by financing activities	187,860,195	106,200,000	18,278,572
Effect of foreign exchange rate changes on cash and cash equivalents	652,595	(524,398)	(66,770)
Net increases in cash and cash equivalents	145,711,378	70,788,074	6,008,422
Cash and cash equivalents - beginning of the year	83,948,770	13,160,696	7,152,274
Cash and cash equivalents - end of the year	229,660,148	$ 83,948,770	$ 13,160,696
Supplemental disclosure on non-cash investing and financing activities:
Payables for purchase of property and equipment	413,657
Payables for initial public offering costs	40,000
Conversion of convertible preferred shares	163,607,144
Exercise of warrants	$ 3,700,000

Organization and Principal Activities

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Principal Activities

1.	Organization and principal activities

Zai Lab Limited (the “Company”) was incorporated on March 28, 2013 in the Cayman Islands as an exempted company with limited liability under the Companies Law of the Cayman Islands. The Company and its subsidiaries (collectively referred to as the “Group”) are principally engaged in discovering or licensing, developing and commercializing proprietary therapeutics that address areas of large unmet medical needs in the China market, including in the fields of oncology, autoimmune and infectious disease therapies.

As of December 31, 2017, the Group's significant operating subsidiaries are as follows:

Name of company	Place of incorporation	Date of incorporation	Percentage of ownership	Principal activities
Zai Lab (Hong Kong) Limited	Hong Kong	April 29, 2013	100%	Operating company for business development and R&D activities
Zai Lab (Shanghai) Co., Ltd.	The People's Republic of China ("PRC" or "China")	January 6, 2014	100%	Development and commercialisation of innovative medicines
Zai Lab (AUST) Pty., Ltd.	Australia	December 10, 2014	100%	Clinical trial activities
Zai Lab (Suzhou) Co., Ltd.	PRC	November 30, 2015	100%	Development and commercialisation of innovative medicines
Zai Biopharmaceutical (Suzhou) Co., Ltd.	PRC	June 15, 2017	100%	Development and commercialisation of innovative medicines

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of significant accounting policies

2.	Summary of significant accounting policies

(a) Basis of presentation

The consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP").

(b) Principles of consolidation

The consolidated financial statements include the financial statements of the Company and its subsidiaries. All intercompany transactions and balances among the Group and its subsidiaries are eliminated upon consolidation.

The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the period. Areas where management uses subjective judgment include estimating the useful lives of long-lived assets, assessing the impairment of long-lived assets, valuation of ordinary shares, share-based compensation expenses, recoverability of deferred tax assets and the fair value of the financial instruments. Management bases the estimates on historical experience and various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results could differ from these estimates.

(d) Foreign currency translation

The functional currency of Zai Lab Limited and Zai Lab (Hong Kong) Limited are the United States dollar ("$"). The Group's PRC subsidiaries determined their functional currency to be Chinese Renminbi ("RMB"). The Group's Australia subsidiary determined its functional currency to be Australia dollar ("A$"). The determination of the respective functional currency is based on the criteria of Accounting Standard Codification ("ASC") 830, Foreign Currency Matters. The Group uses the United States dollar as its reporting currency.

Assets and liabilities are translated from each entity's functional currency to the reporting currency at the exchange rate on the balance sheet date. Equity amounts are translated at historical exchange rates, and expenses, gains and losses are translated using the average rate for the year. Translation adjustments are reported as cumulative translation adjustments and are shown as a separate component of other comprehensive loss in the consolidated statements of changes in shareholders' deficits and comprehensive loss.

Monetary assets and liabilities denominated in currencies other than the applicable functional currencies are translated into the functional currencies at the prevailing rates of exchange at the balance sheet date. Nonmonetary assets and liabilities are remeasured into the applicable functional currencies at historical exchange rates. Transactions in currencies other than the applicable functional currencies during the year are converted into the functional currencies at the applicable rates of exchange prevailing at the transaction dates. Transaction gains and losses are recognized in the consolidated statements of operations.

(e) Cash and cash equivalents

The Group considers all highly liquid investments purchased with original maturities of three months or less to be cash equivalents. Cash and cash equivalents consist primarily of cash on hand, demand deposits and highly liquid investments with maturity of less than three months and are stated at cost plus interests earned, which approximates fair value.

(f) Investments in equity investees

The Group uses the equity method to account for an equity investment over which it has significant influence but does not own a majority equity interest or otherwise control. The Group records equity method adjustments in share of earnings and losses. Equity method adjustments include the Group’s proportionate share of investee income or loss, adjustments to recognize certain differences between the Group’s carrying value and its equity in net assets of the investee at the date of investment, impairments, and other adjustments required by the equity method. Dividends received are recorded as a reduction of carrying amount of the investment. Cumulative distributions that do not exceed the Group’s cumulative equity in earnings of the investee are considered as a return on investment and classified as cash inflows from operating activities. Cumulative distributions in excess of the Group’s cumulative equity in the investee’s earnings are considered as a return of investment and classified as cash inflows from investing activities.

For equity investments over which the Group does not have significant influence or control, the cost method of accounting is used. Under the cost method, the Group carries the investment at cost and recognizes income to the extent of dividends received from the distribution of the equity investee’s post-acquisition profits.

The Group is required to perform an impairment assessment of its investments whenever events or changes in business circumstances indicate that the carrying value of the investment may not be fully recoverable. An impairment loss is recorded when there has been a loss in value of the investment that is other than temporary. No impairment was recorded for the years ended December 31, 2015, 2016 and 2017.

(g) Prepayments for equipment

The prepayments for equipment purchase are recorded in long term prepayments considering the prepayments are all related to property and equipment.

(h) Property and equipment

Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets as follows:

		Useful life
Office equipment		3 years
Electronic equipment		3 years
Vehicle		4 years
Laboratory equipment		5 years
Manufacturing equipment		10 years
Leasehold improvements		lesser of useful life or lease term

Construction in progress represents property and equipment under construction and pending installation and is stated at cost less impairment losses if any.

(i) Long term deposits

Long term deposits represent amounts paid in connection with the Group’s long-term lease agreements.

(j) Value added tax recoverable

Value added tax recoverable represent amounts paid by the Group for purchases. The amounts were recorded as long-term assets considering they are expected to be deducted from future value added tax payables arising on the Group's revenues which it expects to generate in the future.

(k) Intangible assets

Intangible assets mainly consist of externally purchased software which are amortized over five years on a straight-line basis. As of December 31, 2016 and 2017, the original value of the Group's intangible assets is $8,684 and $24,377 with accumulated amortization of $1,684 and $4,288.

(l) Impairment of long-lived assets

Long-lived assets are reviewed for impairment in accordance with authoritative guidance for impairment or disposal of long-lived assets. Long-lived assets are reviewed for events or changes in circumstances, which indicate that their carrying value may not be recoverable. Long-lived assets are reported at the lower of carrying amount or fair value less cost to sell. For the years ended December 31, 2015, 2016 and 2017, there was no impairment of the value of the Group's long-lived assets.

(m) Fair value measurements

The Group applies ASC topic 820 ("ASC 820"), Fair Value Measurements and Disclosures, in measuring fair value. ASC 820 defines fair value, establishes a framework for measuring fair value and requires disclosures to be provided on fair value measurement.

ASC 820 establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1 - Observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets.

Level 2 - Include other inputs that are directly or indirectly observable in the marketplace.

Level 3 - Unobservable inputs which are supported by little or no market activity.

ASC 820 describes three main approaches to measuring the fair value of assets and liabilities: (1) market approach; (2) income approach and (3) cost approach. The market approach uses prices and other relevant information generated from market transactions involving identical or comparable assets or liabilities. The income approach uses valuation techniques to convert future amounts to a single present value amount. The measurement is based on the value indicated by current market expectations about those future amounts. The cost approach is based on the amount that would currently be required to replace an asset.

Financial instruments of the Group primarily include cash and cash equivalents, prepayments and other current assets, accounts payable, warrant liabilities and other payables. As of December 31, 2016 and 2017, the carrying values of cash and cash equivalents, prepayments and other current assets, accounts payable and other payable approximated their fair values due to the short-term maturity of these instruments. As of December 31, 2016, the warrant liabilities were recorded at fair value as determined on the respective issuance dates and subsequently adjusted to the fair value at reporting date. During the year ended December 31, 2017, the warrants were exercised to purchase 461,808 Series A2 convertible preferred shares. The Group determined the fair values of the warrant liabilities with the assistance of an independent third-party valuation firm.

Liabilities measured at fair value on a recurring basis as of December 31, 2016 are summarized below:

	Level 1		Level 2		Level 3
	$		$		$
Warrant liabilities		—		—		3,900,000

The Group has measured the warrant liabilities at fair values on a recurring basis using significant unobservable inputs (Level 3) as of the years ended December 31, 2016.

The Group used the binomial model to estimate the fair value of warrant liabilities using the following assumptions:

	December 31, 2016
Risk-free rate of return		2.9	%
Vesting date	April 1, 2016
Maturity date	December 31, 2021
Estimated volatility rate		70	%
Exercise price		2.16
Fair value of underlying preferred shares		9.84

The model requires the input of highly subjective assumptions including the risk-free rate of return, expected vesting date, maturity date, estimated volatility rate and fair value of underlying preferred share's price. The risk-free rate for periods within the contractual life is based on the US treasury bonds with maturity similar to the maturity of the warrants as of valuation dates plus a China country risk premium. On April 1, 2016, the investment amount met the $7,000,000 threshold, therefore, the vesting date was on April 1, 2016. For maturity date, the terms state that it shall be the earlier of 6 years from grant and 90 days before the initial public offering (“IPO”) date. Prior to 2017, the Group did not have a concrete plan to undertake an IPO, and as such, the maturity date was estimated to be December 31, 2021. For expected volatilities, the Group has made reference to the historical price volatilities of ordinary shares of several comparable companies in the same industry as the Group. The estimated fair value of the preferred shares was determined with assistance from an independent third-party valuation firm. The Group's management is ultimately responsible for the determination of the estimated fair value of its preferred shares.

The significant unobservable inputs used in the fair value measurement of the warrant liabilities include risk-free rate of return, interval between vesting date and maturity date, estimated volatility rate and fair value of underlying preferred shares. Significant decreases in interval between vesting date and maturity date, estimated volatility rate and fair value of underlying preferred shares would result in a significantly lower fair value measurement. Significant increases in risk-free rate of return would result in a significantly lower fair value measurement.

(n) Revenue recognition

The Group has not yet generated any revenues from the sale of goods or from the rendering of services.

Prior to the adoption of ASC 606, the Group will recognize any revenues when persuasive evidence of an arrangement exists, delivery has occurred or services have been rendered, the fee is fixed or determinable, and there is reasonable assurance that the related amounts are collectible in accordance with ASC 605, Revenue Recognition.

(o) Research and development expenses

Elements of research and development expenses primarily include (1) payroll and other related costs of personnel engaged in research and development activities, (2) in-licensed patent rights fee of exclusive development rights of drugs granted to the Group, (3) costs related to preclinical testing of the Group’s technologies under development and clinical trials such as payments to contract research organizations (“CROs”), investigators and clinical trial sites that conduct our clinical studies (4) costs to develop the product candidates, including raw materials and supplies, product testing, depreciation, and facility related expenses, (5) other research and development expenses. Research and development expenses are charged to expense as incurred when these expenditures relate to the Group’s research and development services and have no alternative future uses. The conditions enabling capitalization of development costs as an asset have not yet been met and, therefore, all development expenditures are recognized in profit or loss when incurred.

(p) Deferred income

Deferred income consists of deferred income from government grants and American Depositary Receipts (the "ADR") Program Agreement with ADR depositary bank (the “DB”) in July 2017.

Government grants consist of cash subsidies received by the Group's subsidiaries in the PRC from local governments. Grants received as incentives for conducting business in certain local districts with no performance obligation or other restriction as to the use are recognized when cash is received. Cash grants of $298,072, $2,065,510 and $855,158 were included in other income for the years ended December 31, 2015, 2016 and 2017, respectively. Grants received with government specified performance obligations are recognized when all the obligations have been fulfilled. If such obligations are not satisfied, the Company may be required to refund the subsidy. Cash grants of $778,434 and $912,124 were recorded in deferred income as of December 31, 2016 and 2017 respectively, which will be recognized when the government specified performance obligation is satisfied.

According to the ADR arrangements, the Group will have the right to receive reimbursements after the closing of IPO as a return for using DB's services. All the reimbursements are subject to the compliance of the Group on all terms of the contract, including the non-existence of default conditions stipulated in the contracts. The Group performed detailed assessments over such conditions and deemed the potential for these conditions to materialize to be remote as of December 31, 2017. The reimbursements are recognized over the five-year contract term as other income. $78,000 was recorded in other income for the year ended December 31, 2017, and $1,482,000 was recorded in deferred income as of December 31, 2017.

(q) Leases

Leases are classified at the inception date as either a capital lease or an operating lease. the Group assesses a lease to be a capital lease if any of the following conditions exist: (1) ownership is transferred to the lessee by the end of the lease term, (2) there is a bargain purchase option, (3) the lease term is at least 75% of the property's estimated remaining economic life or (4) the present value of the minimum lease payments at the beginning of the lease term is 90% or more of the fair value of the leased property to the lessor at the inception date. A capital lease is accounted for as if there was an acquisition of an asset and an incurrence of an obligation at the inception of the lease. The Group has no capital leases for the years presented.

All other leases are accounted for as operating leases wherein rental payments are expensed on a straight-line basis over the periods of their respective lease terms. The Group leases office space and employee accommodation under operating lease agreements. Certain of the lease agreements contain rent holidays. Rent holidays are considered in determining the straight-line rent expense to be recorded over the lease term. The lease term begins on the date of initial possession of the lease property for purposes of recognizing lease expense on straight-line basis over the term of the lease.

(r) Comprehensive loss

Comprehensive loss is defined as the changes in equity of the Group during a period from transactions and other events and circumstances excluding transactions resulting from investments by owners and distributions to owners. Among other disclosures, ASC 220, Comprehensive Income, requires that all items that are required to be recognized under current accounting standards as components of comprehensive loss be reported in a financial statement that is displayed with the same prominence as other financial statements. For each of the periods presented, the Group's comprehensive loss includes net loss and foreign currency translation adjustments, which are presented in the consolidated statements of comprehensive loss.

(s) Stock-based compensation

Awards granted to employees

The Group grants share options to eligible employees, management and directors and accounts for these share based awards in accordance with ASC 718, Compensation-Stock Compensation.

Employees' share-based awards are measured at the grant date fair value of the awards and recognized as expenses (1) immediately at grant date if no vesting conditions are required; or (2) using graded vesting method over the requisite service period, which is the vesting period.

All transactions in which goods or services are received in exchange for equity instruments are accounted for based on the fair value of the consideration received or the fair value of the equity instrument issued, whichever is more reliably measurable.

To the extent the required vesting conditions are not met resulting in the forfeiture of the share-based awards, previously recognized compensation expense relating to those awards are reversed.

The Group, with the assistance of an independent third-party valuation firm, determined the fair value of the stock options granted to employees. The binomial option pricing model was applied in determining the estimated fair value of the options granted to employees.

Awards granted to non-employees

The Group has accounted for equity instruments issued to non-employees in accordance with the provisions of ASC 505, Equity-Based Payments to Non-Employees. All transactions in which goods or services are received in exchange for equity instruments are accounted for based on the fair value of the consideration received or the fair value of the equity instrument issued, whichever is more reliably measurable. The measurement date of the fair value of the equity instrument issued is the date on which the counterparty's performance is completed as there is no associated performance commitment. The expense is recognized in the same manner as if the Group had paid cash for the services provided by the non-employees in accordance with ASC 505.

(t) Income taxes

The Group uses the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized.

The Group evaluates its uncertain tax positions using the provisions of ASC 740, Income Taxes, which requires that realization of an uncertain income tax position be recognized in the financial statements. The benefit to be recorded in the financial statements is the amount most likely to be realized assuming a review by tax authorities having all relevant information and applying current conventions. It is the Group's policy to recognize interest and penalties related to unrecognized tax benefits, if any, as a component of income tax expense. No unrecognized tax benefits and related interest and penalties were recorded in any of the periods presented.

(u) Earnings (loss) per share

Basic earnings (loss) per ordinary share is computed by dividing net income (loss) attributable to ordinary shareholders by weighted average number of ordinary shares outstanding during the period.

The Group's convertible preferred shares are participating securities as the preferred shares participate in undistributed earnings on an as-if-converted basis. Accordingly, the Group uses the two-class method whereby undistributed net income is allocated on a pro rata basis to each participating share to the extent that each class may share income for the period. Undistributed net loss is not allocated to preferred shares because they are not contractually obligated to participate in the loss allocated to the ordinary shares.

Diluted earnings (loss) per ordinary share reflects the potential dilution that could occur if securities were exercised or converted into ordinary shares. The Group had convertible preferred shares, warrants, stock options and non-vested restricted shares, which could potentially dilute basic earnings (loss) per share in the future. To calculate the number of shares for diluted earnings (loss) per share, the effect of the convertible redeemable preferred shares and warrants is computed using the as-if-converted method; the effect of the stock options and non-vested restricted shares is computed using the treasury stock method. The computation of diluted earnings (loss) per share does not assume exercise or conversion of securities that would have an anti‑dilutive effect.

(v) Segment information

In accordance with ASC 280, Segment Reporting, the Group's chief operating decision maker, the Chief Executive Officer, reviews the consolidated results when making decisions about allocating resources and assessing performance of the Group as a whole and hence, the Group has only one reportable segment. The Group does not distinguish between markets or segments for the purpose of internal reporting. As the Group's long-lived assets are substantially located in and derived from the PRC, no geographical segments are presented.

(w) Concentration of risks

Concentration of suppliers

The following suppliers accounted for 10% or more of research and development expenses for the years ended December 31, 2015, 2016 and 2017:

	Year ended December 31,
	2015		2016		2017
	$		$		$
A		5,703,000	*		*
B	*			14,625,500	*
C	*		*			7,651,617
D	*		*			7,104,015

*	Represents less than 10% of research and development expenses for the years ended December 31, 2015, 2016 and 2017.

