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Document and Entity Information	12 Months Ended
Document and Entity Information	Dec. 31, 2018 shares
Document And Entity Information [Abstract]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	ZLAB
Entity Registrant Name	Zai Lab Ltd
Entity Central Index Key	0001704292
Entity Common Stock, Shares Outstanding	58,355,903
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false

Consolidated Balance Sheets - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 62,951,607	$ 229,660,148
Short-term investments	200,350,000
Accounts receivable	89,708
Inventories	3,822
Prepayments and other current assets	5,749,260	954,506
Total current assets	269,144,397	230,614,654
Investments in equity investees	3,149,855	1,650,348
Prepayments for equipment	275,853	126,411
Property and equipment, net	20,494,482	11,853,764
Intangible assets, net	321,566	20,089
Long term deposits	556,738	306,825
Value added tax recoverable	8,044,258	5,062,137
Total assets	301,987,149	249,634,228
Current liabilities:
Short-term borrowings	3,642,616
Accounts payable	37,432,035	8,967,685
Other payables	7,766,843	3,101,459
Total current liabilities	48,841,494	12,069,144
Deferred income	2,063,942	2,394,124
Total liabilities	50,905,436	14,463,268
Commitments and contingencies (Note 19)
Shareholders' equity
Ordinary shares (par value of US$0.00006 per share; 83,333,333 shares authorized, 49,912,570 and 58,006,967 shares issued and outstanding as of December 31,2017 and 2018, respectively)	3,481	2,995
Subscription receivable		(18)
Additional paid-in capital	498,043,011	345,269,688
Accumulated deficit	(249,626,508)	(110,551,613)
Accumulated other comprehensive income	2,661,729	449,908
Total shareholders' equity	251,081,713	235,170,960
Total liabilities and shareholders' equity	$ 301,987,149	$ 249,634,228

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Ordinary shares, par value	$ 0.00006	$ 0.00006
Ordinary shares, shares authorized	83,333,333	83,333,333
Ordinary shares, shares issued	58,006,967	49,912,570
Ordinary shares, shares outstanding	58,006,967	49,912,570

Consolidated Statements of Operations - USD ($)	12 Months Ended
Consolidated Statements of Operations - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 129,452
Cost of sales	(43,590)
Gross profit	85,862
Operating expenses:
Research and development	(120,278,023)	$ (39,341,518)	$ (32,149,157)
Selling, general and administrative	(21,575,921)	(12,049,518)	(6,380,144)
Loss from operations	(141,768,082)	(51,391,036)	(38,529,301)
Interest income	3,260,634	527,351	403,266
Interest expense	(39,672)
Changes in fair value of warrants		200,000	(1,920,000)
Other income	1,968,325	933,158	2,533,966
Other expense	(1,909,549)	(403,997)	(143)
Loss before income tax and share of loss from equity method investment	(138,488,344)	(50,134,524)	(37,512,212)
Income tax expense	0
Share of loss from equity method investment	(586,551)	(249,652)
Net loss	(139,074,895)	(50,384,176)	(37,512,212)
Net loss attributable to ordinary shareholders	$ (139,074,895)	$ (50,384,176)	$ (37,512,212)
Loss per share - basic and diluted	$ (2.64)	$ (2.32)	$ (3.97)
Weighted-average shares used in calculating net loss per ordinary share - basic and diluted	52,609,810	21,752,757	9,439,028

Consolidated Statements of Comprehensive Loss - USD ($)	12 Months Ended
Consolidated Statements of Comprehensive Loss - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (139,074,895)	$ (50,384,176)	$ (37,512,212)
Other comprehensive (loss) income, net of tax of nil:
Foreign currency translation adjustments	2,211,821	1,148,440	(594,912)
Comprehensive loss	$ (136,863,074)	$ (49,235,736)	$ (18,120,630)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statements of Comprehensive Loss (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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 (Income)
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
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/ follow-on public offering, net of issuance cost	157,654,695	$ 575	157,654,120
Issuance of ordinary shares upon initial public offering/ follow-on public offering, net of issuance cost, 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
Issuance of ordinary shares upon vesting of restricted shares		$ 20	(38)	$ 18
Issuance of ordinary shares upon vesting of restricted shares, Shares		338,332
Exercise of shares option	$ 195,711	$ 16	195,695
Exercise of shares option, Shares	256,065	256,065
Issuance of ordinary shares upon initial public offering/ follow-on public offering, net of issuance cost	$ 140,348,473	$ 450	140,348,023
Issuance of ordinary shares upon initial public offering/ follow-on public offering, net of issuance cost, Shares		7,500,000
Share-based compensation	12,229,643		12,229,643
Net loss	(139,074,895)				(139,074,895)
Foreign currency translation adjustments	2,211,821					2,211,821
Balance at Dec. 31, 2018	$ 251,081,713	$ 3,481	$ 498,043,011		$ (249,626,508)	$ 2,661,729
Balance, Shares at Dec. 31, 2018	58,006,967	58,006,967

Consolidated Statements of Shareholders' (deficit) Equity (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement Of Stockholders Equity [Abstract]
Share issuance cost upon initial/follow-on public offering	$ 651,527	$ 2,770,299

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (139,074,895)	$ (50,384,176)	$ (37,512,212)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation of property and equipment	1,634,377	545,705	198,224
Amortization of intangible assets	15,398	2,422	781
Amortization of deferred income	(312,000)	(78,000)
Share-based compensation	12,229,643	9,931,106	4,925,278
Share of loss from equity method investment	586,551	249,652
Loss on disposal of property and equipment	704	12,961
Change in fair value of warrants		(200,000)	1,920,000
Changes in operating assets and liabilities:
Accounts receivable	(89,708)
Inventories	(3,822)
Prepayments and other current assets	(4,794,754)	(810,979)	(74,507)
Long term deposits	(249,913)	(38,845)	(267,980)
Value added tax recoverable	(2,982,121)	(3,685,216)	(1,376,921)
Accounts payable	28,464,350	8,444,347	(929,716)
Other payables	7,056,350	1,950,152	242,187
Deferred income	(18,182)	1,693,690	716,835
Net cash used in operating activities	(97,538,022)	(32,367,181)	(32,158,031)
Cash flows from investing activities:
Purchases of short-term investments	(200,350,000)
Purchase of cost method investment			(500,000)
Disposal of cost method investment		500,000
Purchase of equity method investment	(2,086,058)	(1,900,000)
Purchase of property and equipment	(10,015,005)	(9,102,330)	(2,223,882)
Disposal of property and equipment		82,789
Purchase of intangible assets	(102,834)	(14,690)	(5,615)
Net cash used in investing activities	(212,553,897)	(10,434,231)	(2,729,497)
Cash flows from financing activities:
Proceed from short-term borrowings	3,642,616
Proceed from issuance of convertible preferred shares, net of issuance cost		29,100,000	106,200,000
Proceeds from exercise of warrants		1,000,000
Proceeds from exercises of stock options	195,711	65,500
Proceeds from issuance of ordinary shares upon public offerings	141,000,000	160,424,994
Payment of public offering costs	(691,527)	(2,730,299)
Net cash provided by financing activities	144,146,800	187,860,195	106,200,000
Effect of foreign exchange rate changes on cash and cash equivalents	(763,422)	652,595	(524,398)
Net increase (decrease) in cash and cash equivalents	(166,708,541)	145,711,378	70,788,074
Cash and cash equivalents - beginning of the year	229,660,148	83,948,770	13,160,696
Cash and cash equivalents - end of the year	62,951,607	229,660,148	$ 83,948,770
Supplemental disclosure on non-cash investing and financing activities:
Payables for purchase of property and equipment	1,708,663	413,657
Payables for intangible assets	225,158
Payables for public offering costs		40,000
Conversion of convertible preferred shares		163,607,144
Exercise of warrants		$ 3,700,000
Supplemental disclosure of cash flow information:
Interest expense paid	$ 35,799

Organization and Principal Activities

12 Months Ended

Dec. 31, 2018

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, 2018, 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
Zai Lab (US) LLC	U.S.	April 21, 2017	100%	Operating company for business development and R&D activities

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

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, revenue recognition, 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) Short-term investments

Short-term investments are time deposits with original maturities more than three months. Short-term investments are stated at cost, which approximates fair value. Interests are included in interest income.