Concentration of credit risk

Financial instruments that are potentially subject to significant concentration of credit risk consist of cash and cash equivalents and prepayments for equipment. The carrying amounts of cash and cash equivalents represent the maximum amount of loss due to credit risk. As of December 31, 2016 and 2017, all of the Group’s cash and cash equivalents were held by major financial institutions located in the PRC and international financial institutions outside of the PRC which management believes are of high credit quality and continually monitors the credit worthiness of these financial institutions. With respect to the prepayment to suppliers, the Company performs on-going credit evaluations of the financial condition of these suppliers.

Foreign currency risk

Renminbi (“RMB”) is not a freely convertible currency. The State Administration of Foreign Exchange, under the authority of the People's Bank of China, controls the conversion of RMB into foreign currencies. The value of RMB is subject to changes in central government policies and to international economic and political developments affecting supply and demand in the China Foreign Exchange Trading System market. The cash and cash equivalents of the Group included aggregated amounts of RMB44,156,161 and RMB25,660,869, which were denominated in RMB, as of December 31, 2016 and 2017, respectively, representing 8% and 2% of the cash and cash equivalents as of December 31, 2016 and 2017, respectively.

(x) Share consolidation (“reverse stock split”)

On August 30, 2017, the Company effected a six-to-one share consolidation of all the ordinary shares and preferred shares. All number of shares, par value and per share amounts for all periods presented in these consolidated financial statements and accompanying notes have been adjusted retrospectively, where applicable, to reflect this share consolidation.

(y) Recent accounting pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Updates (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606), to clarify the principles of recognizing revenue and create common revenue recognition guidance between U.S. GAAP and International Financial Reporting Standards (“IFRS”). An entity has the option to apply the provisions of ASU 2014-09 either retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of initially applying this standard recognized at the date of initial application. ASU 2014-09 is effective for fiscal years and interim periods within those years beginning after December 15, 2016, and early adoption is not permitted. In August 2015, the FASB updated this standard to ASU 2015-14, the amendments in this Update defer the effective date of Update 2014-09 so that the Update should be applied to annual reporting periods beginning after December 15, 2017 and earlier application is permitted only as of annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting period.

In May 2016, FASB issued ASU 2016-12 Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients. The amendments in this Update do not change the core principle of the guidance in Topic 606. Rather, the amendments in this Update affect only the narrow aspects of Topic 606. The areas improved include: (1) Assessing the Collectability Criterion in Paragraph 606-10-25-1(e) and Accounting for Contracts That Do Not Meet the Criteria for Step 1; (2) Presentation of Sales Taxes and Other Similar Taxes Collected from Customers; (3) Noncash Consideration; (4) Contract Modifications at Transition; (5) Completed Contracts at Transition; and (6) Technical Correction. The effective date and transition requirements for the amendments in this Update are the same as the effective date and transition requirements for Topic 606 (and any other Topic amended by Update 2014-09).

The Group is in a development stage, with no revenues to date.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize most leases on the balance sheet. This ASU requires lessees to recognize a right-of-use asset and lease liability for all leases with terms of more than 12 months. Lessees are permitted to make an accounting policy election to not recognize the asset and liability for leases with a term of twelve months or less. The ASU does not significantly change the lessees' recognition, measurement and presentation of expenses and cash flows from the previous accounting standard. Lessors' accounting under the ASC is largely unchanged from the previous accounting standard. In addition, the ASU expands the disclosure requirements of lease arrangements. Lessees and lessors will use a modified retrospective transition approach, which includes a number of practical expedients. The provisions of this guidance are effective for annual periods beginning after December 15, 2018, and interim periods within those years, with early adoption permitted. The Group is currently evaluating this ASU to determine the full impact on its consolidated financial statements, as well as the impact of adoption on policies, practices and systems. As of December 31, 2017, the Group has $3.0 million of future minimum operating lease commitments that are not currently recognized on its consolidated balance sheets (see Note 16). Therefore, the Group would expect changes to its consolidated balance sheets for the recognition of these and any additional leases entered into in the future upon adoption.

In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting. The guidance provides clarity and reduces diversity in practice and cost and complexity when accounting for a change to the terms or conditions of a share-based payment award. The amendments in this update are effective for all entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted. The Group does not expect the requirements of ASU 2017-09 will have a material impact on the consolidated financial statements.

Cash and Cash Equivalents

12 Months Ended

Dec. 31, 2017

Cash And Cash Equivalents [Abstract]

Cash and Cash Equivalents

3.	Cash and cash equivalents

	As of December 31,
	2016		2017
	$		$
Cash at bank and in hand		36,531,272		204,008,828
Cash equivalents		47,417,498		25,651,320
		83,948,770		229,660,148
Denominated in:
US$		77,463,141		224,878,393
RMB (note (i))		6,365,311		3,927,163
Australia dollar ("A$")		120,318		854,592
		83,948,770		229,660,148

Note:

(i)	Certain cash and bank balances denominated in RMB were deposited with banks in the PRC. The conversion of these RMB denominated balances into foreign currencies is subject to the rules and regulations of foreign exchange control promulgated by the PRC government.

Investment in Equity Investees

12 Months Ended

Dec. 31, 2017

Equity And Cost Method Investment [Abstract]

Investment in equity investees

4.	Investment in equity investees

In June 2017, the Group entered into an agreement with three third-parties to launch JING Medicine Technology (Shanghai) Ltd. (“JING”), an entity which will provide services for drug discovery and development, consultation and transfer of pharmaceutical technology. The capital contribution by the Group will be RMB26.3 million ($3.9 million) in cash, representing 20% of the equity interest of JING. On July 5, 2017, RMB13.1 million ($1.9 million) was paid by the Group, and the remainder will be paid upon capital calls received from JING by the end of 2027. The Group accounts for this investment using the equity method of accounting because the Group does not control the investee but has the ability to exercise significant influence over the operating and financial policies of the investee. The Group recorded its share of loss in this investee of $249,652 for the year ended December 31, 2017.

In October 2016, the Group invested $500,000 in a private company over which the Group does not have significant influence or control and accounted for the investment using cost method of accounting. In April 2017, the Group disposed its investment to Quan Venture Fund I, L.P. for cash consideration of approximately $500,000 and no gain/loss was recognized upon disposal (Note 10).

Property and Equipment

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property and Equipment

5.	Property and equipment

Property and equipment consist of the following:

	As of December 31,
	2016			2017
	$			$
Office equipment		49,432			273,339
Electronic equipment		66,271			160,772
Vehicle		76,636			81,360
Laboratory equipment		593,582			1,686,133
Manufacturing equipment		—			2,832,726
Leasehold improvements		465,428			3,227,150
Construction in progress		252,509			4,252,894
		1,503,858			12,514,374
Less: accumulated depreciation		(257,800	)		(660,610	)
Property and equipment, net		1,246,058			11,853,764

Depreciation expenses for the years ended December 31, 2015, 2016 and 2017 were $125,774, $198,224 and $545,705, respectively.

Income Tax

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income tax

6.	Income Tax

Cayman Islands

Zai Lab Limited and ZLIP Holding Limited are incorporated in the Cayman Islands. Under the current laws of the Cayman Islands, Zai Lab Limited and ZLIP Holding Limited are not subject to tax on income or capital gain. Additionally, the Cayman Islands does not impose a withholding tax on payments of dividends to shareholders.

British Virgin Islands Taxation

ZL Capital Limited is incorporated in the British Virgin Islands. Under the current laws of the British Virgin Islands, ZL Capital Limited is not subject to income tax.

Australia

Zai Lab (AUST) Pty., Ltd. is incorporated in Australia and is subject to corporate income tax at a rate of 30%. Zai Lab (AUST) Pty., Ltd. has no taxable income for all periods presented, therefore, no provision for income taxes is required.

Hong Kong

Zai Lab (Hong Kong) Limited is incorporated in Hong Kong. Companies registered in Hong Kong are subject to Hong Kong profits tax on the taxable income as reported in their respective statutory financial statements adjusted in accordance with relevant Hong Kong tax laws. The applicable tax rate is 16.5% in Hong Kong. For the years ended December 31, 2015, 2016 and 2017, Zai Lab (Hong Kong) Limited did not make any provisions for Hong Kong profit tax as there were no assessable profits derived from or earned in Hong Kong for any of the periods presented. Under the Hong Kong tax law, Zai Lab (Hong Kong) Limited is exempted from income tax on its foreign-derived income and there are no withholding taxes in Hong Kong on remittance of dividends.

PRC

Zai Lab (Shanghai) Co., Ltd., Zai Lab (Suzhou) Co., Ltd., and Zai Biopharmaceutical (Suzhou) Co., Ltd. are subject to the statutory rate of 25% in accordance with the Enterprise Income Tax law (the "EIT Law").

No provision for income taxes has been required to accrue because the Company and all of its owned subsidiaries are in cumulative loss positions for all the periods presented.

Loss before income taxes consists of:

	Year ended December 31,
	2015		2016		2017
	$		$		$
Cayman		2,036,806		2,454,660		3,886,673
BVI		—		—		8,375
PRC		4,938,688		26,111,094		40,971,742
HK		9,869,007		8,010,908		6,240,462
AUST		1,177,236		935,550		(723,076	)
		18,021,737		37,512,212		50,384,176

Reconciliations of the differences between the PRC statutory income tax rate and the Group’s effective income tax rate for the years ended December 31, 2015, 2016 and 2017 are as follows:

	Year ended December 31,
	2015			2016			2017
	$			$			$
Statutory income tax rate		25	%		25	%		25	%
Share-based compensations		(3.68	%)		(2.92	%)		(3.27	%)
Non-deductible expenses		(7.19	%)		(1.59	%)		(0.79	%)
Effect of different tax rate of subsidiary operation in other jurisdictions		(7.15	%)		(3.33	%)		(3.06	%)
Changes in valuation allowance		(6.98	%)		(17.16	%)		(17.88	%)
Effective income tax rate		—			—			—

The principal components of the deferred tax assets and liabilities are as follows:

	Year ended December 31,
	2015			2016			2017
	$			$			$
Deferred tax assets:
Depreciation of property and equipment, net		2,415			3,892			5,964
Accrued expenses		72,408			—			—
Government grants		16,025			166,336			187,762
Net operating loss forwards		1,729,009			8,086,361			17,075,387
Less: valuation allowance		(1,819,857	)		(8,256,589	)		(17,269,113	)
Deferred tax assets, net		—			—			—

The Group considers positive and negative evidence to determine whether some portion or all of the deferred tax assets will be more likely than not realized. This assessment considers, among other matters, the nature, frequency and severity of recent losses and forecasts of future profitability. These assumptions require significant judgment and the forecasts of future taxable income are consistent with the plans and estimates the Group is using to manage the underlying businesses. Valuation allowances are established for deferred tax assets based on a more likely than not threshold. The Group’s ability to realize deferred tax assets depends on its ability to generate sufficient taxable income within the carry forward periods provided for in the tax law. In 2016 and 2017, the Group has determined that the deferred tax assets on temporary differences and net operating loss carry forwards are related to certain subsidiaries, for which the Group is not able to conclude that the future realization of those net operating loss carry forwards and other deferred tax assets are more likely than not. As such, it has fully provided valuation allowance for the deferred tax assets as of December 31, 2016 and 2017. Amounts of operating loss carry forwards were $7,969,098, $34,716,071 and $72,137,289 for the year ended December 31, 2015, 2016 and 2017, respectively, which are expected to expire from 2019 to 2022.

Movement of the valuation allowance is as follows:

	2016			2017
	$			$
Balance as of January 1,		(1,819,857	)		(8,256,589	)
Additions		(6,436,732	)		(9,012,524	)
Balance as of December 31,		(8,256,589	)		(17,269,113	)

Uncertainties exist with respect to how the current income tax law in the PRC applies to the Group’s overall operations, and more specifically, with regard to tax residency status. The EIT Law includes a provision specifying that legal entities organized outside of the PRC will be considered residents for Chinese income tax purposes if the place of effective management or control is within the PRC. The implementation rules to the EIT Law provide that non-resident legal entities will be considered PRC residents if substantial and overall management and control over the manufacturing and business operations, personnel, accounting and properties, occurs within the PRC. Despite the present uncertainties resulting from the limited PRC tax guidance on the issue, the Group does not believe that the legal entities organized outside of the PRC within the Group should be treated as residents for EIT Law purposes. If the PRC tax authorities subsequently determine that the Company and its subsidiaries registered outside the PRC should be deemed resident enterprises, the Company and its subsidiaries registered outside the PRC will be subject to the PRC income taxes, at a rate of 25%. The Group is not subject to any other uncertain tax position.

Other Payables

12 Months Ended

Dec. 31, 2017

Other Liabilities Current [Abstract]

Other Payables

7.	Other payables

	As of December 31,
	2016		2017
	$		$
Payroll		573,802		1,607,740
Professional service fee		23,721		714,764
Payables for purchase of property and equipment		—		413,657
Other taxes payable		—		17,793
Others		152,595		347,505
		750,118		3,101,459

Convertible Preferred Shares and Warrants

12 Months Ended

Dec. 31, 2017

Temporary Equity Disclosure [Abstract]

Convertible preferred shares and warrants

8.	Convertible preferred shares and warrants

Upon the completion of the Company's IPO on September 20, 2017, all of the outstanding Series A1, A2, B1, B2 and C convertible preferred shares were converted into 28,905,083 ordinary shares. The history of the issuance of the preferred shares is as following:

In August 2014 and April 2015, the Company issued 6,244,443 Series A1 convertible preferred shares (“Series A1 Preferred Shares”) and 8,442,221 Series A2 convertible preferred shares (“Series A2 Preferred Shares”) with a par value $0.00006 per share to a group of investors for a cash consideration of $8,028,572 or $1.2857 per share and $18,278,572 or $2.1651 per share, respectively. In August 2014, $2,000,000 in convertible loans issued in March and April of 2014 to certain investors who purchased Series A1 Preferred Shares were converted into 2,222,222 Series A1 Preferred Shares in connection with the offering at a per share price of $0.90.

On December 31, 2015, as an inducement to participate in the contemplated issuance of Series B1 Preferred Shares and Series B2 Preferred Shares, the Company entered into an agreement with one investor to issue warrants to purchase up to 461,808 Series A2 Preferred Shares at $2.1651 per share, as adjusted from time to time pursuant to the agreement. The fair value of the warrants of $1,980,000 was expensed on the date of issuance (as opposed to being treated as a cost of equity issuance because the warrants would have become exercisable after the passage of time in the absence of an equity offering).

In January and April 2016, the Company issued 5,562,335 Series B1 convertible preferred shares (“Series B1 Preferred Shares”) and 3,973,096 Series B2 convertible preferred shares (“Series B2 Preferred Shares”) with a par value of $0.00006 per share to a group of investors including existing preferred share investors for a cash consideration of $53,100,000 or $9.5464 per share and $53,100,000 or $13.3649 per share, respectively.

In June 2017, the Company issued 1,998,958 Series C convertible redeemable preferred shares (“Series C Preferred Shares”) with a par value of $ 0.00006 per share to a group of investors including existing preferred share investors for a cash consideration of $30,000,000 or $15.0078 per share.

On July 19, 2017, the investor holding the warrants exercised the warrants to purchase 461,808 Series A2 Preferred Shares at $2.1651 per share.

The key terms of the Series A1, A2, B1, B2 and C Preferred Shares are as follows:

Conversion rights

Each holder of Series A1, A2, B1 and B2 Preferred Shares shall have the right, at such holder’s sole discretion, to convert all or any portion of the Series A1, A2, B1 and B2 Preferred Shares into ordinary shares based on a one-for-one basis at any time. The initial conversion price is the issuance price of Series A1, A2, B1 and B2 Preferred Shares.

Each holder of Series C Preferred Shares shall have the right, at such holders’ sole discretion, to convert all or any portion of the Series C Preferred Shares into ordinary shares based at any time. The initial conversion price shall equal the lower of (1) the issuance price of Series C Preferred Shares and (2) Calculated Price which is one hundred percent minus the discount rate of fifteen percent (the “Discount Rate”) multiplied by the offering price of the ordinary shares of the Company to the public on the date of the Qualified Initial Public Offering (“QIPO”). The Discount Rate will increase at increments of an additional two percent as of the first day of each successive six months period after June 2018 but shall in no event exceed twenty percent.

The conversion price of Series A1, A2, B1, B2 and C Preferred Shares is subject to adjustment in the event of (1) stock splits, share combinations, share dividends and distribution, recapitalizations and similar events, and (2) issuance of new securities at a price per share less than the conversion price in effect on the date of or immediately prior to such issuance. In that case, the conversion price shall be reduced concurrently to the subscription price of such issuance.

The Series A1, A2, B1, B2 and C Preferred Shares will be automatically converted into ordinary shares at the then applicable conversion price upon the earlier of (1) the closing of a QIPO, or (2) the date specified by written consent or agreement of majority holders of Series A1, A2, B1, B2 and C Preferred Shares.

Voting rights

The Series A1, A2, B1, B2 and C Preferred Shares are entitled to vote with ordinary shareholders on an as-converted basis. The holders of the Preferred Shares also have certain veto rights including, but not limited to, an increase or decrease in the total number of directors and change of board composition, appointment or removal of senior management, approval of business plan and operating budget, dividend declaration, any merger, split, reorganization or consolidation.

Dividends

The holders of Series A1, A2, B1, B2 and C Preferred Share may be entitled to receive dividends accruing at the rate of 8% per annum of the issuance price of Preferred Shares (the “Dividend Rate”). For holders of Series C Preferred Shares, the Dividend Rate shall increase by an additional one percent per annum for each successive six months period after June 2018 but shall in no event exceed ten percent.

In addition, holders of Series A1, A2, B1, B2 and C Preferred Shares are also entitled to dividends on the Company's ordinary shares on an as if converted basis and must be paid prior to any payment on ordinary shares. All dividends shall be payable only when, as, and if declared by the Board of Directors and shall be noncumulative.

Liquidation preference

In the event of any liquidation, dissolution or winding up of the Company, either voluntary or involuntary, the holders of Series A1 and A2 Preferred Shares are entitled to receive, prior to any distribution to the holders of ordinary shares, an amount per share equal to the Series A original issue price, plus accrued but unpaid dividends (the "Series A Preference Amount").

In the event of any liquidation, dissolution or winding up of the Company, either voluntary or involuntary, the holders of Series B1 and B2 Preferred Shares are entitled to receive, prior to any distribution to the holders of ordinary shares, an amount per share equal the Series B original issue price plus five percent (5%) simple interest on such Series B issue price accrued annually from the applicable Series B issue date, plus accrued but unpaid dividends (the "Series B Preference Amount").

In the event of any liquidation, dissolution or winding up of the Company, either voluntary or involuntary, the holders of Series C Preferred Shares are entitled to receive, prior to any distribution to the holders of any other class or series of equity securities, an amount per share equal the issuance price of Series C Preferred Shares plus non-compounding simple interest accruing at five percent (5%) per annum on the issuance price and plus any accrued but unpaid dividends (the "Series C Preference Amount").

In the event insufficient funds are available to pay in full the Preference Amount in respect of each preferred shareholders, the sequence of liquidation right of all series of preferred shares was as follows:

(1) Series C Preferred Shares;

(2) Series B1 and B2 Preferred Shares;

(3) Series A1 and A2 Preferred Shares.

After the Preference Amount has been paid, any remaining funds or assets legally available for distribution shall be distributed pro rata among the preferred shareholders together with ordinary shares.

A liquidation event includes, (1) any liquidation, dissolution or winding up of the Company, whether voluntary or involuntary; the exclusive licensing of all or substantially all of the Group Companies’ intellectual property, taken as a whole, to a third party; (2) any sale of all or substantially all of the assets of the Group to a third party unaffiliated with any member of the Group; or (3) the transfer (whether by merger, reorganization or other transaction) in which a majority of the outstanding voting power of the Company is transferred (excluding any sale of shares by the Company for capital raising purposes).

Redemption

In the event that a QIPO has not been completed by June 2022, holders of the Series C Preferred Shares may at any time thereafter require that the Company redeem all of the Series C Preferred Shares held by such holder at a redemption price per share equal to the sum of (1) an amount equal to the original issuance price, and (2) an additional amount which would result in holders of Series C Preferred Shares receiving an internal rate of return of fifteen percent after taking into consideration the payment of issuance price of Series C Preferred Shares and all prior distributions received.

The key terms of the warrants are as follows:

Vesting date

The warrants were vested on April 1, 2016.

Exercise period

If not previously exercised, the warrants shall expire on the earlier of (1) the sixth (6th) anniversary of the issue date or (2) ninety (90) days prior to the date on which the Company consummates a QIPO.

The Company has classified the Series A1, A2, B1, B2 and C Preferred Shares as mezzanine equity as these convertible preferred shares are redeemable upon the occurrence of a conditional event outside of the Company’s control (i.e. a liquidation event or failure to complete the QIPO within required period). The holders of the Series A1, A2, B1, B2 and C Preferred Shares have a liquidation preference and will not receive the same form of consideration upon the occurrence of the conditional event as the ordinary shareholders would. The holders of the Series A1, A2, B1, B2 and C Preferred Shares have the ability to convert the instrument into the Company's ordinary shares. The conversion option of the convertible preferred shares did not qualify for bifurcation accounting because the conversion option was clearly and closely related to the host instrument and the underlying ordinary shares are not publicly traded nor readily convertible into cash.

The Company has determined that there was no beneficial conversion feature ("BCF") attributable to the Series A1, A2, B1, B2 and C Preferred Shares, as the effective conversion price was greater than the fair value of the ordinary shares on the respective commitment date.

The Company concluded that redemption of that the Series A1, A2, B1, B2 and C Preferred Shares was not probable due to the remote likelihood of a liquidation event and the expected successful QIPO within five years. Therefore, no adjustment was made to the initial carrying amount of the Series A1, A2, B1, B2 and C Preferred Shares.

The warrants are freestanding instruments and are recorded as liabilities in accordance with ASC480. The Series A1, A2, B1, B2 and C Preferred Shares were initially recorded as mezzanine equity equal to the proceeds received. The warrants are initially recognized at fair value, with subsequent changes in fair value recorded in gain or loss. For the year ended December 31, 2015 and 2016, the Company recognized a loss from the increase in fair value of the warrants of $2.0 and $1.9 million respectively. For the year ended December 31, 2017, the Company recognized a gain from the decrease in fair value of the warrants of $0.2 million.

Loss Per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Loss per share

9.	Loss per share

Basic and diluted net loss per share for each of the years presented are calculated as follow:

	For the year ended December 31,
	2015			2016			2017
Numerator:
Net loss attributable to ordinary shareholders		(18,021,737	)		(37,512,212	)		(50,384,176	)
Denominator:
Weighted average number of ordinary shares- basic and diluted		8,693,655			9,439,028			21,752,757
Net loss per share-basic and diluted		(2.07	)		(3.97	)		(2.32	)

The Group has determined that its convertible preferred shares are participating securities as the preferred shares participate in undistributed earnings on an as-if-converted basis. The holders of the preferred shares are entitled to receive dividends on a pro rata basis, as if their shares had been converted into ordinary shares. Accordingly, the Group used the two-class method of computing earnings per share, for ordinary and preferred shares according to participation rights in undistributed earnings, However, undistributed net loss is only allocated to ordinary shareholders because holders of preferred shares were not contractually obligated to share losses.

As a result of the Group’s net loss for the three years ended December 31, 2015, 2016 and 2017, preferred shares, share options, non-vested restricted shares and warrants outstanding in the respective periods were excluded from the calculation of diluted loss per share as their inclusion would have been anti-dilutive.

	As of December 31,
	2015		2016		2017
Number of Series A1 Shares outstanding		8,466,665		8,466,665		—
Number of Series A2 Shares outstanding		8,442,221		8,442,221		—
Number of Series B1 Shares outstanding		—		5,562,335		—
Number of Series B2 Shares outstanding		—		3,973,096		—
Share options		4,309,232		7,228,141		6,548,377
Non-vested restricted shares		2,948,148		2,309,490		693,333
Warrants		461,808		461,808		—

Related Party Transactions

12 Months Ended

Dec. 31, 2017

Related Party Transactions

10.	Related party transactions

The table below sets forth the major related party and the relationship with the Group as of December 31, 2017:

Company Name		Relationship with the Group
Quan Venture Fund I, L.P.		Significantly influenced by Samantha Du, founder, chairman and CEO of the Company

Qiagen (Suzhou) Translational Medicine Co., Ltd.		Significant influence held by Samantha Du’s immediate family

The Group paid expenditures to its related party:

Research and development expenditures	Year ended December 31,
	2015		2016		2017
	$		$		$
Qiagen (Suzhou) Translational Medicine Co. Ltd.		96,656		—		—

On April 30, 2017, the Group disposed its investment in a cost method investee to Quan Venture Fund I, L.P. for a cash consideration of $500,000 and no gain/loss was recognized upon disposal.

Share-based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-based compensation

11.	Share-based compensation

Share options

On March 5, 2015, the Board of Directors of the Company approved an Equity Incentive Plan (the “2015 Plan”) which is administered by the Board of Directors. Under the 2015 Plan, the Board of Directors may grant options to purchase ordinary shares to management including officers, directors, employees and individual advisors who render services to the Group to purchase an aggregate of no more than 4,140,945 ordinary shares of the Group (“Option Pool”). On October 22, 2015, March 9, 2016 and August 25, 2016, the Board of Directors approved the increase in the Option Pool to 7,369,767 ordinary shares. These options granted have a contractual term of 10 years and generally vest over a five year period, with 20% of the awards vesting one year after the grant date and the remainder of the awards vesting on a monthly basis thereafter.

In March and October 2015, the Group granted 870,449 and 3,438,783 share options to certain of the Group’s management and employees at an exercise price of $0.6 per share, respectively. These options granted have a contractual term of 10 years and generally vest over a five year period, with 20% of the awards vesting one year after the grant date and the remainder of the awards vesting on a monthly basis thereafter.

In March 2016, the Group granted 1,157,793 share options to certain of the Group’s management and employees at an exercise price of $1.2 per share. These options granted have a contractual term of 10 years and generally vest over a five year period, with 20% of the awards vesting anniversary year after the grant date.

In August 2016, the Group granted 1,760,368 share options to certain of the Group’s management and employees at an exercise price of $1.74 per share, respectively. These options granted have a contractual term of 10 years and generally vest over a five year period, with 20% of the awards vesting on the anniversary of the grant date each year.

In August and December 2016, the Group granted 416 and 416 share options to certain individual advisors of the Group at an exercise price of $1.74 per share. These options granted have a contractual term of 10 years and generally vest over a three year period, with 33.33% of the awards vesting anniversary year after the grant date.

In May 2017, the Group granted 158,313 share options to certain management and employees of the Group at an exercise price of $3.0 per share under the 2015 Plan. These options granted have a contractual term of 10 years and generally vest over a four or five year period, with 25% or 20% of the awards vesting on each annual anniversary after the grant date.

In May 2017, the Group granted 4,583 share options to certain individual advisors of the Group at an exercise price of $3.0 per share. These options granted have a contractual term of 10 years and generally vest over a three year period, with 33.33% of the awards vesting anniversary year after the grant date.

In connection with the completion of the IPO, the Board of Directors has approved the 2017 Equity Incentive Plan (the “2017 Plan”) and all equity-based awards will be granted under the 2017 Plan subsequent to the IPO.

In September 2017, the Group granted 101,584 share options to certain management and employees of the Group at an exercise price of $18.0 per share under the 2017 Plan. These options granted have a contractual term of 10 years and generally vest over a five year period, with 20% of the awards vesting anniversary year after the grant date.

The binomial option-pricing model was applied in determining the estimated fair value of the options granted. The model requires the input of highly subjective assumptions including the estimated expected stock price volatility and, the exercise multiple for which employees are likely to exercise share options. For expected volatilities, the Group has made reference to the historical price volatilities of ordinary shares of several comparable companies in the same industry as the Group. For the exercise multiple, prior to the IPO, the Group had no historical exercise patterns as reference, thus the exercise multiple is based on management's estimation, which the Group believes is representative of the future exercise pattern of the options. The risk-free rate for periods within the contractual life of the option is based on the US treasury bonds with maturity similar to the maturity of the options as of valuation dates plus a China country risk premium. Prior to the completion of the Company’s IPO, the estimated fair value of the ordinary shares, at the option grant dates, was determined with assistance from an independent third-party valuation firm. The Group's management is ultimately responsible for the determination of the estimated fair value of its ordinary shares. With the completion of the Company’s IPO, a public trading market for the ADSs has been established, the Company uses the current share price as the fair value of underlying ordinary shares.

The following table presents the assumptions used to estimate the fair values of the share options granted in the years presented:

	March 2015			October 2015			March 2016			August 2016			December 2016			May 2017			September 2017
Risk-free rate of return		3.1	%		3.1	%		2.8	%		2.5	%		3.4	%		3.2	%		3.5	%
Contractual life of option	10 years			10 years			10 years			10 years			10 years			10 years			10 years
Estimated volatility rate		70	%		70	%		70	%		70	%		70	%		70	%		70	%
Expected dividend yield		0	%		0	%		0	%		0	%		0	%		0	%		0	%
Fair value of underlying ordinary shares		1.62			1.92			7.14			8.04			8.04			9.60			27.93

A summary of option activity under the Plan during the years ended December 31, 2015, 2016 and 2017 is presented below:

	Number of options			Weighted average exercise price		Weighted average remaining contractual term		Aggregate intrinsic value
				$		Years		$
Outstanding at January 1, 2015		—			—		—		—
Granted		4,309,232			0.60		—		—
Outstanding at December 31, 2015		4,309,232			0.60		9.68		18,874,438
Granted		2,918,993			1.53		—		—
Forfeited		(84	)		1.74		—		—
Outstanding at December 31, 2016		7,228,141			0.97		9.00		53,677,170
Granted		264,480			8.76		—		—
Exercised		(100,834	)		0.65		—		—
Forfeited		(843,410	)		1.11		—		—
Outstanding at December 31, 2017		6,548,377			1.28		8.06		130,668,851
Vested and Exercisable as of December 31, 2017		2,307,319			0.80		7.84		47,134,503
Vested or expected to vest as of December 31, 2017		6,548,377			1.28		8.06		130,668,851

The weighted-average grant-date fair value of the options granted in 2015, 2016 and 2017 were $1.62, $6.94 and $13.92 per share, respectively. The Group recorded compensation expense related to the options of $419,709, $3,524,733 and $4,751,933 for the year ended December 31, 2015, 2016 and 2017, respectively, which were classified in the accompanying consolidated statements of operations as follows:

	Year ended December 31,
	2015		2016		2017
	$		$		$
General and administrative		124,871		1,472,993		2,215,282
Research and development		294,838		2,051,740		2,536,651
Total		419,709		3,524,733		4,751,933

As of December 31, 2017, there was $18,419,319 of total unrecognized compensation expense related to unvested share options granted. That cost is expected to be recognized over a weighted-average period of 3.05 years.

Ordinary shares issued to Red Kingdom Investment Limited ("Red Kingdom")

Red Kingdom is a company incorporated in the British Virgin Islands in August 2013 and owned by a group of senior management including the Chief Executive Officer of the Company (the "CEO") of the Company and advisors of the Group and third-party investors. Red Kingdom has no activities and does not have employees. All the shareholders of the Red Kingdom have delegated their voting rights to the CEO of the Company.

On April 3, 2014, the Company issued 8,083,333 shares to Red Kingdom which are corresponding to the total outstanding shares of Red Kingdom for total consideration of $141,971. One share of Red Kingdom is entitled to indirectly all of the economic rights associated with the underlying ordinary shares of the Company. Of these shares, 7,847,500 shares were held by members of senior management and certain advisors of the Group, who paid par value.

In April and May 2014, Red Kingdom entered into restricted share arrangements with the members of senior management of the Group to secure their services, pursuant to which all of their 6,459,167 ordinary shares of the Red Kingdom became subject to transfer restrictions (the “Restricted Shares”). In addition, the Restricted Shares shall initially be unvested and subject to repurchase by Red Kingdom at par value upon voluntary or involuntary termination of employment by those senior management (the “Repurchase Right”). One fifth of the Restricted Shares shall vest and be released from the restrictions and Repurchase Right on each yearly anniversary from the date of the agreement. Accordingly, the Group measured the fair value of the non-vested Restricted Shares at grant date and recognizes the amount as compensation expense over the five year deemed service period using a graded vesting attribution model on a straight-line basis.

In April 2014, Red Kingdom entered into a restricted share arrangement with one of its advisors whereby all of their 350,000 ordinary shares of Red Kingdom became subject to transfer restrictions (the “Advisor Restricted Shares”). The Advisor Restricted Shares shall vest and be released from the Repurchase Right at the rate of twenty percent (20%) of the total number of Advisor Restricted Shares as each the contractually agreed milestones within each year (collectively, the “Milestones”) are determined to have been achieved by the Company. Accordingly, the Group measures the service expense based on the fair value of the Restricted Shares when the milestones are achieved.

The 1,038,333 shares the Company issued to Red Kingdom corresponded to the shares of Red Kingdom held by advisors of the Group, purchased for par value in 2014 are not subject to the transfer restrictions or other repurchase rights, and so were considered vested immediately at the date of grant and expensed.

On December 15, 2015, 1,921,000 unvested Restricted Shares granted to the CEO were deemed vested by the Company and the unrecognized share-based compensation of $1,152,600 as of the modification date was immediately recognized as compensation expense in the consolidated statements of operations.

On June 15, 2017, pursuant to the Board’s resolution, Red Kingdom distributed all of the ordinary shares that it held in the Group to all Red Kingdom shareholders, in accordance with the Articles of Association of Red Kingdom. All the prior restricted share arrangements in force as of the distribution date between Red Kingdom and members of senior management and advisors were amended to assign the rights and obligations of Red Kingdom thereunder to the Group (the “Transfer”). Before the Transfer, 811,667 restricted shares of Red Kingdom have been vested and 1,329,999 non-vested restricted shares of Red Kingdom have been repurchased by Red Kingdom due to the termination of employment by certain members of senior management and allocated to the founders of Red Kingdom at par value in 2017.

The following table summarized the non-vested restricted shares activities of Red Kingdom in 2017:

	Numbers of non-vested restricted shares			Weighted average grant date fair value
				$
Non-vested as of January 1, 2017		2,784,999			0.60
Vested		(811,667	)		0.60
Forfeited		(1,329,999	)		0.60
Transferred to the Company		(643,333	)		0.60
Non-vested as of December 31, 2017		—

Non-vested restricted shares

On April 3, 2014, the Company entered into a restricted share arrangement with Samantha Du, founder and Chairman and CEO to secure her services, pursuant to which all of her 3,500,000 ordinary shares of the Company became subject to transfer restrictions. In addition, the restricted shares shall initially be unvested and subject to repurchase by the Company at par value upon voluntary or involuntary termination of employment by the CEO (the “Repurchase Right”). One fifth of the restricted shares shall vest and be released from the restrictions and Repurchase Right on each yearly anniversary from the date of the agreement. The CEO retains the voting rights of such non-vested restricted shares and any additional securities or cash received as the result of ownership of such shares, such as a share dividend, become subject to restriction in the same manner. This arrangement has been accounted for as a performance-based plan. Accordingly, the Group measured the fair value of the non-vested restricted shares as of April 3, 2014 and is recognizing the amount as compensation expense over the five year deemed service period using a graded vesting attribution model for each separately vesting portion of the non-vested restricted shares.