(g) Accounts receivable

Accounts receivable are recorded at the amounts due from customers and net of allowances for doubtful accounts. An allowance for doubtful accounts is recorded when the collection of the full amount is no longer probable. In evaluating the collectability of accounts receivable, the Group considers many factors including aging of the receivable due, the customer's payment history, creditworthiness, financial conditions, and current economic trends. Credit losses of accounts receivable, which may be for all or part of a particular accounts receivable, shall be deducted from the allowance. The related accounts receivable balance shall be charged off in the period in which the accounts receivable are deemed uncollectible. Recoveries of accounts receivable previously charged written off shall be recorded when received. The Group regularly reviews the adequacy and appropriateness of any allowance for doubtful accounts. No allowance for doubtful accounts was recorded as of December 31, 2018.

(h) Inventories

Inventories are stated at the lower of cost or net realizable value, with cost determined on a weighted average basis. The Group periodically reviews the composition of inventory in order to identify obsolete, slow-moving or otherwise non-saleable items. The Group will record a write-down to its net realizable value in the period that the decline in value is first identified. No inventory provision was recorded as of December 31, 2018.

(i) 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, 2016, 2017 and 2018.

(j) Prepayments for equipment

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

(k) 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.

(l) Long term deposits

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

(m) 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.

(n) Intangible assets

Intangible assets mainly consist of externally purchased software which are amortized over one to five years on a straight-line basis. Amortization expenses for the years ended December 31, 2016, 2017 and 2018 were $781, $2,422 and $15,398, respectively. Amortization expenses of the Group's intangible assets are expected to be approximately $206,881, $41,584, $26,562, $24,940 and $21,599 for the years ended December 31, 2019, 2020, 2021, 2022, 2023 and thereafter, respectively.

(o) 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, 2016, 2017 and 2018, there was no impairment of the value of the Group's long-lived assets.

(p) 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, short-term investments, accounts receivable, prepayments and other current assets, short-term borrowings, accounts payable and other payables. As of December 31, 2017 and 2018, the carrying values of cash and cash equivalents, short-term investments, accounts receivable, prepayments and other current assets, short-term borrowings, accounts payable and other payable approximated their fair values due to the short-term maturity of these instruments.

(q) Revenue recognition

In May 2014, the Financial Accounting Standards Board (FASB) issued a comprehensive new standard which amends revenue recognition principles. In 2018, the Group adopted of ASC topic 606 ("ASC 606"), Revenue from Contracts with Customers, in recognition of revenue. Under ASC 606, the Group recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration expected to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Group determines are within the scope of ASC 606, the Group performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Group satisfies a performance obligation. The Group only applies the five-step model to contracts when it is probable that the Group will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. Once a contract is determined to be within the scope of ASC 606 at contract inception, the Group reviews the contract to determine which performance obligations it must deliver and which of these performance obligations are distinct. The Group recognizes as revenue the amount of the transaction price that is allocated to each performance obligation when that performance obligation is satisfied or as it is satisfied.

The Group's principal source of revenue is product sales. The contracts with customers generally contain a single performance obligation and the Group recognizes revenue from product sales when the Group has satisfied the performance obligation by transferring control of the product to the customers. Control of the product generally transfers to the customer upon delivery.

The timing between the recognition of revenue for product sales and the receipt of payment is not significant. Therefore the Group do not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between the transfer of the promised good to the customer and receipt of payment will be one year or less

For the year ended December 31, 2018, the Group's product revenues were generated from the sale of ZEJULA (niraparib) to customers, which are typically healthcare providers such as oncology centers. The Group utilizes a distributor in Hong Kong for warehousing services. Based on the nature of the arrangement, the Group has determined that it is a principal in the transaction since the Group is primarily responsible for fulfilling the promise to provide the products to the customer, maintains inventory risk until delivery to the customer and has latitude in establishing the price. Revenue was recognized at the amount to which the Group expected to be entitled in exchange for the sale of the products, which is the sales price agreed with the customers. Consideration paid to the distributor is recognized in operating expenses.

(r) 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 Group has acquired rights to develop and commercialize product candidates. Upfront payments that relate to the acquisition of a new drug compound, as well as pre-commercial milestone payments, are immediately expensed as acquired in-process research and development in the period in which they are incurred, provided that the new drug compound did not also include processes or activities that would constitute a “business” as defined under US GAAP, the drug has not achieved regulatory approval for marketing and, absent obtaining such approval, has no established alternative future use. Milestone payments made to third parties subsequent to regulatory approval would be capitalized as intangible assets and amortized over the estimated remaining useful life of the related product. 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.

(s) 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 $2,065,510, $855,158 and $1,332,419 were included in other income for the years ended December 31, 2016, 2017 and 2018, respectively. Grants received with government specified performance obligations are recognized when all the obligations have been fulfilled. If such obligations are not satisfied, the Group may be required to refund the subsidy. Cash grants of $912,124 and $893,942 were recorded in deferred income as of December 31, 2017 and 2018 respectively, which will be recognized when the government specified performance obligation is satisfied.

According to the ADR program agreement, the Group has the right to receive reimbursements for using DB's services, subject to the compliance by the Group with the terms of the Agreement. The Group performed a detailed assessment of the requirements and recognizes the reimbursements it is expected to be entitled to over the five-year contract term as other income. For the year ended December 31, 2017 and 2018, $78,000 and $312,000 were recorded in other income, respectively, and $1,482,000 and $1,170,000 were recorded in deferred income as of December 31, 2017 and 2018, respectively.

(t) 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.

(u) 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.

(v) 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 determined the fair value of the stock options granted to employees. Before 2018, the Group applied binomial option pricing model in determining the estimated fair value of the options granted to employees. In 2018, the Group changed to use the Black-Scholes option valuation model since the Group expected the Black-Scholes option valuation model provide a better estimate of fair value. A change in the valuation technique is a change in accounting estimate for the purposes of applying ASC 250, and shall be applied prospectively to new awards.

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.

(w) Income taxes

Income tax expense includes (a) deferred tax expense, which generally represents the net change in the deferred tax asset or liability balance during the year plus any change in valuation allowances; (b) current tax expense, which represents the amount of tax currently payable to or receivable from a taxing authority; and (c) non-current tax expense, which represents the increases and decreases in amounts related to uncertain tax positions from prior periods and not settled with cash or other tax attributes.

The Group recognizes deferred tax assets and liabilities for temporary differences between the financial statement and income tax bases of assets and liabilities, which 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.

(x) 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.

(y) 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.

(z) 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, 2016, 2017 and 2018:

	Year ended December 31,
	2016		2017		2018
	$		$		$
A		14,625,500	*		*
B	*			7,651,617	*
C	*			7,104,015	*
D	*		*			25,515,178
E	*		*			14,664,364

*	Represents less than 10% of research and development expenses for the years ended December 31, 2016, 2017 and 2018.

Concentration of credit risk

Financial instruments that are potentially subject to significant concentration of credit risk consist of cash and cash equivalents, short-term investments, and prepayments to suppliers. The carrying amounts of cash and cash equivalents and short-term investments represent the maximum amount of loss due to credit risk. As of December 31, 2017 and 2018, all of the Group’s cash and cash equivalents and short-term investments 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 prepayments to suppliers, the Group 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 RMB25,660,869 and RMB26,878,093, which were denominated in RMB, as of December 31, 2017 and 2018, respectively, representing 2% and 6% of the cash and cash equivalents as of December 31, 2017 and 2018, respectively.

(aa) 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.

(ab) Recent accounting pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize leases on balance sheet and disclose key information about leasing arrangements. The new standard establishes a right-of-use (ROU) model that requires a lessee to recognize a ROU asset and lease liability on the balance sheet for all leases with terms of longer than 12 months. Leases will be classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the income statement. The standard is effective on January 1, 2019, with early adoption permitted. The Group adopted the new standard on January 1, 2019 and used the effective date as the date of initial application. In July 2018, the FASB issued an update that provided an additional transition option that allows companies to continue applying the guidance under the lease standard in effect at that time in the comparative periods presented in the consolidated financial statements. Companies that elect this option would record a cumulative-effect adjustment to the opening balance of retained earnings on the date of adoption. The Group elected this optional transition method. As of December 31, 2018, the Group has $3.3 million of future minimum operating lease commitments that are not currently recognized on its consolidated balance sheets (see Note 19). 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 June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which intended to reduce cost and complexity and to improve financial reporting for nonemployee share-based payments. The ASU expands the scope of Topic 718, Compensation—Stock Compensation (which currently only includes share-based payments to employees) to include share-based payments issued to nonemployees for goods or services. Consequently, the accounting for share-based payments to nonemployees and employees will be substantially aligned. The ASU supersedes Subtopic 505-50, Equity—Equity-Based Payments to Non-Employees. The amendments in this ASU are effective for public companies for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. Early adoption is permitted, but no earlier than a company’s adoption date of Topic 606, Revenue from Contracts with Customers. As of December 31, 2018, there was $93,822 of total unrecognized compensation expense related to unvested non-employee options or restricted shares. The Group does not expect the requirements of ASU 2018-07 will have a material impact on the consolidated financial statements.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): The amendments in ASU 2018-13 eliminate the requirements to disclose the amount and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, valuation processes for Level 3 fair value measurements, and policy for timing of transfers between levels. ASU 2018-13 also provides clarification in the measurement uncertainty disclosure by explaining that the disclosure is to communicate information about the uncertainty in measurement as of the reporting date. In addition, ASU 2018-13 added the following requirements: changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period; and range and weighted average of significant unobservable inputs used in Level 3 fair value measurements. Finally, ASU 2018-13 updated language to further encourage entities to apply materiality when considering de minimis for disclosure requirements. The guidance will be applied retrospectively for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with the exception of amendments to changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used for Level 3 fair value measurements, and the narrative description of measurement uncertainty which will be applied prospectively. Early adoption is permitted. The Group does not expect the requirements of ASU 2018-13 will have a material impact on the consolidated financial statements.

In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606. This update clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer and precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. The update is effective in fiscal years beginning after December 15, 2019, and interim periods therein, and early adoption is permitted for entities that have adopted ASC 606. This guidance should be applied retrospectively to the date of initial application of Topic 606. The Group is currently evaluating the impact on its financial statements of adopting this guidance.

Cash and Cash Equivalents

12 Months Ended

Dec. 31, 2018

Cash And Cash Equivalents [Abstract]

Cash and Cash Equivalents

3.	Cash and cash equivalents

	As of December 31,
	2017		2018
	$		$
Cash at bank and in hand		204,008,828		36,778,028
Cash equivalents		25,651,320		26,173,579
		229,660,148		62,951,607
Denominated in:
US$		224,878,393		58,253,341
RMB (note (i))		3,927,163		3,916,262
Hong Kong dollar (”HK$"）		—		19,890
Australia dollar ("A$")		854,592		762,114
		229,660,148		62,951,607

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.

Short-term investment

12 Months Ended

Dec. 31, 2018

Short Term Investment [Abstract]

Short-term investment

4.	Short-term investment

Short-term investment primarily comprises of the time deposits with original maturities between three months and one year. For the year ended December 31, 2018, the Group recorded the interest income of $2.4 million from the short-term investments in the consolidated statements of operations.

Inventories

12 Months Ended

Dec. 31, 2018

Inventory Disclosure [Abstract]

Inventories

5.Inventories

The Group’s inventory balance of $3,822 as of December 31, 2018 is a finished drug product purchased from Tesaro Inc.(“Tesaro”) for distribution in Hong Kong.

Investments in Equity Investees

12 Months Ended

Dec. 31, 2018

Equity And Cost Method Investment [Abstract]

Investments in equity investees

6.	Investments 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 was RMB26.3 million (or $4.0 million) in cash, representing 20% of the equity interest of JING. RMB13.1 million (or $1.9 million) of which was paid by the Group in 2017, and the remainder RMB13.2 million (or $2.1 million) was paid in 2018. 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 and $586,551 for the year ended December 31, 2017 and 2018, respectively.

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 13).

Property and Equipment, net

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Property and Equipment, net

7.	Property and equipment, net

Property and equipment consist of the following:

	As of December 31,
	2017			2018
	$			$
Office equipment		273,339			384,088
Electronic equipment		160,772			599,495
Vehicle		81,360			77,460
Laboratory equipment		1,686,133			3,916,615
Manufacturing equipment		2,832,726			9,368,930
Leasehold improvements		3,227,150			4,607,975
Construction in progress		4,252,894			3,747,838
		12,514,374			22,702,401
Less: accumulated depreciation		(660,610	)		(2,207,919	)
Property and equipment, net		11,853,764			20,494,482

Depreciation expenses for the years ended December 31, 2016, 2017 and 2018 were $198,224, $545,705 and $1,634,377, respectively.

Income Tax

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income tax

8.	Income Tax

Cayman Islands (“Cayman”)

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 (“BVI”)

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 (“AUST”)

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.

U.S. (“US”)

Zai Lab (US) LLC. is incorporated in U.S. and is subject to U.S. federal corporate income tax at a rate of 21%. Zai Lab (US) LLC. is also subject to state income tax in Delaware. Zai Lab (US) LLC. has no taxable income for all periods presented, therefore, no provision for income taxes is required.

Hong Kong (“HK”)

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, 2016, 2017 and 2018, 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,
	2016		2017			2018
	$		$			$
Cayman		2,454,660		3,886,673			1,218,542
BVI		—		8,375			1,873
PRC		26,111,094		40,971,742			127,711,113
HK		8,010,908		6,240,462			7,777,758
US		—		—			2,350,761
AUST		935,550		(723,076	)		14,848
		37,512,212		50,384,176			139,074,895

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, 2016, 2017 and 2018 are as follows:

	Year ended December 31,
	2016			2017			2018
	$			$			$
Statutory income tax rate		25	%		25	%		25	%
Share-based compensations		(2.92	%)		(3.27	%)		(1.93	%)
Non-deductible expenses		(1.59	%)		(0.79	%)		(0.38	%)
Prior year tax filing adjustment		—			—			1.55	%
Effect of different tax rate of subsidiary operation in other jurisdictions		(3.33	%)		(3.06	%)		(0.76	%)
Changes in valuation allowance		(17.16	%)		(17.88	%)		(23.48	%)
Effective income tax rate		—			—			—

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

	Year ended December 31,
	2016			2017			2018
	$			$			$
Deferred tax assets:
Depreciation of property and equipment, net		3,892			5,964			14,827
Government grants		166,336			187,762			186,811
Net operating loss forwards		8,086,361			17,075,387			49,726,611
Less: valuation allowance		(8,256,589	)		(17,269,113	)		(49,928,249	)
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 2017 and 2018, 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, 2017 and 2018. Amounts of operating loss carry forwards were $34,716,071, $72,137,289 and $204,693,365 for the year ended December 31, 2016, 2017 and 2018, respectively, which are expected to expire from 2020 to 2028.

Movement of the valuation allowance is as follows:

	2017			2018
	$			$
Balance as of January 1,		(8,256,589	)		(17,269,113	)
Additions		(9,012,524	)		(32,659,136	)
Balance as of December 31,		(17,269,113	)		(49,928,249	)

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.

Short-term Borrowings

12 Months Ended

Dec. 31, 2018

Other Liabilities Current [Abstract]

Short-term Borrowings

9.	Short-term borrowings

On June 25, 2018, Zai Lab (Suzhou) Co. Ltd. entered into a three-year facility agreement for RMB25,000,000 (or $3,642,616) with a local commercial bank, and the outstanding borrowing under this agreement was RMB 20,000,000 (or $2,914,093) as of December 31, 2018, which will be due in 2019. The borrowing is guaranteed by Zai Lab (Shanghai) Co. Ltd., with an average interest rate of 4.785%. The agreement does not contain any financial covenants or restrictions.

On December 12, 2018, Zai Biopharmaceutical (Suzhou) Co. Ltd. entered into a three-year facility agreement for RMB40,000,000 (or $5,828,185) with a local commercial bank, the outstanding borrowing under this agreement was RMB 5,000,000 (or $728,523) as of December 31, 2018, which will be due in 2019. The borrowing is guaranteed by Zai Lab (Shanghai) Co., Ltd., with average interest rate of 4.785%. The agreement does not contain any financial covenants or restrictions.