On August 10, 2015, the Company entered into a restricted share arrangement with an individual advisor to secure their services, for 166,667 ordinary shares authorized for grant. In general, restrictions limit the sale or transfer of these shares during a three year period, and restrictions lapse proportionately over the three year period. During the three year period the Company upon voluntary or involuntary termination of service agreement by the individual advisor will repurchase unvested restricted shares at par (the “Repurchase Right”). On July 15, 2016 and August 25, 2016, 58,333 and 75,000 ordinary shares were authorized for grant to the individual advisor with the same Repurchase Right. The Repurchase Right terminates over the three years commencing August 10, 2015, July 15, 2016 and August 25, 2016 in 36 equal monthly instalments thereafter, or immediately prior to the consummation of an IPO of the Company. Any additional securities or cash received as the result of ownership of such shares, such as a share dividend, become subject to restriction in the same manner. For all restricted shares, the individual advisor has delegated his voting rights to the CEO of the Company. This arrangement has been accounted for as a reverse stock split followed by the grant of a restricted stock award under a performance-based plan. Accordingly, the Group measures the fair value at the date the services are completed which is monthly.

In March and May 2017, pursuant to the board resolution of the Company, the Repurchase Right to all the remaining 2,100,000 non-vested restricted shares of the CEO which were subject to the restricted share arrangement dated April 3, 2014 was removed and the unrecognized share-based compensation of $840,000 as of the modification date was immediately recognized as an expense in the consolidated statements of operations.

In Sep 2017, pursuant to the successful IPO of the Company, the Repurchase Right to all the remaining 134,516 non-vested restricted shares of the individual advisor which were subject to the restricted share arrangement dated August 10, 2015, July 15, 2016 and August 25, 2016 was terminated and the unrecognized share-based compensation of $2,421,288 as of the modification date was immediately recognized as an expense in the consolidated statements of operations.

On September 20, 2017, 50,000 ordinary shares were authorized for grant to the independent directors. One third of the restricted shares shall vest and be released from the restrictions on each yearly anniversary from the date of the agreement. Upon termination of the independent directors' service with the Group for any reason, any shares that are outstanding and not yet vested will be immediately be forfeited. This arrangement has been accounted for as a performance-based plan. Accordingly, the Group measured the fair value of the non-vested restricted shares as of September 20, 2017.

The following table summarized the Group’s non-vested restricted share activity in 2017:

	Numbers of non-vested restricted shares			Weighted average grant date fair value
				$
Non-vested as of January 1, 2017		2,309,490			1.31
Granted		50,000			27.93
Vested		(2,309,490	)		1.03
Transferred from Red Kingdom		643,333			0.60
Non-vested as of December 31, 2017		693,333			2.57

As of December 31, 2017, there was $1,517,160 of total unrecognized compensation expense related to non-vested Restricted Shares. The Group recorded compensation expense related to the restricted shares of $2,281,695, $1,400,545 and $5,179,173 for the year ended December 31, 2015, 2016 and 2017, respectively, which were classified in the accompanying consolidated statements of operations as follows:

	Year ended December 31,
	2015		2016		2017
	$		$		$
General and administrative		964,012		825,822		3,848,165
Research and development		1,317,683		574,723		1,331,008
Total		2,281,695		1,400,545		5,179,173

Accumulated Other Comprehensive Loss

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Accumulated Other Comprehensive Loss

12.	Accumulated other comprehensive loss

The movement of accumulated other comprehensive loss is as follows:

	Foreign currency translation adjustments
	$
Balance as of January 1, 2015		(4,727	)
Other comprehensive loss		(98,893	)
Balance as of December 31, 2015		(103,620	)
Other comprehensive loss		(594,912	)
Balance as of December 31, 2016		(698,532	)
Other comprehensive income		1,148,440
Balance as of December 31, 2017		449,908

Licenses and Collaborative Arrangement

12 Months Ended

Dec. 31, 2017

Research And Development [Abstract]

Licenses and collaborative arrangement

13.	Licenses and collaborative arrangement

License and collaboration agreement with Bristol-Myers Squibb Company (“BMS”)

In March 2015, the Group entered into a collaboration and license agreement with BMS, under which the Group obtained an exclusive license under certain patents and know-how of BMS to develop, manufacture, use, sell, import and commercialize brivanib, BMS’s proprietary multi-targeted kinase inhibitor, in mainland China, Hong Kong and Macau, or the licensed territory, in the licensed field of diagnosis, prevention, treatment or control of oncology indications, with the right to expand the licensed territory to include Taiwan and Korea under certain conditions. BMS retains the non-exclusive right to use the licensed compounds to conduct internal research and the exclusive right to use the licensed compounds to manufacture compounds that are not brivanib.

BMS has the option to elect to co-promote the licensed products in the licensed territory. If BMS exercises its co-promotion option, BMS will pay the Group an option exercise fee, and the Group will share with BMS the operating profits and losses of the licensed products in the licensed territory. If BMS does not exercise its co-promotion option, the Group will pay BMS milestone payments for the achievement of certain development and sales milestone events, and also tiered royalties at certain percentage rates on the net sales of the licensed products in the licensed territory, until the later of the expiration of the last-to-expire licensed patent covering the licensed product, the expiration of regulatory exclusivity for the licensed product, or the twelfth anniversary of the first commercial sale of the licensed product, in each case on a product-by-product and region-by-region basis.

The Group also has the right to opt-out of the commercialization of the licensed products in its licensed territory under certain conditions. If the Group elects to opt-out, BMS will have the right to commercialize the licensed products in the Group’s licensed territory and will pay the Group royalties on the net sales of the licensed products in its licensed territory. BMS has the option to use the data generated by the Group from the Group’s development of the licensed products to seek regulatory approval of the licensed products outside the Group’s licensed territory, and if BMS exercises such option, BMS will be obligated to make certain payments to the Group, including upfront, milestone and royalty payments.

The agreement may be terminated by either party for the other party’s uncured material breach, safety reasons or failure of the development of the licensed products. In addition, the Group has the right to terminate the agreement for convenience after a certain specified time period upon advance notice to BMS. BMS may also terminate the agreement for our bankruptcy or insolvency.

License and collaboration agreement with Sanofi

In July 2015, the Group entered into a license agreement with Sanofi, under which the Group obtained an exclusive and worldwide license under certain patents and know-how of Sanofi to develop, manufacture, use, sell, import and commercialize Sanofi’s ALK inhibitor, or the licensed compound (also known as ZL-2302), for any oncology indications in humans. Sanofi retains the non-exclusive right to use the licensed compound to conduct internal research.

Under the terms of the agreement, the Group made upfront payments to Sanofi totalling $0.5 million which were recorded as research and development expenses in 2015. If the Group successfully develops and commercializes the licensed product, the Group will make milestone payments to Sanofi for the achievement of certain development milestone events. In addition, the Group will pay to Sanofi tiered royalties at certain percentage rates of the net sales of the licensed products, until the later of the expiration of the last-to-expire licensed patent covering the licensed product, the expiration of regulatory exclusivity for the licensed product, or the tenth anniversary of the first commercial sale of the licensed product, in each case on a product-by-product and country-by-country basis. If the Group sublicenses, transfers or assigns (other than through a change of control transaction) the right to the licensed product to third parties, the Group is also required to pay to Sanofi a share of its sublicense income.

The Group at any time has the right to terminate this agreement for any reason or no reason at all by providing Sanofi with prior written notice.

License and collaboration agreement with UCB Biopharma Sprl (“UCB”)

In September 2015, the Group entered into a license agreement with UCB, under which the Group obtained an exclusive and worldwide license under certain patents and know-how of UCB to develop, manufacture, use, sell, import and commercialize UCB’s proprietary antibody UCB3000 or the licensed compound (also known as ZL-1101), for the treatment, prevention and diagnosis of any human diseases. UCB retains the non-exclusive right to use the licensed compound for its own research purposes.

Under the terms of the agreement, the Group made upfront payments to UCB totalling $0.8 million which was recorded as a research and development expense in 2016. If the Group successfully develops and commercializes the licensed products, the Group will make milestone payments to UCB for the achievement of certain development and sales milestone events. In addition, the Group will pay to UCB royalties at certain percentage rates on the net sales of the licensed products, until the later of the expiration of the last-to-expire licensed patent covering the licensed product, the expiration of regulatory exclusivity for the licensed product, or the tenth anniversary of the first commercial sale of the licensed product, in each case on a product-by-product and country-by-country basis. If the Group sublicenses the right to the licensed product to third parties, the Group is also required to pay to UCB a share of its sublicense income.

The Group has the right to terminate this agreement by providing UCB with prior written notice.

License and collaboration agreement with Hanmi Pharm, Co., Ltd. (“Hanmi”)

In November 2015, the Group entered into a collaboration and license agreement with Hanmi under which the Group obtained an exclusive right of license under certain patents and know-how of Hanmi to develop, manufacture, use, sell, import and commercialize Hanmi’s EGFR mutation specific TKI HM61713, or the licensed compound (also known as ZL-2303) for the treatment, diagnosis or prevention of any diseases or conditions in human. Hanmi retains the non-exclusive right to use the licensed compound for its own research purposes. Hanmi has the right of first negotiation to acquire the rights to the licensed products back from the Group upon successful completion of certain clinical development work.

Under the terms of the agreement, the Group made upfront payments amounted $6.0 million and $1.0 million to Hanmi in 2015 and 2016, respectively. If the Group successfully develop and commercialize the licensed products, the Group will make milestone payments to Hanmi for the achievement of certain development milestone events. In addition, the Group will pay to Hanmi royalties at certain percentage rates on the net sales of the licensed products in its licensed territory, until date of expiration of the latest of valid claim that claims the composition-of-matter of the licensed product, the expiration date of any regulatory data exclusivity for the licensed product, or the tenth anniversary of the first commercial sale of the licensed product.

The Group has the right to terminate this agreement by providing Hanmi with prior written notice.

License and collaboration agreement with Tesaro Inc., (“Tesaro”)

In September 2016, the Group entered into a collaboration, development and license agreement with Tesaro, under which the Group obtained an exclusive license for certain patents and know-how that Tesaro licensed from Merck, Sharp & Dohme Corp. (a subsidiary of Merck & Co. Inc.), or Merck Corp., and AstraZeneca UK Limited to develop, manufacture, use, sell, import and commercialize Tesaro’s proprietary PARP inhibitor, niraparib, in mainland China, Hong Kong and Macau, or the licensed territory, in the licensed field of treatment, diagnosis and prevention of any human diseases or conditions (other than prostate cancer). Tesaro has the option to elect to co-promote the licensed products in the Group’s licensed territory.

Under the terms of the agreement, the Group made an upfront payment of $15.0 million to Tesaro which was recorded as a research and development expense in 2016. If the Group successfully develops and commercializes the licensed products, the Group will make a milestone payment to Tesaro for the achievement of a certain development milestone event. In addition, if Tesaro does not exercise its co-promotion option, the Group will pay Tesaro milestone payments for the achievement of certain sales milestone events, and also tiered royalties at certain percentages of net sales of the licensed products, until the later of the expiration of the last-to-expire licensed patent covering the licensed product, the expiration of regulatory exclusivity for the licensed product, or the tenth anniversary of the first commercial sale of the licensed product, in each case on a product-by-product and region-by-region basis.

The Group has the right to terminate this agreement by providing Tesaro with prior written notice.

License and collaboration agreement with GlaxoSmithKline (China) R&D Co., Ltd (“GSK China”)

In October 2016, the Group entered into a license and transfer agreement with GSK China, an affiliate of GSK, under which GSK China transferred to the Group its rights under certain patents, know-how, inventory and regulatory materials to develop, manufacture, use and commercialize FUGAN and GRAPE, two formulations comprising extracts from traditional Chinese herbs, for the treatment, diagnosis and prevention of human diseases. In connection with such transfer, GSK China also assigned to the Group its agreements with Chengdu Bater Pharmaceutical Co., Ltd, or Bater, and Traditional Chinese Medical Hospital, Xinjiang Medical University, or Xinjiang, relating to FUGAN and GRAPE.

Under the terms of the agreement, the Group made an upfront payment to GSK China of $0.7 million (RMB4.5 million) which was recorded as a research and development expense in 2016. The Group made a milestone payment of $0.3 million (RMB2.0 million) to Bater for the achievement of milestone by enrolling the first patient in a Phase II Clinical Trial of the Product in 2017. The Group will make further milestone payments to GSK China for the achievement of certain development milestone events. In addition, the Group will pay to GSK China tiered royalties at certain percentage rates on the net sales of FUGAN and GRAPE. The Group also assumed the obligation to make milestone payments under the assigned agreements with Bater and Xinjiang for milestones achieved after the assignment of the agreements to the Group.

If the Group sublicenses, sells or otherwise divests the patents and know-how acquired from GSK China to third parties before the completion of a certain development phase, the Group is also required to pay to GSK China a share of its income attributed to such sublicense, sale, or divesture.

The Group may not terminate the agreement before the completion of the Phase II Study of FUGAN unless for causes beyond the reasonable control of the Group. Subject to the completion of the Phase II Study of FUGAN, the Group has the right to terminate the agreement upon prior written consent.

License and collaboration agreement with Paratek Bermuda Ltd. (“Paratek”)

In April 2017, the Group entered into a collaboration, development and license agreement with Paratek, under which the Group obtained both an exclusive license under certain patents and know-how of Paratek and an exclusive sub-license under certain intellectual property that Paratek licensed from Tufts University to develop, manufacture, use, sell, import and commercialize omadacycline in mainland China, Hong Kong, Macau and Taiwan, or licensed territory, in the field of all human therapeutic and preventative uses other than biodefense, or the licensed field. Paratek retains the right to manufacture the licensed product in the licensed territory for use outside the licensed territory. The Group also granted to Paratek a non-exclusive license to certain of intellectual property for Paratek Bermuda Ltd.

Under the terms of the agreement, the Group made an upfront payment of $7.5 million to Paratek which was recorded as a research and development expense in 2017. The Group will make a milestone payment to Paratek for the achievement of certain development milestone and sales milestone event. In addition, we will pay to Paratek tiered royalties at certain percentage rates on the net sales of licensed products, until the later of the abandonment, expiration or invalidation of the last-to-expire licensed patent covering the licensed product, or the eleventh anniversary of the first commercial sale of the licensed product, in each case on a product-by-product and region-by-region basis.

The Group has the right to terminate this agreement for any or no reason by providing Paratek with prior written notice with no penalty.

License and collaboration agreement with Five Prime Therapeutics, Inc. (“Five Prime”)

On December 19, 2017, the Group and Five Prime entered into an exclusive license agreement for FPA144 in Greater China and global strategic development collaboration.

Under the terms of the agreement, Five Prime has granted the Group an exclusive license to develop and commercialize FPA144 in the Greater China territory: China, Hong Kong, Macau, and Taiwan. The Group will be responsible for conducting the Phase 3 FIGHT trial in Greater China, including screening, enrolment and treatment of patients, and for commercialization of FPA144 in the Greater China territory. Five Prime will manufacture and supply FPA144 for the study. A Joint Steering Committee will be formed between the companies to oversee development, regulatory and commercialization activities in greater China.

The Group paid upfront fee of $5.0 million in January 2018, and will make milestone payments of $39.0 million for the achievement of certain development and regulatory milestones to Five Prime. In addition, the Group will pay to Five Prime a royalty percentage on net sales of FPA144 in Greater China ranging from the high teens to the low twenties. Given the strategic importance of China to the development and commercialization of FPA144 and to align the interests of the two companies globally, the Group is also eligible to receive a low single-digit royalty from Five Prime on net sales of FPA144 outside of Greater China.

The Group has the right to terminate this agreement at any time by providing written notice of termination to Five Prime.

As noted above, the Group has entered into various license and collaboration agreements with third party licensors to develop and commercialize drug candidates. Based on the terms of these agreements the Group is contingently obligated to make additional material payments upon the achievement of certain contractually defined milestones. The Group made $0.3 million milestone payment under these agreements for the years ended December 31, 2017. Based on management’s evaluation of the progress of each project noted above, the licensors will be eligible to receive from the Group up to an aggregate of approximately $400.8 million in future milestone payments upon the achievement of contractually specified development milestones, such as regulatory approval for the drug candidates, which may be before the Group has commercialized the drug or received any revenue from sales of such drug candidate, which may never occur.

Restricted Net Assets

12 Months Ended

Dec. 31, 2017

Restricted Net Assets [Abstract]

Restricted net assets

14.	Restricted net assets

The Group's ability to pay dividends may depend on the Group receiving distributions of funds from its PRC subsidiary. Relevant PRC statutory laws and regulations permit payments of dividends by the Group's PRC subsidiary only out of its retained earnings, if any, as determined in accordance with PRC accounting standards and regulations. The results of operations reflected in the consolidated financial statements prepared in accordance with U.S. GAAP differ from those reflected in the statutory financial statements of the Group's PRC subsidiary.

In accordance with the Company law of the PRC, a domestic enterprise is required to provide statutory reserves of at least 10% of its annual after-tax profit until such reserve has reached 50% of its respective registered capital based on the enterprise's PRC statutory accounts. A domestic enterprise is also required to provide discretionary surplus reserve, at the discretion of the Board of Directors, from the profits determined in accordance with the enterprise's PRC statutory accounts. The aforementioned reserves can only be used for specific purposes and are not distributable as cash dividends. The Group's PRC subsidiary was established as domestic invested enterprise and therefore is subject to the above mentioned restrictions on distributable profits.

During the years ended December 31, 2016 and 2017, no appropriation to statutory reserves was made because the PRC subsidiary had substantial losses during such periods.

As a result of these PRC laws and regulations subject to the limit discussed above that require annual appropriations of 10% of after-tax income to be set aside, prior to payment of dividends, as general reserve fund, the Group's PRC subsidiary is restricted in their ability to transfer a portion of their net assets to the Group.

Foreign exchange and other regulation in the PRC may further restrict the Group's PRC subsidiary from transferring funds to the Group in the form of dividends, loans and advances. As of December 31, 2016 and 2017, amounts restricted are the paid-in capital of the Group's PRC subsidiaries, which amounted to $39,215,714 and $80,951,618, respectively.