Other Payables

12 Months Ended

Dec. 31, 2018

Other Liabilities Current [Abstract]

Other Payables

10.	Other payables

Other payables consist of followings:

	As of December 31,
	2017		2018
	$		$
Payroll		1,607,740		3,699,169
Professional service fee		714,764		1,564,070
Payables for purchase of property and equipment		413,657		1,708,663
Payables for purchase of intangible assets		—		225,158
Others		365,298		569,783
		3,101,459		7,766,843

Convertible Preferred Shares and Warrants

12 Months Ended

Dec. 31, 2018

Temporary Equity Disclosure [Abstract]

Convertible preferred shares and warrants

11.	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 had 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 were 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, 2016, the Company recognized a loss from the increase in fair value of the warrants of $1.9 million. 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, 2018

Earnings Per Share [Abstract]

Loss per share

12.	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,
	2016			2017			2018
Numerator:
Net loss attributable to ordinary shareholders		(37,512,212	)		(50,384,176	)		(139,074,895	)
Denominator:
Weighted average number of ordinary shares-basic and diluted		9,439,028			21,752,757			52,609,810
Net loss per share-basic and diluted		(3.97	)		(2.32	)		(2.64	)

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, 2016, 2017 and 2018, 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,
	2016		2017		2018
Number of Series A1 Shares outstanding		8,466,665		—		—
Number of Series A2 Shares outstanding		8,442,221		—		—
Number of Series B1 Shares outstanding		5,562,335		—		—
Number of Series B2 Shares outstanding		3,973,096		—		—
Share options		7,228,141		6,548,377		8,761,735
Non-vested restricted shares		2,309,490		693,333		1,112,001
Warrants		461,808		—		—

Related Party Transactions

12 Months Ended

Dec. 31, 2018

Related Party Transactions

13.	Related party transactions

The table below sets forth the major related party and the relationship with the Group as of December 31, 2018:

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

In 2018, the Group incurred $125,679 research and development expense with Qiagen (Suzhou) Translational Medicine Co., Ltd. for drug research and development services.

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, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-based compensation

14.	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”).

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 subsequent to the IPO would be granted under the 2017 Plan.

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 beginning on the anniversary date one year after the grant date.

In 2018, the Group granted 2,759,750 share options to certain management and employees of the Group at the exercise price ranging from $17.60 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 beginning on the anniversary date one year after the grant date.

Before 2018, 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 U.S. 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.

From 2018, the Group changed to use the Black-Scholes option valuation model going forward in determining the estimated fair value of the options granted, because the new technique or model is expected to produce a better estimate of fair value. The change in valuation technique is accounted for as a change in accounting estimate under ASC 250 and applied prospectively to new awards.

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

	March 2016			August 2016			December 2016			May 2017			September 2017			2018
Risk-free rate of return		2.8	%		2.5	%		3.4	%		3.2	%		3.5	%	2.7%-3.2%
Contractual life of option	10 years			10 years			10 years			10 years			10 years			10 years
Expected term	n/a			n/a			n/a			n/a			n/a			6.5 years
Estimated volatility rate		70	%		70	%		70	%		70	%		70	%		70	%
Expected dividend yield		0	%		0	%		0	%		0	%		0	%		0	%
Fair value of underlying ordinary shares		7.14			8.04			8.04			9.60			27.93		17.60-24.58

A summary of option activity under the Plan during the years ended December 31, 2016, 2017 and 2018 is presented below:

	Number of options			Weighted average exercise price		Weighted average remaining contractual term		Aggregate intrinsic value
				$		Years		$
Outstanding at January 1, 2016		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
Granted		2,759,750			21.15		—		—
Exercised		(256,065	)		0.76		—		—
Forfeited		(290,327	)		3.73		—		—
Outstanding at December 31, 2018		8,761,735			7.47		7.80		138,009,758
Vested and Exercisable as of December 31, 2018		3,321,376			1.01		6.93		73,775,871
Vested or expected to vest as of December 31, 2018		8,761,735			7.47		7.80		138,009,758

The weighted-average grant-date fair value of the options granted in 2016, 2017 and 2018 were $6.94, $13.92 and $14.03 per share, respectively. The Group recorded compensation expense related to the options of $3,524,733, $4,751,933 and $9,403,059 for the year ended December 31, 2016, 2017 and 2018, respectively, which were classified in the accompanying consolidated statements of operations as follows:

	Year ended December 31,
	2016		2017		2018
	$		$		$
Selling, general and administrative		1,472,993		2,215,282		4,428,266
Research and development		2,051,740		2,536,651		4,974,793
Total		3,524,733		4,751,933		9,403,059

As of December 31, 2018, there was $46,006,585 of total unrecognized compensation expense related to unvested share options granted. That cost is expected to be recognized over a weighted-average period of 2.80 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 and one of the advisors of the Group to secure their services, pursuant to which all of their 6,459,167 and 350,000 ordinary shares of the Red Kingdom respectively became subject to transfer restrictions (the “Restricted Shares” and the “Advisor Restricted Shares”). 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.

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 September 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.

In 2018, 62,500 ordinary shares were authorized for grant to the independent directors, respectively. The restricted shares shall vest and be released from the restrictions in full on the first 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.

In 2018, 694,500 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 from the date of the agreement. Upon termination of the certain management's service with the Group for any reason, any shares that are outstanding and not yet vested will be immediately be forfeited.

The Group measured the fair value of the non-vested restricted shares as of respective grant dates, and recognized the amount as compensation expense over the deemed service period using a graded vesting attribution model on a straight-line basis.

The following table summarized the Group’s non-vested restricted share activity in 2018:

	Numbers of non-vested restricted shares			Weighted average grant date fair value
				$
Non-vested as of January 1, 2018		693,333			2.57
Granted		757,000			20.73
Vested		(338,332	)		1.95
Non-vested as of December 31, 2018		1,112,001			15.13

As of December 31, 2018, there was $14,386,103 of total unrecognized compensation expense related to non-vested restricted shares. The Group recorded compensation expense related to the restricted shares of $1,400,545, $5,179,173 and $2,826,584 for the year ended December 31, 2016, 2017 and 2018, respectively, which were classified in the accompanying consolidated statements of operations as follows:

	Year ended December 31,
	2016		2017		2018
	$		$		$
Selling, general and administrative		825,822		3,848,165		2,206,046
Research and development		574,723		1,331,008		620,538
Total		1,400,545		5,179,173		2,826,584

Accumulated Other Comprehensive Loss

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Accumulated Other Comprehensive Loss

15.	Accumulated other comprehensive loss

The movement of accumulated other comprehensive loss is as follows:

	Foreign currency translation adjustments
	$
Balance as of January 1, 2016		(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
Other comprehensive income		2,211,821
Balance as of December 31, 2018		2,661,729

Licenses and Collaborative Arrangement

12 Months Ended

Dec. 31, 2018

Research And Development [Abstract]

Licenses and collaborative arrangement

16.	Licenses and collaborative arrangement

The following is a description of the Group’s significant collaboration agreements for the year ended December 31, 2016, 2017 and 2018.

License and collaboration agreement with 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.

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 made a milestone payment of $5.0 million to Paratek for the achievement of milestone upon receipt of the first regulatory approval for the Product in the U.S. in 2018. The Group will make further milestone payments to Paratek for the achievement of certain development milestone and sales milestone event. In addition, the Group 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 III 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 made an upfront payment of $5.0 million in January 2018, and made a milestone payment of $2.0 million to Five Prim for the achievement of a milestone by enrolling the first patient in Phase III FIGHT trail of the Product in China in October 2018. The Group will make further milestone payments 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. And the Group is also eligible to receive a royalty from Five Prime on net sales of FPA144 outside of Greater China.

License and collaboration agreement with Entasis Therapeutics Holdings Inc.(“Entasis”)

On April 25, 2018, the Group entered into an exclusive license agreement with 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 paid $5.0 million upfront fees to Entasis upon entering the agreement in 2018. And the Group will make future milestone payments upon the achievement of contractually specified development, regulatory and sales milestones, plus royalties.

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

License and collaboration agreement with Crescendo Biologics Ltd. (“Crescendo”)

On May 25, 2018, the Group and Crescendo entered into an exclusive, worldwide licensing agreement, under which the Group will develop, commercialize, and manufacture a topical, innovative antibody VH domain therapeutic for potential application in inflammatory indications.

Under the terms of the agreement, Crescendo granted to the group a worldwide exclusive license to develop and commercialize its drug candidate for all indications. The Group will be responsible for conducting all regulatory filings, clinical studies, and commercialization activities, with both companies participating in a Joint Development Committee.

The Group paid $2.0 million upfront fees to Crescendo in 2018. And the Group will provide development, regulatory, and commercial milestones for multiple indications. Crescendo will also be eligible to receive tiered royalties on global sales.