Employee Defined Contribution Plan

12 Months Ended

Dec. 31, 2017

Compensation And Retirement Disclosure [Abstract]

Employee defined contribution plan

15.	Employee defined contribution plan

Full time employees of the Group in the PRC participate in a government mandated defined contribution plan, pursuant to which certain pension benefits, medical care, employee housing fund and other welfare benefits are provided to employees. Chinese labor regulations require that the Group's PRC subsidiary make contributions to the government for these benefits based on certain percentages of the employees' salaries. The Group has no legal obligation for the benefits beyond the contributions made. The total amounts for such employee benefits, which were expensed as incurred, were $79,878, $288,666 and $579,094 for the years ended December 31, 2015, 2016 and 2017, respectively.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

16.	Commitments and Contingencies

(a)	Operating lease commitments

The Group leases office facilities under operating leases expiring on different dates. Payments under operating leases are expensed on a straight-line basis over the periods of their respective leases, and the terms of the leases do not contain rent escalation, contingent rent, renewal, or purchase options.

There are no restrictions placed upon the Group by entering into these leases. Total expenses under these operating leases were $148,274, $285,742 and $916,612 for the years ended December 31, 2015, 2016 and 2017, respectively.

Future minimum lease payments under operating lease agreements at December 31, 2017 were as follows:

	Year ended December 31,
	$
2018		1,311,102
2019		1,302,945
2020		358,342
2021		53,692
2022 and thereafter		—
Total lease commitment		3,026,081

(b)	Purchase commitments

As of December 31, 2017, the Group’s commitments related to purchase of property and equipment contracted but not yet reflected in the consolidated financial statement was $4,926,073 which is expected to be incurred within one year.

(c)	Capital commitments

The Group’s total capital commitment to its underlying investment in JING is RMB 26.3 million ($3.9 million). As of December 31, 2017, the Group’s unfunded commitment to JING was RMB 13.2 million ($2.0 million).

(d)	Contingencies

The Group is a party to or assignee of license and collaboration agreements that may require it to make future payments relating to milestone fees and royalties on future sales of licensed products (Note 13).

Subsequent events

12 Months Ended

Dec. 31, 2017

Subsequent Events [Abstract]

Subsequent events

17.	Subsequent events

In first quarter of 2018, the Group granted 1,153,750 share options to certain management and employees of the Group at the exercise price ranging from $20.74 to $24.58 per share under the 2017 Plan. These options granted have a contractual term of 10 years and generally vest over a five year period, with 20% of the awards vesting on the anniversary date one year after the grant date.

On January 1, 2018, 37,500 ordinary shares were authorized for grant to the independent directors. The restricted shares shall vest and be released from the restrictions in full on the first anniversary from the date of the agreement.

On March 2, 2018, 100,000 ordinary shares were authorized for grant to certain management. One fifth of the restricted shares shall vest and be released from the restrictions on each yearly anniversary of the date of the agreement.

On March 29, 2018, the Group and Hanmi entered into the agreement to terminate the license and collaboration agreement between the Group and Hanmi. No payment is due from one party to another and the Group has no accrued payment obligation to Hanmi as of the effective date of termination thereafter.

On April 25, 2018, the Group entered into a license and collaboration agreement with Entasis Therapeutics Holdings Inc.(“Entasis”), under which the Group obtained an exclusive right to develop and commercialize Entasis’s broad-spectrum intravenous inhibitor of β-lactamases or ETX2514 in the Asia-Pacific region for the treatment of a variety of serious multidrug-resistant infections caused by Acinetobacter baumannii. The Group is obligated to pay $5.0 million non-refundable upfront fees to Entasis upon entering the agreement and is contingently obligated to make future milestone payments upon the achievement of contractually specified development milestones.

Financial Statements Schedule I

12 Months Ended

Dec. 31, 2017

Condensed Financial Information Of Parent Company Only Disclosure [Abstract]

Financial Statements Schedule I

Additional financial information of parent company -

Financial statements schedule I

Zai Lab Limited

Financial information of parent company

Condensed balance sheets

(In U.S. dollars ("$") except for number of shares)

	As of December 31,
	2016			2017
	$			$
Assets
Current assets:
Cash and cash equivalents		24,813,050			181,910,618
Prepayments and other current assets		—			450,333
Total current assets		24,813,050			182,360,951
Investment in subsidiaries		62,042,345			54,885,326
Total assets		86,855,395			237,246,277
Liabilities, mezzanine equity and shareholders' deficits
Liabilities
Current liabilities:
Warrant liabilities		3,900,000			—
Other payables		—			593,317
Total current liabilities		3,900,000			593,317
Deferred income		—			1,482,000
Total liabilities		3,900,000			2,075,317
Mezzanine equity
Series A1 convertible preferred shares (par value US$0.00006 per share; 8,466,667 shares authorized, 8,466,665 shares issued and outstanding as of December 31, 2016)		10,028,572			—
Series A2 convertible preferred shares (par value US$0.00006 per share; 8,904,032 shares authorized, 8,442,221 shares issued and outstanding as of December 31, 2016)		18,278,572			—
Series B1 convertible preferred shares (par value US$0.00006 per share; 5,562,337 shares authorized, 5,562,335 shares issued and outstanding as of December 31, 2016)		53,100,000			—
Series B2 convertible preferred shares (par value US$0.00006 per share; 3,973,098 shares authorized, 3,973,096 shares issued and outstanding as of December 31, 2016)		53,100,000			—
Total mezzanine equity		134,507,144			—
Shareholders' (deficit) equity
Ordinary shares (par value of US$0.00006 per share; 83,333,333 shares authorized, 9,657,175 and 49,912,570 shares outstanding as of December 31, 2016 and 2017, respectively)		579			2,995
Subscription receivable		(5	)		(18	)
Additional paid-in capital		9,313,646			345,269,688
Accumulated deficit		(60,167,437	)		(110,551,613	)
Additional other comprehensive (loss) income		(698,532	)		449,908
Total shareholders' (deficit) equity		(51,551,749	)		235,170,960
Total liabilities, mezzanine equity and shareholders' (deficit) equity		86,855,395			237,246,277

Additional financial information of parent company -

Financial statements schedule I

Zai Lab Limited

Financial information of parent company

Condensed statements of operations and comprehensive loss

(In U.S. dollars ("$") except for number of shares)

	Year Ended December 31,
	2015			2016			2017
	$			$			$
Operating Expenses:
General and administrative		(56,806	)		(534,660	)		(4,114,144	)
Loss from operations		(56,806	)		(534,660	)		(4,114,144	)
Interest income		—			—			50,060
Changes in fair value of warrants		(1,980,000	)		(1,920,000	)		200,000
Equity in loss of subsidiaries		(15,984,931	)		(35,057,552	)		(46,598,092	)
Other income		—			—			78,000
Loss before income tax		(18,021,737	)		(37,512,212	)		(50,384,176	)
Income tax expense		—			—			—
Net loss attributable to ordinary shareholders		(18,021,737	)		(37,512,212	)		(50,384,176	)
Net loss		(18,021,737	)		(37,512,212	)		(50,384,176	)
Other comprehensive (loss) income, net of tax of nil:
Foreign currency translation adjustment		(98,893	)		(594,912	)		1,148,440
Comprehensive loss		(18,120,630	)		(38,107,124	)		(49,235,736	)

Additional financial information of parent company -

Financial statements schedule I

Zai Lab Limited

Financial information of parent company

Condensed statements of cash flows

(In U.S. dollars ("$") except for number of shares)

	Year Ended December 31,
	2015			2016			2017
	$			$			$
Cash flows from Operating activities:
Net loss		(18,021,737	)		(37,512,212	)		(50,384,176	)
Adjustments to reconcile net loss to net cash provided by operating activities:
Share based compensation		56,806			534,660			3,346,039
Change of fair value of warrants		1,980,000			1,920,000			(200,000	)
Equity in loss of subsidiaries		15,984,931			35,057,552			46,598,092
Changes in operating assets and liabilities:
Prepayments and other current assets		—			—			(450,333	)
Other payables		—			—			553,317
Deferred income		—			—			1,482,000
Net cash provided by operating activities		—			—			944,939

Cash flows from investing activities:
Investment in subsidiaries		(21,500,000	)		(84,501,020	)		(31,707,566	)
Net cash used in investing activities		(21,500,000	)		(84,501,020	)		(31,707,566	)

Cash flows from financing activities:
Proceed from issuance of convertible preferred shares, net of issuance cost		18,278,572			106,200,000			29,100,000
Proceeds from exercise of warrants		—			—			1,000,000
Proceeds from exercises of stock options		—			—			65,500
Proceeds from issuance of ordinary shares upon initial public offering		—			—			160,424,994
Payment of initial public offering costs		—			—			(2,730,299	)
Net cash provided by financing activities		18,278,572			106,200,000			187,860,195

Effect of foreign exchange rate changes on cash and cash equivalent		—			—			—

Net (decrease) increases in cash and cash equivalents		(3,221,428	)		21,698,980			157,097,568
Cash and cash equivalents-beginning of the year		6,335,498			3,114,070			24,813,050
Cash and cash equivalents-end of the year		3,114,070			24,813,050			181,910,618

Additional financial information of parent company -

Financial statements schedule I

Zai Lab Limited

Financial information of parent company

Notes to schedule I

(In U.S. dollars ("$") except for number of shares)

1. Schedule I has been provided pursuant to the requirements of Rule 12-04(a) and 5-04(c) of Regulation S-X, which require condensed financial information as to the financial position, changes in financial position and results of operations of a parent company as of the same dates and for the same periods for which audited consolidated financial statements have been presented when the restricted net assets of consolidated subsidiaries exceed 25 percent of consolidated net assets as of the end of the most recently completed fiscal year.

2. The condensed financial information has been prepared using the same accounting policies as set out in the consolidated financial statements except that the equity method has been used to account for investments in its subsidiaries. For the parent company, the Company records its investments in subsidiaries under the equity method of accounting as prescribed in ASC 323, Investments-Equity Method and Joint Ventures. Such investments are presented on the Condensed Balance Sheets as ‘‘Investment in subsidiaries’’. Ordinarily under the equity, an investor in an equity method investee would cease to recognize its share of the losses of an investee once the carrying value of the investment has been reduced to nil absent an undertaking by the investor to provide continuing support and fund losses. For the purpose of this Schedule I, the parent company has continued to reflect its share, based on its proportionate interest, of the losses of subsidiaries regardless of the carrying value of the investment even though the parent company is not obligated to provide continuing support or fund losses.

3. As of December 31, 2016 and 2017, there were no material contingencies, significant provisions of long term obligations, mandatory dividend or redemption requirements of redeemable stocks or guarantees of the Company.

- Definition

The entire disclosure for condensed financial information, including the financial position, cash flows, and the results of operations of the registrant (parent company) as of the same dates or for the same periods for which audited consolidated financial statements are being presented. Alternatively, the details of this disclosure can be reported by the specific parent company taxonomy elements, indicating the appropriate date and period contexts in an instance document.

+ References + Details

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of presentation

(a) Basis of presentation

The consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP").

Principles of consolidation

(b) Principles of consolidation

Use of estimates

Foreign currency translation

(d) Foreign currency translation

Cash and cash equivalents

(e) Cash and cash equivalents

Investments in equity investees

(f) Investments in equity investees

Prepayments for equipment

(g) Prepayments for equipment

The prepayments for equipment purchase are recorded in long term prepayments considering the prepayments are all related to property and equipment.

Property and equipment

(h) Property and equipment

		Useful life
Office equipment		3 years
Electronic equipment		3 years
Vehicle		4 years
Laboratory equipment		5 years
Manufacturing equipment		10 years
Leasehold improvements		lesser of useful life or lease term

Construction in progress represents property and equipment under construction and pending installation and is stated at cost less impairment losses if any.

Long term deposits

(i) Long term deposits

Long term deposits represent amounts paid in connection with the Group’s long-term lease agreements.

Value added tax recoverable

(j) Value added tax recoverable

Intangible assets

(k) Intangible assets

Impairment of long-lived assets

(l) Impairment of long-lived assets

Fair value measurements

(m) Fair value measurements

ASC 820 establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1 - Observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets.

Level 2 - Include other inputs that are directly or indirectly observable in the marketplace.

Level 3 - Unobservable inputs which are supported by little or no market activity.

Liabilities measured at fair value on a recurring basis as of December 31, 2016 are summarized below:

	Level 1		Level 2		Level 3
	$		$		$
Warrant liabilities		—		—		3,900,000

The Group has measured the warrant liabilities at fair values on a recurring basis using significant unobservable inputs (Level 3) as of the years ended December 31, 2016.

The Group used the binomial model to estimate the fair value of warrant liabilities using the following assumptions:

	December 31, 2016
Risk-free rate of return		2.9	%
Vesting date	April 1, 2016
Maturity date	December 31, 2021
Estimated volatility rate		70	%
Exercise price		2.16
Fair value of underlying preferred shares		9.84

Revenue recognition

(n) Revenue recognition

The Group has not yet generated any revenues from the sale of goods or from the rendering of services.

Research and development expenses

(o) Research and development expenses

Deferred income

(p) Deferred income

Deferred income consists of deferred income from government grants and American Depositary Receipts (the "ADR") Program Agreement with ADR depositary bank (the “DB”) in July 2017.

Leases

(q) Leases

Comprehensive loss

(r) Comprehensive loss

Stock-based compensation

(s) Stock-based compensation

Awards granted to employees

The Group grants share options to eligible employees, management and directors and accounts for these share based awards in accordance with ASC 718, Compensation-Stock Compensation.

To the extent the required vesting conditions are not met resulting in the forfeiture of the share-based awards, previously recognized compensation expense relating to those awards are reversed.

Awards granted to non-employees

Income taxes

(t) Income taxes

Earnings (Loss) per share

(u) Earnings (loss) per share

Basic earnings (loss) per ordinary share is computed by dividing net income (loss) attributable to ordinary shareholders by weighted average number of ordinary shares outstanding during the period.

Segment information

(v) Segment information

Concentration of risks

(w) Concentration of risks

Concentration of suppliers

The following suppliers accounted for 10% or more of research and development expenses for the years ended December 31, 2015, 2016 and 2017:

	Year ended December 31,
	2015		2016		2017
	$		$		$
A		5,703,000	*		*
B	*			14,625,500	*
C	*		*			7,651,617
D	*		*			7,104,015

*	Represents less than 10% of research and development expenses for the years ended December 31, 2015, 2016 and 2017.

Concentration of credit risk

Foreign currency risk

Share consolidation (“reverse stock split”)

(x) Share consolidation (“reverse stock split”)

Recent accounting pronouncements

(y) Recent accounting pronouncements

The Group is in a development stage, with no revenues to date.

Organization and Principal Activities (Tables)

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Significant Operating Subsidiaries

As of December 31, 2017, the Group's significant operating subsidiaries are as follows:

Name of company	Place of incorporation	Date of incorporation	Percentage of ownership	Principal activities
Zai Lab (Hong Kong) Limited	Hong Kong	April 29, 2013	100%	Operating company for business development and R&D activities
Zai Lab (Shanghai) Co., Ltd.	The People's Republic of China ("PRC" or "China")	January 6, 2014	100%	Development and commercialisation of innovative medicines
Zai Lab (AUST) Pty., Ltd.	Australia	December 10, 2014	100%	Clinical trial activities
Zai Lab (Suzhou) Co., Ltd.	PRC	November 30, 2015	100%	Development and commercialisation of innovative medicines
Zai Biopharmaceutical (Suzhou) Co., Ltd.	PRC	June 15, 2017	100%	Development and commercialisation of innovative medicines

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Estimated Useful Lives of Property and Equipment

Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets as follows:

		Useful life
Office equipment		3 years
Electronic equipment		3 years
Vehicle		4 years
Laboratory equipment		5 years
Manufacturing equipment		10 years
Leasehold improvements		lesser of useful life or lease term

Liabilities Measured at Fair Value on Recurring Basis

Liabilities measured at fair value on a recurring basis as of December 31, 2016 are summarized below:

	Level 1		Level 2		Level 3
	$		$		$
Warrant liabilities		—		—		3,900,000

Binomial Model Assumptions to Estimate Fair Value of Warrant Liabilities

The Group used the binomial model to estimate the fair value of warrant liabilities using the following assumptions:

	December 31, 2016
Risk-free rate of return		2.9	%
Vesting date	April 1, 2016
Maturity date	December 31, 2021
Estimated volatility rate		70	%
Exercise price		2.16
Fair value of underlying preferred shares		9.84

Suppliers Accounted for 10% or More of Research and Development Expenses

The following suppliers accounted for 10% or more of research and development expenses for the years ended December 31, 2015, 2016 and 2017:

	Year ended December 31,
	2015		2016		2017
	$		$		$
A		5,703,000	*		*
B	*			14,625,500	*
C	*		*			7,651,617
D	*		*			7,104,015

- Definition

Tabular disclosure of all significant concentrations of risk, including credit risk and market risk, arising from all financial instruments (as defined), whether from an individual counterparty or groups of counterparties. The disclosure concerning concentrations of risk may consist of the following information: (1) for concentrations of credit risk disclosure may include: (a) information about the (shared) activity, region, or economic characteristic that identifies the concentration, (b) the maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity, (c) the policy of requiring collateral or other security to support financial instruments subject to credit risk, information about the entity's access to that collateral or other security, and the nature and a brief description of the collateral or other security supporting those financial instruments, and (d) the policy of entering into master netting arrangements to mitigate the credit risk of financial instruments, information about the arrangements for which the entity is a party, and a brief description of the terms of those arrangements, including the extent to which they would reduce the entity's maximum amount of loss due to credit risk and (2) for disclosure of quantitative information about the market risks of financial instruments that is consistent with the way the company manages or adjusts those risks, disclosure may include: (a) more details about current positions and perhaps activity during the period, (b) the hypothetical effects on comprehensive income (or net assets), or annual income, of several possible changes in market prices, (c) a gap analysis of interest rate re-pricing or maturity dates, (d) the duration of the financial instruments, (e) the entity's value at risk from derivatives and from other positions at the end of the reporting period and the average value at risk during the year, or (f) other ways of reporting quantitative information as internally developed.