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

License and collaboration agreement with Novocure Limited (“Novocure”)

On September 10, 2018, the Group entered into an exclusive license agreement with Novocure for Tumor Treating Fields, including the brand name Optune in Greater China and a global strategic development collaboration.

Under the terms of agreement, Novocure granted the Group an exclusive license to commercialize Tumor Treating Fields in China, Hong Kong, Macau and Taiwan. The Group will be responsible for regulatory submissions in Greater China and will work to establish Tumor Treating Fields as an oncology treatment in this territory.

The Group paid $15.0 million upfront fees to Novocure in 2018 and will make future milestone payments upon the achievement of contractually certain development, regulatory and commercial milestones. Novocure will also be eligible to receive a royalty on net sales of the licensed products in Greater China.

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

License and collaboration agreement with MacroGenics Inc. (“MacroGenics”)

On November 29, 2018, the Group entered into an exclusive collaboration and license agreement with MarcroGenics to develop and commercialize Margetuximab, MGD013 and TRIDENT™ Molecule in Greater China.

Under the terms of agreement, MacroGenics granted the Group regional development and commercialization rights for these programs in mainland China, Hong Kong, Macau and Taiwan. The Group will lead clinical development in its territory by leveraging its regulatory and clinical development expertise and broad regional network of investigators. As part of the collaborative clinical development effort, the Group and MacroGenics intend to initiate a global study using combination regimens containing margetuximab in order to maximize potential clinical benefit in gastric cancer, the fifth most common cancer in the world and the second most common in China.

The Group paid upfront fee of $25.0 million to MacroGenics in January 2019, and will make future milestone payments upon the achievement of potential development and regulatory-based milestone payments. In addition, the Group would pay MacroGenics royalties on annual net sales of the assets, which may be subject to adjustment in specified circumstances.

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

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 and $7.0 million milestone payment under these agreements for the years ended December 31, 2017 and 2018, respectively. 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 $1,118.3 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, 2018

Restricted Net Assets [Abstract]

Restricted net assets

17.	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, 2017 and 2018, 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, 2017 and 2018, amounts restricted are the paid-in capital of the Group's PRC subsidiaries, which amounted to $80,951,618 and $90,951,618, respectively.

Employee Defined Contribution Plan

12 Months Ended

Dec. 31, 2018

Compensation And Retirement Disclosure [Abstract]

Employee defined contribution plan

18.	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 $288,666, $579,094 and $1,424,873 for the years ended December 31, 2016, 2017 and 2018, respectively.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

19.	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 $285,742, $916,612 and $1,494,456 for the years ended December 31, 2016, 2017 and 2018, respectively.

Future minimum lease payments under operating lease agreements at December 31, 2018 were as follows:

	Year ended December 31,
	$
2019		2,168,770
2020		1,007,476
2021		164,418
2022 and thereafter		—
Total lease commitment		3,340,664

(b)	Purchase commitments

As of December 31, 2018, the Group’s commitments related to purchase of property and equipment contracted but not yet reflected in the consolidated financial statement was $1,454,796 which is expected to be incurred within one year.

(c)	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 16).

Subsequent events

12 Months Ended

Dec. 31, 2018

Subsequent Events [Abstract]

Subsequent events

20.	Subsequent events

In January 2019, the Group terminated the license agreement with UCB Biopharma Sprl (“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, or ZL-1101 for the treatment, prevention and diagnosis of any human diseases. The license that the Group retained was reverted back to UCB immediately upon termination of the license agreement and the Group has no continuing obligations (financial or otherwise) thereunder.

In February 2019, the Group granted 5,000 share options to certain management and employees of the Group at the exercise price of $29.12per share under the 2017 Plan. 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 on the anniversary date one year after the grant date.

In March 2019, the Group granted 168,500 share options to certain management and employees of the Group at the exercise price of $27.75 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.

In January 2019, 50,000 ordinary shares were authorized for grant to the independent directors of the Group. The restricted shares shall vest and be released from the restrictions in full on the first anniversary from the date of the agreement.

In March 2019, 45,000 ordinary shares were authorized for grant to certain management and employees of the Group. One fifth of the restricted shares shall vest and be released from the restrictions on each yearly anniversary of the date of the agreement.

Financial Statements Schedule I

12 Months Ended

Dec. 31, 2018

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,
	2017			2018
	$			$
Assets
Current assets:
Cash and cash equivalents		181,910,618			745,980
Short-term investment		—			200,350,000
Prepayments and other current assets		450,333			2,912,408
Total current assets		182,360,951			204,008,388
Investment in subsidiaries		54,885,326			48,747,970
Total assets		237,246,277			252,756,358
Liabilities and shareholders' deficits
Liabilities
Current liabilities:
Other payables		593,317			504,645
Total current liabilities		593,317			504,645
Deferred income		1,482,000			1,170,000
Total liabilities		2,075,317			1,674,645
Shareholders' equity
Ordinary shares (par value of US$0.00006 per share; 83,333,333 shares authorized, 49,803,050 and 58,006,967 shares outstanding as of December 31, 2017 and 2018, respectively)		2,995			3,481
Subscription receivable		(18	)		—
Additional paid-in capital		345,269,688			498,043,011
Accumulated deficit		(110,551,613	)		(249,626,508	)
Additional other comprehensive income		449,908			2,661,729
Total shareholders' equity		235,170,960			251,081,713
Total liabilities and shareholders' equity		237,246,277			252,756,358

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,
	2016			2017			2018
	$			$			$
Operating Expenses:
Research and development		—			—			(234,185	)
General and administrative		(534,660	)		(4,114,144	)		(4,250,655	)
Loss from operations		(534,660	)		(4,114,144	)		(4,484,840	)
Interest income		—			50,060			3,041,842
Changes in fair value of warrants		(1,920,000	)		200,000			—
Equity in loss of subsidiaries		(35,057,552	)		(46,598,092	)		(137,943,897	)
Other income		—			78,000			312,000
Loss before income tax		(37,512,212	)		(50,384,176	)		(139,074,895	)
Income tax expense		—			—			—
Net loss attributable to ordinary shareholders		(37,512,212	)		(50,384,176	)		(139,074,895	)
Net loss		(37,512,212	)		(50,384,176	)		(139,074,895	)
Other comprehensive (loss) income, net of tax of nil:
Foreign currency translation adjustment		(594,912	)		1,148,440			2,211,821
Comprehensive loss		(38,107,124	)		(49,235,736	)		(136,863,074	)

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,
	2016			2017			2018
	$			$			$
Cash flows from Operating activities:
Net loss		(37,512,212	)		(50,384,176	)		(139,074,895	)
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of deferred income		—			(78,000	)		(312,000	)
Share based compensation		534,660			3,346,039			1,408,110
Change of fair value of warrants		1,920,000			(200,000	)		—
Equity in loss of subsidiaries		35,057,552			46,598,092			137,943,897
Changes in operating assets and liabilities:
Prepayments and other current assets		—			(450,333	)		(2,462,075	)
Other payables		—			553,317			(48,672	)
Deferred income		—			1,560,000			—
Net cash provided by operating activities		—			944,939			(2,545,635	)

Cash flows from investing activities:
Purchases of short-term investments		—			—			(200,350,000	)
Investment in subsidiaries		(84,501,020	)		(31,707,566	)		(118,773,187	)
Net cash used in investing activities		(84,501,020	)		(31,707,566	)		(319,123,187	)

Cash flows from financing activities:
Proceed from issuance of convertible preferred shares, net of issuance cost		106,200,000			29,100,000			—
Proceeds from exercise of warrants		—			1,000,000			—
Proceeds from exercises of stock options		—			65,500			195,711
Proceeds from issuance of ordinary shares upon public offerings		—			160,424,994			141,000,000
Payment of public offering costs		—			(2,730,299	)		(691,527	)
Net cash provided by financing activities		106,200,000			187,860,195			140,504,184

Effect of foreign exchange rate changes on cash and cash equivalent		—			—			—
Net increase (decrease) in cash and cash equivalents		21,698,980			157,097,568			(181,164,638	)
Cash and cash equivalents-beginning of the year		3,114,070			24,813,050			181,910,618
Cash and cash equivalents-end of the year		24,813,050			181,910,618			745,980

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, 2017 and 2018, there were no material contingencies, significant provisions of long term obligations, mandatory dividend or redemption requirements of redeemable stocks or guarantees of the Company.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

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

Short-term investments

(f) Short-term investments

Accounts receivable

(g) Accounts receivable

Inventories

(h) Inventories

Investments in equity investees

(i) Investments in equity investees

Prepayments for equipment

(j) 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

(k) 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

(l) Long term deposits

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

Value added tax recoverable

(m) Value added tax recoverable

Intangible assets

(n) Intangible assets

Impairment of long-lived assets

(o) Impairment of long-lived assets

Fair value measurements

(p) 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.