+ References + Details

Cash and Cash Equivalents (Tables)

12 Months Ended

Dec. 31, 2017

Cash And Cash Equivalents [Abstract]

Summary of Cash and Cash Equivalents

	As of December 31,
	2016		2017
	$		$
Cash at bank and in hand		36,531,272		204,008,828
Cash equivalents		47,417,498		25,651,320
		83,948,770		229,660,148
Denominated in:
US$		77,463,141		224,878,393
RMB (note (i))		6,365,311		3,927,163
Australia dollar ("A$")		120,318		854,592
		83,948,770		229,660,148

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consist of the following:

	As of December 31,
	2016			2017
	$			$
Office equipment		49,432			273,339
Electronic equipment		66,271			160,772
Vehicle		76,636			81,360
Laboratory equipment		593,582			1,686,133
Manufacturing equipment		—			2,832,726
Leasehold improvements		465,428			3,227,150
Construction in progress		252,509			4,252,894
		1,503,858			12,514,374
Less: accumulated depreciation		(257,800	)		(660,610	)
Property and equipment, net		1,246,058			11,853,764

Income Tax (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Loss Before Income Taxes

Loss before income taxes consists of:

	Year ended December 31,
	2015		2016		2017
	$		$		$
Cayman		2,036,806		2,454,660		3,886,673
BVI		—		—		8,375
PRC		4,938,688		26,111,094		40,971,742
HK		9,869,007		8,010,908		6,240,462
AUST		1,177,236		935,550		(723,076	)
		18,021,737		37,512,212		50,384,176

Schedule of Reconciliations of PRC Statutory Income Tax Rate and Group's Effective Income Tax Rate

Reconciliations of the differences between the PRC statutory income tax rate and the Group’s effective income tax rate for the years ended December 31, 2015, 2016 and 2017 are as follows:

	Year ended December 31,
	2015			2016			2017
	$			$			$
Statutory income tax rate		25	%		25	%		25	%
Share-based compensations		(3.68	%)		(2.92	%)		(3.27	%)
Non-deductible expenses		(7.19	%)		(1.59	%)		(0.79	%)
Effect of different tax rate of subsidiary operation in other jurisdictions		(7.15	%)		(3.33	%)		(3.06	%)
Changes in valuation allowance		(6.98	%)		(17.16	%)		(17.88	%)
Effective income tax rate		—			—			—

Schedule of Components of Deferred Tax Assets and Liabilities

The principal components of the deferred tax assets and liabilities are as follows:

	Year ended December 31,
	2015			2016			2017
	$			$			$
Deferred tax assets:
Depreciation of property and equipment, net		2,415			3,892			5,964
Accrued expenses		72,408			—			—
Government grants		16,025			166,336			187,762
Net operating loss forwards		1,729,009			8,086,361			17,075,387
Less: valuation allowance		(1,819,857	)		(8,256,589	)		(17,269,113	)
Deferred tax assets, net		—			—			—

Schedule of Movement of Valuation Allowance

Movement of the valuation allowance is as follows:

	2016			2017
	$			$
Balance as of January 1,		(1,819,857	)		(8,256,589	)
Additions		(6,436,732	)		(9,012,524	)
Balance as of December 31,		(8,256,589	)		(17,269,113	)

Other Payables (Tables)

12 Months Ended

Dec. 31, 2017

Other Liabilities Current [Abstract]

Schedule of Other Payables

	As of December 31,
	2016		2017
	$		$
Payroll		573,802		1,607,740
Professional service fee		23,721		714,764
Payables for purchase of property and equipment		—		413,657
Other taxes payable		—		17,793
Others		152,595		347,505
		750,118		3,101,459

Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Loss Per Share

Basic and diluted net loss per share for each of the years presented are calculated as follow:

	For the year ended December 31,
	2015			2016			2017
Numerator:
Net loss attributable to ordinary shareholders		(18,021,737	)		(37,512,212	)		(50,384,176	)
Denominator:
Weighted average number of ordinary shares- basic and diluted		8,693,655			9,439,028			21,752,757
Net loss per share-basic and diluted		(2.07	)		(3.97	)		(2.32	)

Summary of Anti-Dilutive Shares Excluded from Calculation of Diluted Loss Per Share

	As of December 31,
	2015		2016		2017
Number of Series A1 Shares outstanding		8,466,665		8,466,665		—
Number of Series A2 Shares outstanding		8,442,221		8,442,221		—
Number of Series B1 Shares outstanding		—		5,562,335		—
Number of Series B2 Shares outstanding		—		3,973,096		—
Share options		4,309,232		7,228,141		6,548,377
Non-vested restricted shares		2,948,148		2,309,490		693,333
Warrants		461,808		461,808		—

Related Party Transactions (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Major Related Party and Relationship

The table below sets forth the major related party and the relationship with the Group as of December 31, 2017:

Company Name		Relationship with the Group
Quan Venture Fund I, L.P.		Significantly influenced by Samantha Du, founder, chairman and CEO of the Company

Qiagen (Suzhou) Translational Medicine Co., Ltd.		Significant influence held by Samantha Du’s immediate family

Schedule of Transactions Between Related Party

The Group paid expenditures to its related party:

Research and development expenditures	Year ended December 31,
	2015		2016		2017
	$		$		$
Qiagen (Suzhou) Translational Medicine Co. Ltd.		96,656		—		—

Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Assumptions Used to Estimate Fair Values of Share Options Granted

The following table presents the assumptions used to estimate the fair values of the share options granted in the years presented:

	March 2015			October 2015			March 2016			August 2016			December 2016			May 2017			September 2017
Risk-free rate of return		3.1	%		3.1	%		2.8	%		2.5	%		3.4	%		3.2	%		3.5	%
Contractual life of option	10 years			10 years			10 years			10 years			10 years			10 years			10 years
Estimated volatility rate		70	%		70	%		70	%		70	%		70	%		70	%		70	%
Expected dividend yield		0	%		0	%		0	%		0	%		0	%		0	%		0	%
Fair value of underlying ordinary shares		1.62			1.92			7.14			8.04			8.04			9.60			27.93

Summary of Option Activity

A summary of option activity under the Plan during the years ended December 31, 2015, 2016 and 2017 is presented below:

	Number of options			Weighted average exercise price		Weighted average remaining contractual term		Aggregate intrinsic value
				$		Years		$
Outstanding at January 1, 2015		—			—		—		—
Granted		4,309,232			0.60		—		—
Outstanding at December 31, 2015		4,309,232			0.60		9.68		18,874,438
Granted		2,918,993			1.53		—		—
Forfeited		(84	)		1.74		—		—
Outstanding at December 31, 2016		7,228,141			0.97		9.00		53,677,170
Granted		264,480			8.76		—		—
Exercised		(100,834	)		0.65		—		—
Forfeited		(843,410	)		1.11		—		—
Outstanding at December 31, 2017		6,548,377			1.28		8.06		130,668,851
Vested and Exercisable as of December 31, 2017		2,307,319			0.80		7.84		47,134,503
Vested or expected to vest as of December 31, 2017		6,548,377			1.28		8.06		130,668,851

Allocation of Compensation Expense Related to Option

	Year ended December 31,
	2015		2016		2017
	$		$		$
General and administrative		124,871		1,472,993		2,215,282
Research and development		294,838		2,051,740		2,536,651
Total		419,709		3,524,733		4,751,933

Summary of Non-vested Restricted Share Activity

The following table summarized the Group’s non-vested restricted share activity in 2017:

	Numbers of non-vested restricted shares			Weighted average grant date fair value
				$
Non-vested as of January 1, 2017		2,309,490			1.31
Granted		50,000			27.93
Vested		(2,309,490	)		1.03
Transferred from Red Kingdom		643,333			0.60
Non-vested as of December 31, 2017		693,333			2.57

Allocation of Compensation Expense Related to Restricted Shares

	Year ended December 31,
	2015		2016		2017
	$		$		$
General and administrative		964,012		825,822		3,848,165
Research and development		1,317,683		574,723		1,331,008
Total		2,281,695		1,400,545		5,179,173

Red Kingdom

Summary of Non-vested Restricted Share Activity

The following table summarized the non-vested restricted shares activities of Red Kingdom in 2017:

	Numbers of non-vested restricted shares			Weighted average grant date fair value
				$
Non-vested as of January 1, 2017		2,784,999			0.60
Vested		(811,667	)		0.60
Forfeited		(1,329,999	)		0.60
Transferred to the Company		(643,333	)		0.60
Non-vested as of December 31, 2017		—

Accumulated Other Comprehensive Loss (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Summary of Accumulated Other Comprehensive Loss

The movement of accumulated other comprehensive loss is as follows:

	Foreign currency translation adjustments
	$
Balance as of January 1, 2015		(4,727	)
Other comprehensive loss		(98,893	)
Balance as of December 31, 2015		(103,620	)
Other comprehensive loss		(594,912	)
Balance as of December 31, 2016		(698,532	)
Other comprehensive income		1,148,440
Balance as of December 31, 2017		449,908

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Agreements

Future minimum lease payments under operating lease agreements at December 31, 2017 were as follows:

	Year ended December 31,
	$
2018		1,311,102
2019		1,302,945
2020		358,342
2021		53,692
2022 and thereafter		—
Total lease commitment		3,026,081

Organization and Principal Activities - Schedule of Significant Operating Subsidiaries (Details)	12 Months Ended
	Dec. 31, 2017
Zai Lab (Hong Kong) Limited
Subsidiary Of Limited Liability Company Or Limited Partnership [Line Items]
Place of incorporation	Hong Kong
Date of incorporation	Apr. 29, 2013
Percentage of ownership	100.00%
Principal activities	Operating company for business development and R&D activities
Zai Lab (Shanghai) Co., Ltd
Subsidiary Of Limited Liability Company Or Limited Partnership [Line Items]
Place of incorporation	The People's Republic of China ("PRC" or "China")
Date of incorporation	Jan. 06, 2014
Percentage of ownership	100.00%
Principal activities	Development and commercialisation of innovative medicines
Zai Lab (AUST) Pty., Ltd
Subsidiary Of Limited Liability Company Or Limited Partnership [Line Items]
Place of incorporation	Australia
Date of incorporation	Dec. 10, 2014
Percentage of ownership	100.00%
Principal activities	Clinical trial activities
Zai Lab (Suzhou) Co., Ltd
Subsidiary Of Limited Liability Company Or Limited Partnership [Line Items]
Place of incorporation	PRC
Date of incorporation	Nov. 30, 2015
Percentage of ownership	100.00%
Principal activities	Development and commercialisation of innovative medicines
Zai Biopharmaceutical (Suzhou) Co., Ltd
Subsidiary Of Limited Liability Company Or Limited Partnership [Line Items]
Place of incorporation	PRC
Date of incorporation	Jun. 15, 2017
Percentage of ownership	100.00%
Principal activities	Development and commercialisation of innovative medicines

Summary of Significant Accounting Policies - Additional Information (Details)			12 Months Ended
	Aug. 30, 2017	Apr. 01, 2016 USD ($)	Dec. 31, 2017 USD ($) Segment shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 CNY (¥) shares	Jul. 19, 2017 shares	Dec. 31, 2016 CNY (¥)	Dec. 31, 2014 USD ($)
Significant Accounting Policies [Line Items]
Impairment of investments			$ 0	$ 0	$ 0
Externally purchased software, amortization period			5 years
Original value of intangible assets			$ 24,377	8,684
Accumulated amortization			4,288	1,684
Impairment of long-lived assets			$ 0	$ 0	0
Investment threshold amount		$ 7,000,000
Vesting date		Apr. 01, 2016		Apr. 01, 2016
Maturity period stated in terms			6 years
Cash grants recorded in other income			$ 855,158	$ 2,065,510	298,072
Cash grants recorded in deferred income			$ 912,124	778,434
Reimbursement recognized period			5 years
Capital leases			$ 0	0	0
Unrecognized tax benefits and related interest and penalties			$ 0	0	0
Number of reportable segments \| Segment			1
Aggregate amount of cash and cash equivalents			$ 229,660,148	$ 83,948,770	$ 13,160,696				$ 7,152,274
Share consolidation of ordinary shares and preferred shares	six-to-one
ASU 2016-02
Significant Accounting Policies [Line Items]
Unrecognized future minimum operating lease commitments			$ 3,000,000
Cash and Cash Equivalents
Significant Accounting Policies [Line Items]
Percentage of foreign currency risk			2.00%	8.00%
Foreign Currency Risk \| Cash and Cash Equivalents
Significant Accounting Policies [Line Items]
Aggregate amount of cash and cash equivalents \| ¥						¥ 25,660,869		¥ 44,156,161
Deferred Income
Significant Accounting Policies [Line Items]
Reimbursements recognized			$ 1,482,000
Other Income
Significant Accounting Policies [Line Items]
Reimbursements recognized			$ 78,000
Series A2 Convertible Preferred Shares
Significant Accounting Policies [Line Items]
Issuance warrants to purchase preferred shares \| shares			461,808			461,808	461,808

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Office Equipment
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Electronic Equipment
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Vehicle
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	4 years
Laboratory Equipment
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	5 years
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	10 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	lesser of useful life or lease term

Summary of Significant Accounting Policies - Liabilities Measured at Fair Value on Recurring Basis (Details)	Dec. 31, 2016 USD ($)
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrant liabilities	$ 3,900,000

Summary of Significant Accounting Policies - Binomial Model Assumptions to Estimate Fair Value of Warrant Liabilities (Details) - $ / shares		12 Months Ended
	Apr. 01, 2016	Dec. 31, 2016
Accounting Policies [Abstract]
Risk-free rate of return		2.90%
Vesting date	Apr. 01, 2016	Apr. 01, 2016
Maturity date		Dec. 31, 2021
Estimated volatility rate		70.00%
Exercise price		$ 2.16
Fair value of underlying preferred shares		$ 9.84

Summary of Significant Accounting Policies - Suppliers Accounted for 10% or More of Research and Development Expenses (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Accounting Policies [Line Items]
Research and development expenses	$ 39,341,518	$ 32,149,157	$ 13,587,145
Research and Development Expenses \| Concentration of Suppliers \| A
Significant Accounting Policies [Line Items]
Research and development expenses			$ 5,703,000
Research and Development Expenses \| Concentration of Suppliers \| B
Significant Accounting Policies [Line Items]
Research and development expenses		$ 14,625,500
Research and Development Expenses \| Concentration of Suppliers \| C
Significant Accounting Policies [Line Items]
Research and development expenses	7,651,617
Research and Development Expenses \| Concentration of Suppliers \| D
Significant Accounting Policies [Line Items]
Research and development expenses	$ 7,104,015

Summary of Significant Accounting Policies - Suppliers Accounted for 10% or More of Research and Development Expenses (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Research and Development Expenses \| Concentration of Suppliers
Significant Accounting Policies [Line Items]
Concentration risk percentage	10.00%	10.00%	10.00%

Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash And Cash Equivalents [Line Items]
Cash at bank and in hand	$ 204,008,828	$ 36,531,272
Cash equivalents	25,651,320	47,417,498
Cash and cash equivalents	229,660,148	83,948,770	$ 13,160,696	$ 7,152,274
Denominated in US$
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	224,878,393	77,463,141
Denominated in RMB
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	3,927,163	6,365,311
Denominated in Australia dollar
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	$ 854,592	$ 120,318

Investment in Equity Investees - Additional Information (Details) ¥ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CNY (¥)	Jul. 05, 2017 USD ($)	Jul. 05, 2017 CNY (¥)	Jun. 30, 2017 USD ($) Investor	Jun. 30, 2017 CNY (¥) Investor	Oct. 31, 2016 USD ($)
Equity And Cost Method Investments [Line Items]
Cost method investments								$ 500,000
Quan Venture Fund I, L.P.
Equity And Cost Method Investments [Line Items]
Cash consideration for investment disposed	$ 500,000
Gain/loss recognized upon disposal	$ 0
JING
Equity And Cost Method Investments [Line Items]
Number of third-parties \| Investor						3	3
Capital contribution in cash				$ 1,900,000	¥ 13.1
Capital contribution commitment		$ 3,900,000	¥ 26.3			$ 3,900,000	¥ 26.3
Percentage of equity interest						20.00%	20.00%
Share of loss of investee		$ 249,652

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 12,514,374	$ 1,503,858
Less: accumulated depreciation	(660,610)	(257,800)
Property and equipment, net	11,853,764	1,246,058
Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	273,339	49,432
Electronic Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	160,772	66,271
Vehicle
Property Plant And Equipment [Line Items]
Property and equipment, gross	81,360	76,636
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,686,133	593,582
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,832,726
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,227,150	465,428
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4,252,894	$ 252,509

Property and Equipment - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Depreciation expenses	$ 545,705	$ 198,224	$ 125,774

Income Tax - Additional Information (Details) - USD ($)	12 Months Ended
Income Tax - Additional Information (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Taxable income	$ (50,384,176)	$ (37,512,212)	$ (18,021,737)
Provision for income taxes	0
Amounts of operating loss carry forwards	$ 72,137,289	$ 34,716,071	$ 7,969,098
PRC
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%	25.00%	25.00%
Taxable income	$ (40,971,742)	$ (26,111,094)	$ (4,938,688)
Earliest Tax Year
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration	Dec. 31, 2019
Latest Tax Year
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration	Dec. 31, 2022
Zai Lab (AUST) Pty., Ltd
Income Tax Disclosure [Line Items]
Statutory income tax rate	30.00%
Taxable income	$ 0	0	0
Provision for income taxes	$ 0	0	0
Zai Lab (Hong Kong) Limited
Income Tax Disclosure [Line Items]
Statutory income tax rate	16.50%
Taxable income	$ 0	0	0
Provision for income taxes	$ 0	$ 0	$ 0
Zai Lab (Shanghai) Co., Ltd
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%
Zai Lab (Suzhou) Co., Ltd
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%
Zai Biopharmaceutical (Suzhou) Co., Ltd
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%

Income Tax - Schedule of Loss Before Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Loss before income taxes	$ 50,384,176	$ 37,512,212	$ 18,021,737
Cayman
Income Tax Disclosure [Line Items]
Loss before income taxes	3,886,673	2,454,660	2,036,806
BVI
Income Tax Disclosure [Line Items]
Loss before income taxes	8,375
PRC
Income Tax Disclosure [Line Items]
Loss before income taxes	40,971,742	26,111,094	4,938,688
HK
Income Tax Disclosure [Line Items]
Loss before income taxes	6,240,462	8,010,908	9,869,007
AUST
Income Tax Disclosure [Line Items]
Loss before income taxes	$ (723,076)	$ 935,550	$ 1,177,236

Income Tax - Schedule of Reconciliations of PRC Statutory Income Tax Rate and Group's Effective Income Tax Rate (Details) - PRC	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Statutory income tax rate	25.00%	25.00%	25.00%
Share-based compensations	(3.27%)	(2.92%)	(3.68%)
Non-deductible expenses	(0.79%)	(1.59%)	(7.19%)
Effect of different tax rate of subsidiary operation in other jurisdictions	(3.06%)	(3.33%)	(7.15%)
Changes in valuation allowance	(17.88%)	(17.16%)	(6.98%)

Income Tax - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Depreciation of property and equipment, net	$ 5,964	$ 3,892	$ 2,415
Accrued expenses			72,408
Government grants	187,762	166,336	16,025
Net operating loss forwards	17,075,387	8,086,361	1,729,009
Less: valuation allowance	$ (17,269,113)	$ (8,256,589)	$ (1,819,857)

Income Tax - Schedule of Movement of Valuation Allowance (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Beginning Balance	$ (8,256,589)	$ (1,819,857)
Additions	(9,012,524)	(6,436,732)
Ending Balance	$ (17,269,113)	$ (8,256,589)

Other Payables - Schedule of Other Payables (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Other Liabilities Current [Abstract]
Payroll	$ 1,607,740	$ 573,802
Professional service fee	714,764	23,721
Payables for purchase of property and equipment	413,657
Other taxes payable	17,793
Others	347,505	152,595
Other payables, total	$ 3,101,459	$ 750,118

Convertible Preferred Shares and Warrants - Additional Information (Details)	1 Months Ended						12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017 USD ($) $ / shares shares	Apr. 30, 2016 USD ($) $ / shares shares	Jan. 31, 2016 USD ($) $ / shares shares	Apr. 30, 2015 USD ($) $ / shares shares	Aug. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) Investor $ / shares shares	Sep. 20, 2017 shares	Jul. 19, 2017 $ / shares shares	Apr. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)
Convertible Preferred Shares and Warrants [Line Items]
Cash proceeds from convertible preferred shares \| $							$ 29,100,000	$ 106,200,000	$ 18,278,572
Change in fair value of warrants \| $							$ (200,000)	1,920,000	1,980,000
Expected successful QIPO period							5 years
Warrant
Convertible Preferred Shares and Warrants [Line Items]
Warrants vesting period							Apr. 01, 2016
Warrant expiration prior date on consummates qualified initial public offering							90 days
A1, A2, B1, B2 and C Preferred Share
Convertible Preferred Shares and Warrants [Line Items]
Change in fair value of warrants \| $							$ (200,000)	$ 1,900,000	$ 2,000,000
Dividends entitled to preferred shareholders							8.00%
Beneficial conversion feature \| $							$ 0
A1, A2, B1, B2 and C Preferred Share \| IPO
Convertible Preferred Shares and Warrants [Line Items]
Number of ordinary shares issued upon conversion of preferred stock \| shares										28,905,083
Series A1 Convertible Preferred Shares
Convertible Preferred Shares and Warrants [Line Items]
Issued convertible preferred shares \| shares						6,244,443		8,466,665
Par value of issued convertible preferred shares						$ 0.00006		$ 0.00006
Cash proceeds from convertible preferred shares \| $						$ 8,028,572
Convertible preferred shares, price per share						$ 1.2857
Convertible loans issued \| $												$ 2,000,000	$ 2,000,000
Convertible loans converted into preferred shares \| shares						2,222,222
Convertible loans converted into preferred shares, price per share						$ 0.90
Series A2 Convertible Preferred Shares
Convertible Preferred Shares and Warrants [Line Items]
Issued convertible preferred shares \| shares					8,442,221			8,442,221
Par value of issued convertible preferred shares					$ 0.00006			$ 0.00006
Cash proceeds from convertible preferred shares \| $					$ 18,278,572
Convertible preferred shares, price per share					$ 2.1651
Number of warrant agreement \| Investor									1
Issuance warrants to purchase preferred shares \| shares							461,808				461,808
Issuance warrants to purchase preferred shares, price per share									$ 2.1651		$ 2.1651
Change in fair value of warrants \| $									$ 1,980,000
Series A2 Convertible Preferred Shares \| Maximum
Convertible Preferred Shares and Warrants [Line Items]
Issuance warrants to purchase preferred shares \| shares									461,808
Series B1 Convertible Preferred Shares
Convertible Preferred Shares and Warrants [Line Items]
Issued convertible preferred shares \| shares				5,562,335				5,562,335
Par value of issued convertible preferred shares				$ 0.00006				$ 0.00006
Cash proceeds from convertible preferred shares \| $				$ 53,100,000
Convertible preferred shares, price per share				$ 9.5464
Series B2 Convertible Preferred Shares
Convertible Preferred Shares and Warrants [Line Items]
Issued convertible preferred shares \| shares			3,973,096					3,973,096
Par value of issued convertible preferred shares			$ 0.00006					$ 0.00006
Cash proceeds from convertible preferred shares \| $			$ 53,100,000
Convertible preferred shares, price per share			$ 13.3649
Series C Preferred Shares
Convertible Preferred Shares and Warrants [Line Items]
Issued convertible preferred shares \| shares		1,998,958
Par value of issued convertible preferred shares		$ 0.00006
Cash proceeds from convertible preferred shares \| $		$ 30,000,000
Convertible preferred shares, price per share		$ 15.0078
Description of preferred share conversion rights							The initial conversion price shall equal the lower of (1) the issuance price of Series C Preferred Shares and (2) Calculated Price which is one hundred percent minus the discount rate of fifteen percent (the “Discount Rate”) multiplied by the offering price of the ordinary shares of the Company to the public on the date of the Qualified Initial Public Offering (“QIPO”). The Discount Rate will increase at increments of an additional two percent as of the first day of each successive six months period after June 2018 but shall in no event exceed twenty percent.
Additional percentage of distribution to preferred shareholders on liquidation							5.00%
Percentage of internal rate of return on preferred share redemption							15.00%
Series C Preferred Shares \| Maximum \| Scenario Forecast
Convertible Preferred Shares and Warrants [Line Items]
Preferred Stock Additional Dividend Rate Percentage	10.00%
Series C Preferred Shares \| Minimum [Member] \| Scenario Forecast
Convertible Preferred Shares and Warrants [Line Items]
Preferred Stock Additional Dividend Rate Percentage	1.00%
A1, A2, B1 and B2 Preferred Shares
Convertible Preferred Shares and Warrants [Line Items]
Preferred shares to ordinary shares conversion basis							one-for-one basis
Series B One And B Two Convertible Preferred Shares
Convertible Preferred Shares and Warrants [Line Items]
Additional percentage of distribution to preferred shareholders on liquidation							5.00%

Loss Per Share - Summary of Basic and Diluted Net Loss Per Share (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net loss attributable to ordinary shareholders	$ (50,384,176)	$ (37,512,212)	$ (18,021,737)
Denominator:
Weighted average number of ordinary shares- basic and diluted	21,752,757	9,439,028	8,693,655
Net loss per share-basic and diluted	$ (2.32)	$ (3.97)	$ (2.07)

Loss Per Share - Summary of Anti-Dilutive Shares Excluded from Calculation of Diluted Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Series A1 Convertible Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted loss per share		8,466,665	8,466,665
Series A2 Convertible Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted loss per share		8,442,221	8,442,221
Series B1 Convertible Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted loss per share		5,562,335
Series B2 Convertible Preferred Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted loss per share		3,973,096
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted loss per share	6,548,377	7,228,141	4,309,232
Non-Vested Restricted Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted loss per share	693,333	2,309,490	2,948,148
Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted loss per share		461,808	461,808

Related Party Transactions - Schedule of Major Related Party and Relationship (Details)	12 Months Ended
	Dec. 31, 2017
Quan Venture Fund I, L.P.
Related Party Transaction [Line Items]
Relationship with the Group	Significantly influenced by Samantha Du, founder, chairman and CEO of the Company
Qiagen (Suzhou) Translational Medicine Co., Ltd.
Related Party Transaction [Line Items]
Relationship with the Group	Significant influence held by Samantha Du’s immediate family

- Definition

A description of the related party transaction, including transactions to which no amounts or nominal amounts were ascribed and such other information deemed necessary to an understanding of the effects of the transactions on the financial statements. Examples of common related party transactions are, sales, purchases and transfers of realty and personal property, services received or furnished, loans and leases to and from top management and affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=77888428&loc=SL77919370-209981

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
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-Section 50
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 210
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-Name Accounting Standards Codification
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-Name Accounting Standards Codification
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+ Details

Related Party Transactions - Schedule of Transactions Between Related Party (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)
Research and development \| Qiagen (Suzhou) Translational Medicine Co., Ltd.
Related Party Transaction [Line Items]
Transactions between its related party	$ 96,656

Related Party Transactions - Additional Information (Details) - Quan Venture Fund I, L.P.	1 Months Ended
	Apr. 30, 2017 USD ($)
Related Party Transaction [Line Items]
Cash consideration for investment disposed	$ 500,000
Gain/loss recognized upon disposal	$ 0

Share-based Compensation - Share Options - Additional Information (Details) - USD ($)		1 Months Ended							12 Months Ended
	Mar. 05, 2015	Sep. 30, 2017	May 31, 2017	Dec. 31, 2016	Aug. 31, 2016	Mar. 31, 2016	Oct. 31, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 25, 2016	Mar. 09, 2016	Oct. 22, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized	4,140,945											7,369,767	7,369,767	7,369,767
Contractual term	10 years
Vesting period	5 years
Options granted									264,480	2,918,993	4,309,232
Exercise price of options									$ 8.76	$ 1.53	$ 0.60
Weighted-average grant-date fair value of options granted									$ 13.92	$ 6.94	$ 1.62
Management and employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contractual term		10 years	10 years		10 years	10 years	10 years	10 years
Vesting period		5 years			5 years	5 years	5 years	5 years
Options granted		101,584	158,313		1,760,368	1,157,793	3,438,783	870,449
Exercise price of options		$ 18.0	$ 3.0		$ 1.74	$ 1.2	$ 0.6	$ 0.6
Management and employees \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			4 years
Management and employees \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			5 years
Management and employees \| Vesting one year after the grant date and the remainder monthly basis thereafter
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage							20.00%	20.00%
Management and employees \| Vesting anniversary year after the grant date
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage		20.00%			20.00%	20.00%
Management and employees \| Vesting anniversary year after the grant date \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage			25.00%
Management and employees \| Vesting anniversary year after the grant date \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage			20.00%
Individual Advisors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contractual term			10 years	10 years	10 years
Vesting period			3 years	3 years	3 years
Options granted			4,583	416	416
Exercise price of options			$ 3.0	$ 1.74	$ 1.74
Individual Advisors \| Vesting anniversary year after the grant date
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage			33.33%	33.33%	33.33%
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage	20.00%
Compensation expense									$ 4,751,933	$ 3,524,733	$ 419,709
Unrecognized compensation expense related to unvested share options granted									$ 18,419,319
Recognized over a weighted-average period									3 years 18 days

Share-based Compensation - Schedule of Assumptions Used to Estimate Fair Values of Share Options Granted (Details) - $ / shares	1 Months Ended
	Sep. 30, 2017	May 31, 2017	Dec. 31, 2016	Aug. 31, 2016	Mar. 31, 2016	Oct. 31, 2015	Mar. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free rate of return	3.50%	3.20%	3.40%	2.50%	2.80%	3.10%	3.10%
Contractual life of option	10 years	10 years	10 years	10 years	10 years	10 years	10 years
Estimated volatility rate	70.00%	70.00%	70.00%	70.00%	70.00%	70.00%	70.00%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Fair value of underlying ordinary shares	$ 27.93	$ 9.60	$ 8.04	$ 8.04	$ 7.14	$ 1.92	$ 1.62

Share-based Compensation - Summary of Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options, Outstanding, Beginning Balance	7,228,141	4,309,232
Number of options, Granted	264,480	2,918,993	4,309,232
Number of options, Exercised	(100,834)
Number of options, Forfeited	(843,410)	(84)
Number of options, Outstanding, Ending Balance	6,548,377	7,228,141	4,309,232
Number of options, Vested and Exercisable as of December 31, 2017	2,307,319
Number of options, Vested or expected to vest as of December 31, 2017	6,548,377
Weighted average exercise price, Outstanding, Beginning Balance	$ 0.97	$ 0.60
Weighted average exercise price, Granted	8.76	1.53	$ 0.60
Weighted average exercise price, Exercised	0.65
Weighted average exercise price, Forfeited	1.11	1.74
Weighted average exercise price, Outstanding, Ending Balance	1.28	$ 0.97	$ 0.60
Weighted average exercise price, Vested and Exercisable as of December 31, 2017	0.80
Weighted average exercise price, Vested or expected to vest as of December 31, 2017	$ 1.28
Weighted average remaining contractual term, Outstanding	8 years 21 days	9 years	9 years 8 months 4 days
Weighted average remaining contractual term, Vested and Exercisable as of December 31, 2017	7 years 10 months 2 days
Weighted average remaining contractual term, Vested or expected to vest as of December 31, 2017	8 years 21 days
Aggregate intrinsic value, Outstanding	$ 130,668,851	$ 53,677,170	$ 18,874,438
Aggregate intrinsic value, Vested and Exercisable as of December 31, 2017	47,134,503
Aggregate intrinsic value, Vested or expected to vest as of December 31, 2017	$ 130,668,851

Share-based Compensation - Allocation of Compensation Expense Related to Option (Details) - Stock Options - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 4,751,933	$ 3,524,733	$ 419,709
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	2,215,282	1,472,993	124,871
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 2,536,651	$ 2,051,740	$ 294,838

Share-based Compensation - Red Kingdom - Additional Information (Details) - USD ($)				1 Months Ended		12 Months Ended
	Jun. 15, 2017	Dec. 15, 2015	Apr. 03, 2014	May 31, 2014	Apr. 30, 2014	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total consideration						$ 157,654,695
Shares vested						2,309,490
Red Kingdom
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Ordinary shares issued			8,083,333
Total consideration			$ 141,971
Shares vested						811,667
Red Kingdom \| Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share issued to secure services				6,459,167	350,000
Compensation expenses, deemed service period				5 years
Shares vested	811,667				1,038,333
Unrecognized share-based compensation		$ 1,152,600
Non-vested restricted shares repurchased	1,329,999
Red Kingdom \| Restricted Shares \| Each yearly anniversary from the date of the agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage				20.00%
Red Kingdom \| Restricted Shares \| Each the contractually agreed milestones within each year
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage					20.00%
Red Kingdom \| Senior Management and Certain Advisors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Ordinary shares issued			7,847,500
Red Kingdom \| CEO \| Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares vested		1,921,000

Share-based Compensation - Red Kingdom - Summary of Non-vested Restricted Share Activity (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Numbers of non-vested restricted shares, Beginning Balance \| shares	2,309,490
Numbers of non-vested restricted shares, Vested \| shares	(2,309,490)
Numbers of non-vested restricted shares, Ending Balance \| shares	693,333
Weighted average grant date fair value, Beginning Balance \| $ / shares	$ 1.31
Weighted average grant date fair value, Vested \| $ / shares	1.03
Weighted average grant date fair value, Ending Balance \| $ / shares	$ 2.57
Red Kingdom
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Numbers of non-vested restricted shares, Beginning Balance \| shares	2,784,999
Numbers of non-vested restricted shares, Vested \| shares	(811,667)
Numbers of non-vested restricted shares, Forfeited \| shares	(1,329,999)
Numbers of non-vested restricted shares, Transferred to the company \| shares	(643,333)
Weighted average grant date fair value, Beginning Balance \| $ / shares	$ 0.60
Weighted average grant date fair value, Vested \| $ / shares	0.60
Weighted average grant date fair value, Forfeited \| $ / shares	0.60
Weighted average grant date fair value, Transferred to the Company \| $ / shares	$ 0.60

Share-based Compensation - Non-vested Restricted Shares - Additional Information (Details)						12 Months Ended
	Sep. 20, 2017 shares	Aug. 25, 2016 Installment shares	Jul. 15, 2016 Installment shares	Aug. 10, 2015 Installment shares	Apr. 03, 2014 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Sep. 30, 2017 USD ($) shares	May 31, 2017 shares	Mar. 31, 2017 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-vested restricted shares						693,333	2,309,490
Non-Vested Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share issued to secure services					3,500,000
Compensation expenses, deemed service period					5 years
Shares granted		75,000	58,333	166,667
Restricted period of sale or transfer of shares				3 years
Share repurchase right termination period		3 years	3 years	3 years
Number of installments for repurchase right termination \| Installment		36	36	36
Description of repurchase right termination						The Repurchase Right terminates over the three years commencing August 10, 2015, July 15, 2016 and August 25, 2016 in 36 equal monthly instalments thereafter, or immediately prior to the consummation of an IPO of the Company.
Unrecognized share-based compensation \| $					$ 840,000	$ 1,517,160			$ 2,421,288
Compensation expense \| $						$ 5,179,173	$ 1,400,545	$ 2,281,695
Non-Vested Restricted Shares \| CEO
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-vested restricted shares										2,100,000	2,100,000
Non-Vested Restricted Shares \| Independent Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares granted	50,000
Non-Vested Restricted Shares \| Individual Advisors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-vested restricted shares									134,516
Non-Vested Restricted Shares \| Each yearly anniversary from the date of the agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage	33.33%				20.00%