Revenue recognition

(q) Revenue recognition

Research and development expenses

(r) Research and development expenses

Deferred Income

(s) 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

(t) Leases

Comprehensive loss

(u) Comprehensive loss

Stock-based compensation

(v) 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

(w) Income taxes

Earnings (Loss) per share

(x) 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

(y) Segment information

Concentration of risks

(z) 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, 2016, 2017 and 2018:

	Year ended December 31,
	2016		2017		2018
	$		$		$
A		14,625,500	*		*
B	*			7,651,617	*
C	*			7,104,015	*
D	*		*			25,515,178
E	*		*			14,664,364

*	Represents less than 10% of research and development expenses for the years ended December 31, 2016, 2017 and 2018.

Concentration of credit risk

Foreign currency risk

Share consolidation (“reverse stock split”)

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

Recent accounting pronouncements

(ab) Recent accounting pronouncements

Organization and Principal Activities (Tables)

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Significant Operating Subsidiaries

As of December 31, 2018, 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
Zai Lab (US) LLC	U.S.	April 21, 2017	100%	Operating company for business development and R&D activities

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

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

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, 2016, 2017 and 2018:

	Year ended December 31,
	2016		2017		2018
	$		$		$
A		14,625,500	*		*
B	*			7,651,617	*
C	*			7,104,015	*
D	*		*			25,515,178
E	*		*			14,664,364

- 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, 2018

Cash And Cash Equivalents [Abstract]

Summary of Cash and Cash Equivalents

	As of December 31,
	2017		2018
	$		$
Cash at bank and in hand		204,008,828		36,778,028
Cash equivalents		25,651,320		26,173,579
		229,660,148		62,951,607
Denominated in:
US$		224,878,393		58,253,341
RMB (note (i))		3,927,163		3,916,262
Hong Kong dollar (”HK$"）		—		19,890
Australia dollar ("A$")		854,592		762,114
		229,660,148		62,951,607

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consist of the following:

	As of December 31,
	2017			2018
	$			$
Office equipment		273,339			384,088
Electronic equipment		160,772			599,495
Vehicle		81,360			77,460
Laboratory equipment		1,686,133			3,916,615
Manufacturing equipment		2,832,726			9,368,930
Leasehold improvements		3,227,150			4,607,975
Construction in progress		4,252,894			3,747,838
		12,514,374			22,702,401
Less: accumulated depreciation		(660,610	)		(2,207,919	)
Property and equipment, net		11,853,764			20,494,482

Income Tax (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Loss Before Income Taxes

Loss before income taxes consists of:

	Year ended December 31,
	2016		2017			2018
	$		$			$
Cayman		2,454,660		3,886,673			1,218,542
BVI		—		8,375			1,873
PRC		26,111,094		40,971,742			127,711,113
HK		8,010,908		6,240,462			7,777,758
US		—		—			2,350,761
AUST		935,550		(723,076	)		14,848
		37,512,212		50,384,176			139,074,895

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, 2016, 2017 and 2018 are as follows:

	Year ended December 31,
	2016			2017			2018
	$			$			$
Statutory income tax rate		25	%		25	%		25	%
Share-based compensations		(2.92	%)		(3.27	%)		(1.93	%)
Non-deductible expenses		(1.59	%)		(0.79	%)		(0.38	%)
Prior year tax filing adjustment		—			—			1.55	%
Effect of different tax rate of subsidiary operation in other jurisdictions		(3.33	%)		(3.06	%)		(0.76	%)
Changes in valuation allowance		(17.16	%)		(17.88	%)		(23.48	%)
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,
	2016			2017			2018
	$			$			$
Deferred tax assets:
Depreciation of property and equipment, net		3,892			5,964			14,827
Government grants		166,336			187,762			186,811
Net operating loss forwards		8,086,361			17,075,387			49,726,611
Less: valuation allowance		(8,256,589	)		(17,269,113	)		(49,928,249	)
Deferred tax assets, net		—			—			—

Schedule of Movement of Valuation Allowance

Movement of the valuation allowance is as follows:

	2017			2018
	$			$
Balance as of January 1,		(8,256,589	)		(17,269,113	)
Additions		(9,012,524	)		(32,659,136	)
Balance as of December 31,		(17,269,113	)		(49,928,249	)

Other Payables (Tables)

12 Months Ended

Dec. 31, 2018

Other Liabilities Current [Abstract]

Schedule of Other Payables

Other payables consist of followings:

	As of December 31,
	2017		2018
	$		$
Payroll		1,607,740		3,699,169
Professional service fee		714,764		1,564,070
Payables for purchase of property and equipment		413,657		1,708,663
Payables for purchase of intangible assets		—		225,158
Others		365,298		569,783
		3,101,459		7,766,843

Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2018

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,
	2016			2017			2018
Numerator:
Net loss attributable to ordinary shareholders		(37,512,212	)		(50,384,176	)		(139,074,895	)
Denominator:
Weighted average number of ordinary shares-basic and diluted		9,439,028			21,752,757			52,609,810
Net loss per share-basic and diluted		(3.97	)		(2.32	)		(2.64	)

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

	As of December 31,
	2016		2017		2018
Number of Series A1 Shares outstanding		8,466,665		—		—
Number of Series A2 Shares outstanding		8,442,221		—		—
Number of Series B1 Shares outstanding		5,562,335		—		—
Number of Series B2 Shares outstanding		3,973,096		—		—
Share options		7,228,141		6,548,377		8,761,735
Non-vested restricted shares		2,309,490		693,333		1,112,001
Warrants		461,808		—		—

Related Party Transactions (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018:

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

Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

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 2016			August 2016			December 2016			May 2017			September 2017			2018
Risk-free rate of return		2.8	%		2.5	%		3.4	%		3.2	%		3.5	%	2.7%-3.2%
Contractual life of option	10 years			10 years			10 years			10 years			10 years			10 years
Expected term	n/a			n/a			n/a			n/a			n/a			6.5 years
Estimated volatility rate		70	%		70	%		70	%		70	%		70	%		70	%
Expected dividend yield		0	%		0	%		0	%		0	%		0	%		0	%
Fair value of underlying ordinary shares		7.14			8.04			8.04			9.60			27.93		17.60-24.58

Summary of Option Activity

A summary of option activity under the Plan during the years ended December 31, 2016, 2017 and 2018 is presented below:

	Number of options			Weighted average exercise price		Weighted average remaining contractual term		Aggregate intrinsic value
				$		Years		$
Outstanding at January 1, 2016		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
Granted		2,759,750			21.15		—		—
Exercised		(256,065	)		0.76		—		—
Forfeited		(290,327	)		3.73		—		—
Outstanding at December 31, 2018		8,761,735			7.47		7.80		138,009,758
Vested and Exercisable as of December 31, 2018		3,321,376			1.01		6.93		73,775,871
Vested or expected to vest as of December 31, 2018		8,761,735			7.47		7.80		138,009,758

Allocation of Compensation Expense Related to Option

	Year ended December 31,
	2016		2017		2018
	$		$		$
Selling, general and administrative		1,472,993		2,215,282		4,428,266
Research and development		2,051,740		2,536,651		4,974,793
Total		3,524,733		4,751,933		9,403,059

Allocation of Compensation Expense Related to Restricted Shares

	Year ended December 31,
	2016		2017		2018
	$		$		$
Selling, general and administrative		825,822		3,848,165		2,206,046
Research and development		574,723		1,331,008		620,538
Total		1,400,545		5,179,173		2,826,584

Accumulated Other Comprehensive Loss (Tables)

12 Months Ended

Dec. 31, 2018

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, 2016		(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
Other comprehensive income		2,211,821
Balance as of December 31, 2018		2,661,729

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018 were as follows:

	Year ended December 31,
	$
2019		2,168,770
2020		1,007,476
2021		164,418
2022 and thereafter		—
Total lease commitment		3,340,664