Share-based Compensation - Summary of Non-vested Restricted Share Activity (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Numbers of non-vested restricted shares, Beginning Balance \| shares	2,309,490
Numbers of non-vested restricted shares, Granted \| shares	50,000
Numbers of non-vested restricted shares, Vested \| shares	(2,309,490)
Numbers of non-vested restricted shares, Transferred from Red Kingdom \| shares	643,333
Numbers of non-vested restricted shares, Ending Balance \| shares	693,333
Weighted average grant date fair value, Beginning Balance \| $ / shares	$ 1.31
Weighted average grant date fair value, Granted \| $ / shares	27.93
Weighted average grant date fair value, Vested \| $ / shares	1.03
Weighted average grant date fair value, Transferred from Red Kingdom \| $ / shares	0.60
Weighted average grant date fair value, Ending Balance \| $ / shares	$ 2.57

Share-based Compensation - Allocation of Compensation Expense Related to Restricted Shares (Details) - Non-Vested Restricted Shares - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 5,179,173	$ 1,400,545	$ 2,281,695
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	3,848,165	825,822	964,012
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 1,331,008	$ 574,723	$ 1,317,683

Accumulated Other Comprehensive Loss - Summary of Accumulated Other Comprehensive Loss (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ (51,551,749)	$ (18,369,903)	$ (2,950,677)
Balance	235,170,960	(51,551,749)	(18,369,903)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(698,532)	(103,620)	(4,727)
Other comprehensive loss	1,148,440	(594,912)	(98,893)
Balance	$ 449,908	$ (698,532)	$ (103,620)

Licenses and Collaborative Arrangement - Additional information (Details) ¥ in Millions, $ in Millions								1 Months Ended		12 Months Ended
	Dec. 19, 2017 USD ($)	Apr. 30, 2017	Oct. 31, 2016	Sep. 30, 2016	Nov. 30, 2015	Sep. 30, 2015	Jul. 31, 2015	Jan. 31, 2018 USD ($)	Mar. 31, 2015	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CNY (¥)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 CNY (¥)	Dec. 31, 2015 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments										$ 0.3
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments to be made upon achievement										400.8
BMS
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date									2015-03
Sanofi
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date							2015-07
Upfront payments														$ 0.5
License agreement, expiration period														10 years
UCB
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date						2015-09
Upfront payments												$ 0.8
License agreement, expiration period												10 years	10 years
Hanmi
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date					2015-11
Upfront payments												$ 1.0		$ 6.0
License agreement, expiration period												10 years	10 years	10 years
Tesaro
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date				2016-09
Upfront payments												$ 15.0
License agreement, expiration period												10 years	10 years
GSK China
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date			2016-10
Upfront payments												$ 0.7	¥ 4.5
Bater
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments										0.3	¥ 2.0
Paratek
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date		2017-04
Upfront payments										$ 7.5
License agreement, expiration period										11 years	11 years
Five Prime
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date	Dec. 19, 2017
Future milestone payments to be made upon achievement	$ 39.0
Five Prime \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of upfront fees								$ 5.0

Restricted Net Assets - Additional Information (Details) - PRC - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Restricted Net Assets [Line Items]
Minimum required percentage of statutory reserves	10.00%
Percentage of statutory reserves to respective registered capital	50.00%
Statutory reserves	$ 0	$ 0
Restricted amount by subsidiaries	$ 80,951,618	$ 39,215,714

Employee Defined Contribution Plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Employee benefits, expense	$ 579,094	$ 288,666	$ 79,878

Commitments and Contingencies - Additional Information (Details) ¥ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 CNY (¥)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 CNY (¥)
Loss Contingencies [Line Items]
Total operating leases expenses	$ 916,612	$ 285,742	$ 148,274
JING
Loss Contingencies [Line Items]
Capital commitment to underlying investment	3,900,000			¥ 26.3	$ 3,900,000	¥ 26.3
Unfunded capital contribution commitment	2,000,000			¥ 13.2
Property and Equipment
Loss Contingencies [Line Items]
Purchase obligation	$ 4,926,073

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Operating Lease Agreements (Details)	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 1,311,102
2019	1,302,945
2020	358,342
2021	53,692
Total lease commitment	$ 3,026,081

Subsequent Events - Additional Information (Details) - USD ($)					1 Months Ended						3 Months Ended	12 Months Ended
	Mar. 29, 2018	Mar. 02, 2018	Jan. 01, 2018	Mar. 05, 2015	Sep. 30, 2017	May 31, 2017	Aug. 31, 2016	Mar. 31, 2016	Oct. 31, 2015	Mar. 31, 2015	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 25, 2018
Subsequent Event [Line Items]
Options granted												264,480	2,918,993	4,309,232
Exercise price of options												$ 8.76	$ 1.53	$ 0.60
Contractual term				10 years
Vesting period				5 years
Management and employees
Subsequent Event [Line Items]
Options granted					101,584	158,313	1,760,368	1,157,793	3,438,783	870,449
Exercise price of options					$ 18.0	$ 3.0	$ 1.74	$ 1.2	$ 0.6	$ 0.6
Contractual term					10 years	10 years	10 years	10 years	10 years	10 years
Vesting period					5 years		5 years	5 years	5 years	5 years
Management and employees \| Minimum
Subsequent Event [Line Items]
Vesting period						4 years
Management and employees \| Maximum
Subsequent Event [Line Items]
Vesting period						5 years
Management and employees \| Vesting anniversary year after the grant date
Subsequent Event [Line Items]
Vesting percentage					20.00%		20.00%	20.00%
Management and employees \| Vesting anniversary year after the grant date \| Minimum
Subsequent Event [Line Items]
Vesting percentage						25.00%
Management and employees \| Vesting anniversary year after the grant date \| Maximum
Subsequent Event [Line Items]
Vesting percentage						20.00%
Subsequent Event \| Group and Hanmi
Subsequent Event [Line Items]
Paymet due from party	$ 0
Accrued payment obligation	$ 0
License and collaboration agreement termination date	Mar. 29, 2018
Subsequent Event \| Entasis Therapeutics Holdings Inc.
Subsequent Event [Line Items]
Non-refundable upfront fees obligated to pay															$ 5,000,000
Subsequent Event \| Each yearly anniversary from the date of the agreement \| Restricted Shares
Subsequent Event [Line Items]
Vesting percentage		20.00%
Subsequent Event \| Independent Directors \| Restricted Shares
Subsequent Event [Line Items]
Shares granted			37,500
Subsequent Event \| Certain Management \| Restricted Shares
Subsequent Event [Line Items]
Shares granted		100,000
Subsequent Event \| 2017 Plan \| Management and employees
Subsequent Event [Line Items]
Options granted											1,153,750
Contractual term											10 years
Vesting period											5 years
Subsequent Event \| 2017 Plan \| Management and employees \| Minimum
Subsequent Event [Line Items]
Exercise price of options											$ 20.74
Subsequent Event \| 2017 Plan \| Management and employees \| Maximum
Subsequent Event [Line Items]
Exercise price of options											$ 24.58
Subsequent Event \| 2017 Plan \| Management and employees \| Vesting anniversary year after the grant date
Subsequent Event [Line Items]
Vesting percentage											20.00%

Financial Statements Schedule I - Condensed Balance Sheets (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 229,660,148	$ 83,948,770	$ 13,160,696	$ 7,152,274
Prepayments and other current assets	954,506	143,527
Total current assets	230,614,654	84,092,297
Total assets	249,634,228	88,907,285
Current liabilities:
Warrant liabilities		3,900,000
Other payables	3,101,459	750,118
Total current liabilities	12,069,144	5,173,456
Deferred income	2,394,124	778,434
Total liabilities	14,463,268	5,951,890
Mezzanine equity
Total mezzanine equity		134,507,144
Shareholders' (deficit) equity
Ordinary shares (par value of US$0.00006 per share; 83,333,333 shares authorized, 9,657,175 and 49,912,570 shares outstanding as of December 31, 2016 and 2017, respectively)	2,995	579
Subscription receivable	(18)	(5)
Additional paid-in capital	345,269,688	9,313,646
Accumulated deficit	(110,551,613)	(60,167,437)
Additional other comprehensive (loss) income	449,908	(698,532)
Total shareholders' (deficit) equity	235,170,960	(51,551,749)	(18,369,903)	(2,950,677)
Total liabilities, mezzanine equity and shareholders' (deficit) equity	249,634,228	88,907,285
Series A1 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		10,028,572
Series A2 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		18,278,572
Series B1 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		53,100,000
Series B2 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		53,100,000
Parent Company
Current assets:
Cash and cash equivalents	181,910,618	24,813,050	$ 3,114,070	$ 6,335,498
Prepayments and other current assets	450,333
Total current assets	182,360,951	24,813,050
Investment in subsidiaries	54,885,326	62,042,345
Total assets	237,246,277	86,855,395
Current liabilities:
Warrant liabilities		3,900,000
Other payables	593,317
Total current liabilities	593,317	3,900,000
Deferred income	1,482,000
Total liabilities	2,075,317	3,900,000
Mezzanine equity
Total mezzanine equity		134,507,144
Shareholders' (deficit) equity
Ordinary shares (par value of US$0.00006 per share; 83,333,333 shares authorized, 9,657,175 and 49,912,570 shares outstanding as of December 31, 2016 and 2017, respectively)	2,995	579
Subscription receivable	(18)	(5)
Additional paid-in capital	345,269,688	9,313,646
Accumulated deficit	(110,551,613)	(60,167,437)
Additional other comprehensive (loss) income	449,908	(698,532)
Total shareholders' (deficit) equity	235,170,960	(51,551,749)
Total liabilities, mezzanine equity and shareholders' (deficit) equity	$ 237,246,277	86,855,395
Parent Company \| Series A1 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		10,028,572
Parent Company \| Series A2 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		18,278,572
Parent Company \| Series B1 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		53,100,000
Parent Company \| Series B2 Convertible Preferred Shares
Mezzanine equity
Total mezzanine equity		$ 53,100,000

Financial Statements Schedule I - Condensed Balance Sheets (Parenthetical) (Details) - $ / shares	Dec. 31, 2017	Dec. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Apr. 30, 2015	Aug. 31, 2014
Condensed Balance Sheet Statements Captions [Line Items]
Ordinary shares, par value	$ 0.00006	$ 0.00006
Ordinary shares, shares authorized	83,333,333	83,333,333
Ordinary shares, shares outstanding	49,912,570	9,657,175
Series A1 Convertible Preferred Shares
Condensed Balance Sheet Statements Captions [Line Items]
Convertible preferred shares, par value		$ 0.00006				$ 0.00006
Convertible preferred shares, shares authorized		8,466,667
Convertible preferred shares, shares issued		8,466,665				6,244,443
Convertible preferred shares, shares outstanding		8,466,665
Series A2 Convertible Preferred Shares
Condensed Balance Sheet Statements Captions [Line Items]
Convertible preferred shares, par value		$ 0.00006			$ 0.00006
Convertible preferred shares, shares authorized		8,904,032
Convertible preferred shares, shares issued		8,442,221			8,442,221
Convertible preferred shares, shares outstanding		8,442,221
Series B1 Convertible Preferred Shares
Condensed Balance Sheet Statements Captions [Line Items]
Convertible preferred shares, par value		$ 0.00006		$ 0.00006
Convertible preferred shares, shares authorized		5,562,337
Convertible preferred shares, shares issued		5,562,335		5,562,335
Convertible preferred shares, shares outstanding		5,562,335
Series B2 Convertible Preferred Shares
Condensed Balance Sheet Statements Captions [Line Items]
Convertible preferred shares, par value		$ 0.00006	$ 0.00006
Convertible preferred shares, shares authorized		3,973,098
Convertible preferred shares, shares issued		3,973,096	3,973,096
Convertible preferred shares, shares outstanding		3,973,096
Parent Company
Condensed Balance Sheet Statements Captions [Line Items]
Ordinary shares, par value	$ 0.00006	$ 0.00006
Ordinary shares, shares authorized	83,333,333	83,333,333
Ordinary shares, shares outstanding	49,912,570	9,657,175
Parent Company \| Series A1 Convertible Preferred Shares
Condensed Balance Sheet Statements Captions [Line Items]
Convertible preferred shares, par value		$ 0.00006
Convertible preferred shares, shares authorized		8,466,667
Convertible preferred shares, shares issued		8,466,665
Convertible preferred shares, shares outstanding		8,466,665
Parent Company \| Series A2 Convertible Preferred Shares
Condensed Balance Sheet Statements Captions [Line Items]
Convertible preferred shares, par value		$ 0.00006
Convertible preferred shares, shares authorized		8,904,032
Convertible preferred shares, shares issued		8,442,221
Convertible preferred shares, shares outstanding		8,442,221
Parent Company \| Series B1 Convertible Preferred Shares
Condensed Balance Sheet Statements Captions [Line Items]
Convertible preferred shares, par value		$ 0.00006
Convertible preferred shares, shares authorized		5,562,337
Convertible preferred shares, shares issued		5,562,335
Convertible preferred shares, shares outstanding		5,562,335
Parent Company \| Series B2 Convertible Preferred Shares
Condensed Balance Sheet Statements Captions [Line Items]
Convertible preferred shares, par value		$ 0.00006
Convertible preferred shares, shares authorized		3,973,098
Convertible preferred shares, shares issued		3,973,096
Convertible preferred shares, shares outstanding		3,973,096

Financial Statements Schedule I - Condensed Statements of Operations and Comprehensive Loss (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
General and administrative	$ (12,049,518)	$ (6,380,144)	$ (2,762,292)
Loss from operations	(51,391,036)	(38,529,301)	(16,349,437)
Interest income	527,351	403,266	5,005
Changes in fair value of warrants	200,000	(1,920,000)	(1,980,000)
Equity in loss of subsidiaries	(249,652)
Other income	933,158	2,533,966	341,112
Loss before income tax	(50,384,176)	(37,512,212)	(18,021,737)
Income tax expense	0
Net loss attributable to ordinary shareholders	(50,384,176)	(37,512,212)	(18,021,737)
Net loss	(50,384,176)	(37,512,212)	(18,021,737)
Foreign currency translation adjustments	1,148,440	(594,912)	(98,893)
Comprehensive loss	(49,235,736)	(38,107,124)	(18,120,630)
Parent Company
Operating expenses:
General and administrative	(4,114,144)	(534,660)	(56,806)
Loss from operations	(4,114,144)	(534,660)	(56,806)
Interest income	50,060
Changes in fair value of warrants	200,000	(1,920,000)	(1,980,000)
Equity in loss of subsidiaries	(46,598,092)	(35,057,552)	(15,984,931)
Other income	78,000
Loss before income tax	(50,384,176)	(37,512,212)	(18,021,737)
Net loss attributable to ordinary shareholders	(50,384,176)	(37,512,212)	(18,021,737)
Net loss	(50,384,176)	(37,512,212)	(18,021,737)
Foreign currency translation adjustments	1,148,440	(594,912)	(98,893)
Comprehensive loss	$ (49,235,736)	$ (38,107,124)	$ (18,120,630)

Financial Statements Schedule I - Condensed Statements of Cash Flows (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from Operating activities:
Net loss	$ (50,384,176)	$ (37,512,212)	$ (18,021,737)
Adjustments to reconcile net loss to net cash provided by operating activities:
Share-based compensation	9,931,106	4,925,278	2,701,404
Change in fair value of warrants	(200,000)	1,920,000	1,980,000
Share of loss from equity method investment	249,652
Changes in operating assets and liabilities:
Prepayments and other current assets	(810,979)	(74,507)	33,713
Other payables	1,950,152	242,187	327,500
Deferred income	1,615,690	716,835	61,599
Net cash used in operating activities	(32,367,181)	(32,158,031)	(11,464,910)
Cash flows from investing activities:
Net cash used in investing activities	(10,434,231)	(2,729,497)	(738,470)
Cash flows from financing activities:
Proceed from issuance of convertible preferred shares, net of issuance cost	29,100,000	106,200,000	18,278,572
Proceeds from exercise of warrants	1,000,000
Proceeds from exercises of stock options	65,500
Proceeds from issuance of ordinary shares upon initial public offering	160,424,994
Payment of initial public offering costs	(2,730,299)
Net cash provided by financing activities	187,860,195	106,200,000	18,278,572
Effect of foreign exchange rate changes on cash and cash equivalents	652,595	(524,398)	(66,770)
Net increases in cash and cash equivalents	145,711,378	70,788,074	6,008,422
Cash and cash equivalents - beginning of the year	83,948,770	13,160,696	7,152,274
Cash and cash equivalents - end of the year	229,660,148	83,948,770	13,160,696
Parent Company
Cash flows from Operating activities:
Net loss	(50,384,176)	(37,512,212)	(18,021,737)
Adjustments to reconcile net loss to net cash provided by operating activities:
Share-based compensation	3,346,039	534,660	56,806
Change in fair value of warrants	(200,000)	1,920,000	1,980,000
Share of loss from equity method investment	46,598,092	35,057,552	15,984,931
Changes in operating assets and liabilities:
Prepayments and other current assets	(450,333)
Other payables	553,317
Deferred income	1,482,000
Net cash used in operating activities	944,939
Cash flows from investing activities:
Investment in subsidiaries	(31,707,566)	(84,501,020)	(21,500,000)
Net cash used in investing activities	(31,707,566)	(84,501,020)	(21,500,000)
Cash flows from financing activities:
Proceed from issuance of convertible preferred shares, net of issuance cost	29,100,000	106,200,000	18,278,572
Proceeds from exercise of warrants	1,000,000
Proceeds from exercises of stock options	65,500
Proceeds from issuance of ordinary shares upon initial public offering	160,424,994
Payment of initial public offering costs	(2,730,299)
Net cash provided by financing activities	187,860,195	106,200,000	18,278,572
Net increases in cash and cash equivalents	157,097,568	21,698,980	(3,221,428)
Cash and cash equivalents - beginning of the year	24,813,050	3,114,070	6,335,498
Cash and cash equivalents - end of the year	$ 181,910,618	$ 24,813,050	$ 3,114,070

Financial Statements Schedule I - Additional Information (Details)	Dec. 31, 2017
Condensed Financial Information Of Parent Company Only Disclosure [Abstract]
Percentage of restricted net assets of subsidiary exceeding consolidated net assets	25.00%