Organization and Principal Activities - Schedule of Significant Operating Subsidiaries (Details)	12 Months Ended
	Dec. 31, 2018
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
Zai Lab (US) LLC
Subsidiary Of Limited Liability Company Or Limited Partnership [Line Items]
Place of incorporation	U.S.
Date of incorporation	Apr. 21, 2017
Percentage of ownership	100.00%
Principal activities	Operating company for business development and R&D activities

Summary of Significant Accounting Policies - Additional Information (Details)		12 Months Ended
	Aug. 30, 2017	Dec. 31, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 CNY (¥)	Dec. 31, 2017 CNY (¥)	Dec. 31, 2015 USD ($)
Significant Accounting Policies [Line Items]
Allowance for Doubtful Accounts Receivable		$ 0
Inventory provision		0
Impairment of investments		0	$ 0	$ 0
Amortization expenses		15,398	2,422	781
Finite-lived intangible assets, Amortization expense, 2019		206,881
Finite-lived intangible assets, Amortization expense, 2020		41,584
Finite-lived intangible assets, Amortization expense, 2021		26,562
Finite-lived intangible assets, Amortization expense, 2022		24,940
Finite-lived intangible assets, Amortization expense, 2023 and thereafter		21,599
Impairment of long-lived assets		0	0	0
Cash grants recorded in other income		1,332,419	855,158	2,065,510
Cash grants recorded in deferred income		$ 893,942	912,124
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		$ 62,951,607	$ 229,660,148	$ 83,948,770			$ 13,160,696
Share consolidation of ordinary shares and preferred shares	six-to-one
Unrecognized compensation expense related to unvested non-employee options or restricted shares		93,822
ASU 2016-02
Significant Accounting Policies [Line Items]
Unrecognized future minimum operating lease commitments		$ 3,300,000
Cash and Cash Equivalents
Significant Accounting Policies [Line Items]
Percentage of foreign currency risk		6.00%	2.00%
Foreign Currency Risk \| Cash and Cash Equivalents
Significant Accounting Policies [Line Items]
Aggregate amount of cash and cash equivalents \| ¥					¥ 26,878,093	¥ 25,660,869
Deferred Income
Significant Accounting Policies [Line Items]
Reimbursements recognized		$ 1,170,000	$ 1,482,000
Other Income
Significant Accounting Policies [Line Items]
Reimbursements recognized		$ 312,000	$ 78,000
Minimum
Significant Accounting Policies [Line Items]
Intangible assets amortization period		1 year
Maximum
Significant Accounting Policies [Line Items]
Intangible assets amortization period		5 years

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2018
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 - Suppliers Accounted for 10% or More of Research and Development Expenses (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Research and development expenses	$ 120,278,023	$ 39,341,518	$ 32,149,157
Research and Development Expenses \| Concentration of Suppliers \| A
Significant Accounting Policies [Line Items]
Research and development expenses			$ 14,625,500
Research and Development Expenses \| Concentration of Suppliers \| B
Significant Accounting Policies [Line Items]
Research and development expenses		7,651,617
Research and Development Expenses \| Concentration of Suppliers \| C
Significant Accounting Policies [Line Items]
Research and development expenses		$ 7,104,015
Research and Development Expenses \| Concentration of Suppliers \| D
Significant Accounting Policies [Line Items]
Research and development expenses	25,515,178
Research and Development Expenses \| Concentration of Suppliers \| E
Significant Accounting Policies [Line Items]
Research and development expenses	$ 14,664,364

Summary of Significant Accounting Policies - Suppliers Accounted for 10% or More of Research and Development Expenses (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash And Cash Equivalents [Line Items]
Cash at bank and in hand	$ 36,778,028	$ 204,008,828
Cash equivalents	26,173,579	25,651,320
Cash and cash equivalents	62,951,607	229,660,148	$ 83,948,770	$ 13,160,696
Denominated in US$
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	58,253,341	224,878,393
Denominated in RMB
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	3,916,262	3,927,163
Denominated in Hong Kong dollar
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	19,890
Denominated in Australia dollar
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	$ 762,114	$ 854,592

Short-term investment - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Maturities of Time Deposits, Description	the time deposits with original maturities between three months and one year
Time deposits, Interest income	$ 2.4
Minimum
Schedule Of Available For Sale Securities [Line Items]
Time deposits, Maturity period	3 months
Maximum
Schedule Of Available For Sale Securities [Line Items]
Time deposits, Maturity period	1 year

Inventories - Additional Information (Details)	Dec. 31, 2018 USD ($)
HK \| Tesaro
Inventory [Line Items]
Inventory, Finished Goods, Gross	$ 3,822

Investments in Equity Investees - Additional Information (Details) ¥ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 CNY (¥)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CNY (¥)	Jun. 30, 2017 USD ($) Investor	Jun. 30, 2017 CNY (¥) Investor	Oct. 31, 2016 USD ($)
Equity And Cost Method Investments [Line Items]
Capital contribution in cash		$ 2,086,058		$ 1,900,000
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		2,100,000	¥ 13.2	1,900,000	¥ 13.1
Capital contribution commitment						$ 4,000,000	¥ 26.3
Percentage of equity interest						20.00%	20.00%
Share of loss of investee		$ 586,551		$ 249,652

Property and Equipment, net - Schedule of Property and Equipment (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 22,702,401	$ 12,514,374
Less: accumulated depreciation	(2,207,919)	(660,610)
Property and equipment, net	20,494,482	11,853,764
Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	384,088	273,339
Electronic Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	599,495	160,772
Vehicle
Property Plant And Equipment [Line Items]
Property and equipment, gross	77,460	81,360
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,916,615	1,686,133
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	9,368,930	2,832,726
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,607,975	3,227,150
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,747,838	$ 4,252,894

Property and Equipment, net - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Depreciation expenses	$ 1,634,377	$ 545,705	$ 198,224

Income Tax - Additional Information (Details) - USD ($)	12 Months Ended
Income Tax - Additional Information (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Taxable income	$ (139,074,895)	$ (50,384,176)	$ (37,512,212)
Provision for income taxes	0
Amounts of operating loss carry forwards	$ 204,693,365	$ 72,137,289	$ 34,716,071
PRC
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%	25.00%	25.00%
Taxable income	$ (127,711,113)	$ (40,971,742)	$ (26,111,094)
Earliest Tax Year
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration	Dec. 31, 2020
Latest Tax Year
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration	Dec. 31, 2028
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 (US) LLC
Income Tax Disclosure [Line Items]
Statutory income tax rate	21.00%
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Loss before income taxes	$ 139,074,895	$ 50,384,176	$ 37,512,212
Cayman
Income Tax Disclosure [Line Items]
Loss before income taxes	1,218,542	3,886,673	2,454,660
BVI
Income Tax Disclosure [Line Items]
Loss before income taxes	1,873	8,375
PRC
Income Tax Disclosure [Line Items]
Loss before income taxes	127,711,113	40,971,742	26,111,094
HK
Income Tax Disclosure [Line Items]
Loss before income taxes	7,777,758	6,240,462	8,010,908
US
Income Tax Disclosure [Line Items]
Loss before income taxes	2,350,761
AUST
Income Tax Disclosure [Line Items]
Loss before income taxes	$ 14,848	$ (723,076)	$ 935,550

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Statutory income tax rate	25.00%	25.00%	25.00%
Share-based compensations	(1.93%)	(3.27%)	(2.92%)
Non-deductible expenses	(0.38%)	(0.79%)	(1.59%)
Prior year tax filing adjustment	1.55%
Effect of different tax rate of subsidiary operation in other jurisdictions	(0.76%)	(3.06%)	(3.33%)
Changes in valuation allowance	(23.48%)	(17.88%)	(17.16%)

Income Tax - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Depreciation of property and equipment, net	$ 14,827	$ 5,964	$ 3,892
Government grants	186,811	187,762	166,336
Net operating loss forwards	49,726,611	17,075,387	8,086,361
Less: valuation allowance	$ (49,928,249)	$ (17,269,113)	$ (8,256,589)

Income Tax - Schedule of Movement of Valuation Allowance (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Beginning Balance	$ (17,269,113)	$ (8,256,589)
Additions	(32,659,136)	(9,012,524)
Ending Balance	$ (49,928,249)	$ (17,269,113)

Short-term Borrowings - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 CNY (¥)	Dec. 12, 2018 USD ($)	Dec. 12, 2018 CNY (¥)	Jun. 25, 2018 USD ($)	Jun. 25, 2018 CNY (¥)
Zai Lab (Suzhou) Co., Ltd
Line Of Credit Facility [Line Items]
Facility agreement expiration period	3 years
Facility agreement amount					$ 3,642,616	¥ 25,000,000
Facility agreement, Outstanding amount	$ 2,914,093	¥ 20,000,000
Facility agreement, Expiration year	2019
Short-term borrowing, average interest rate	4.785%
Zai Biopharmaceutical (Suzhou) Co., Ltd
Line Of Credit Facility [Line Items]
Facility agreement expiration period	3 years
Facility agreement amount			$ 5,828,185	¥ 40,000,000
Facility agreement, Outstanding amount	$ 728,523	¥ 5,000,000
Facility agreement, Expiration year	2019
Short-term borrowing, average interest rate	4.785%

Other Payables - Schedule of Other Payables (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Other Liabilities Current [Abstract]
Payroll	$ 3,699,169	$ 1,607,740
Professional service fee	1,564,070	714,764
Payables for purchase of property and equipment	1,708,663	413,657
Payables for purchase of intangible assets	225,158
Others	569,783	365,298
Other payables, total	$ 7,766,843	$ 3,101,459

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, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) 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
Change in fair value of warrants \| $								(200,000)	1,920,000
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
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
Par value of issued convertible preferred shares						$ 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
Par value of issued convertible preferred shares					$ 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
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
Par value of issued convertible preferred shares				$ 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
Par value of issued convertible preferred shares			$ 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
Convertible Preferred Shares and Warrants [Line Items]
Preferred Stock Additional Dividend Rate Percentage	10.00%
Series C Preferred Shares \| Minimum
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss attributable to ordinary shareholders	$ (139,074,895)	$ (50,384,176)	$ (37,512,212)
Denominator:
Weighted average number of ordinary shares-basic and diluted	52,609,810	21,752,757	9,439,028
Net loss per share-basic and diluted	$ (2.64)	$ (2.32)	$ (3.97)

Loss Per Share - Summary of Anti-Dilutive Shares Excluded from Calculation of Diluted Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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
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
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	8,761,735	6,548,377	7,228,141
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	1,112,001	693,333	2,309,490
Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation of diluted loss per share			461,808

Related Party Transactions - Schedule of Major Related Party and Relationship (Details)	12 Months Ended
	Dec. 31, 2018
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 + Details

Related Party Transactions - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2017	Dec. 31, 2018
Quan Venture Fund I, L.P.
Related Party Transaction [Line Items]
Cash consideration for investment disposed	$ 500,000
Gain/loss recognized upon disposal	$ 0
Research and development \| Qiagen (Suzhou) Translational Medicine Co., Ltd.
Related Party Transaction [Line Items]
Transactions between its related party		$ 125,679

Share-based Compensation - Share Options - Additional Information (Details) - USD ($)	1 Months Ended					12 Months Ended
	Sep. 30, 2017	May 31, 2017	Dec. 31, 2016	Aug. 31, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 05, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized									4,140,945
Options granted						2,759,750	264,480	2,918,993
Exercise price of options						$ 21.15	$ 8.76	$ 1.53
Weighted-average grant-date fair value of options granted						$ 14.03	$ 13.92	$ 6.94
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense						$ 9,403,059	$ 4,751,933	$ 3,524,733
Unrecognized compensation expense related to unvested share options granted						$ 46,006,585
Recognized over a weighted-average period						2 years 9 months 18 days
Management and Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted		158,313		1,760,368	1,157,793
Exercise price of options		$ 3.0		$ 1.74	$ 1.2
Options granted contractual term		10 years		10 years	10 years
Vesting period				5 years	5 years
Management and Employees \| Two Thousand Seventeen Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted	101,584					2,759,750
Exercise price of options	$ 18.0
Options granted contractual term	10 years					10 years
Vesting period	5 years					5 years
Management and Employees \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		4 years
Management and Employees \| Minimum \| Two Thousand Seventeen Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of options						$ 17.60
Management and Employees \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		5 years
Management and Employees \| Maximum \| Two Thousand Seventeen Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of options						$ 24.58
Management and Employees \| Vesting anniversary year after the grant date
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting percentage				20.00%	20.00%
Management and Employees \| Vesting anniversary year after the grant date \| Two Thousand Seventeen Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting percentage	20.00%					20.00%
Management and Employees \| Vesting anniversary year after the grant date \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option 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]
Option vesting percentage		20.00%
Individual Advisors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted		4,583	416	416
Exercise price of options		$ 3.0	$ 1.74	$ 1.74
Options granted contractual term		10 years	10 years	10 years
Vesting period		3 years	3 years	3 years
Individual Advisors \| Vesting anniversary year after the grant date
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting percentage		33.33%	33.33%	33.33%

Share-based Compensation - Schedule of Assumptions Used to Estimate Fair Values of Share Options Granted (Details) - $ / shares	1 Months Ended
	Dec. 31, 2018	Sep. 30, 2017	May 31, 2017	Dec. 31, 2016	Aug. 31, 2016	Mar. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free rate of return		3.50%	3.20%	3.40%	2.50%	2.80%
Risk-free rate of return	2.70%
Risk-free rate of return	3.20%
Contractual life of option	10 years	10 years	10 years	10 years	10 years	10 years
Expected term	6 years 6 months
Estimated volatility rate	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%
Fair value of underlying ordinary shares		$ 27.93	$ 9.60	$ 8.04	$ 8.04	$ 7.14
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of underlying ordinary shares	$ 17.60
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of underlying ordinary shares	$ 24.58

Share-based Compensation - Summary of Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options, Outstanding, Beginning Balance	6,548,377	7,228,141	4,309,232
Number of options, Granted	2,759,750	264,480	2,918,993
Number of options, Exercised	(256,065)	(100,834)
Number of options, Forfeited	(290,327)	(843,410)	(84)
Number of options, Outstanding, Ending Balance	8,761,735	6,548,377	7,228,141	4,309,232
Number of options, Vested and Exercisable as of December 31, 2018	3,321,376
Number of options, Vested or expected to vest as of December 31, 2018	8,761,735
Weighted average exercise price, Outstanding, Beginning Balance	$ 1.28	$ 0.97	$ 0.60
Weighted average exercise price, Granted	21.15	8.76	1.53
Weighted average exercise price, Exercised	0.76	0.65
Weighted average exercise price, Forfeited	3.73	1.11	1.74
Weighted average exercise price, Outstanding, Ending Balance	7.47	$ 1.28	$ 0.97	$ 0.60
Weighted average exercise price, Vested and Exercisable as of December 31, 2018	1.01
Weighted average exercise price, Vested or expected to vest as of December 31, 2018	$ 7.47
Weighted average remaining contractual term, Outstanding	7 years 9 months 18 days	8 years 21 days	9 years	9 years 8 months 4 days
Weighted average remaining contractual term, Vested and Exercisable as of December 31, 2018	6 years 11 months 4 days
Weighted average remaining contractual term, Vested or expected to vest as of December 31, 2018	7 years 9 months 18 days
Aggregate intrinsic value, Outstanding	$ 138,009,758	$ 130,668,851	$ 53,677,170	$ 18,874,438
Aggregate intrinsic value, Vested and Exercisable as of December 31, 2018	73,775,871
Aggregate intrinsic value, Vested or expected to vest as of December 31, 2018	$ 138,009,758

Share-based Compensation - Allocation of Compensation Expense Related to Option (Details) - Stock Options - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 9,403,059	$ 4,751,933	$ 3,524,733
Selling, General and Administrative Expenses
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	4,428,266	2,215,282	1,472,993
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 4,974,793	$ 2,536,651	$ 2,051,740

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, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total consideration						$ 140,348,473	$ 157,654,695
Shares vested						338,332
Red Kingdom
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Ordinary shares issued			8,083,333
Total consideration			$ 141,971
Red Kingdom \| Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share issued to secure services				350,000	6,459,167
Shares vested	811,667				1,038,333
Unrecognized share-based compensation		$ 1,152,600
Non-vested restricted shares repurchased	1,329,999
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 - 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	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Sep. 30, 2017 USD ($) shares	May 31, 2017 shares	Mar. 31, 2017 shares	Apr. 03, 2014 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-vested restricted shares					1,112,001	693,333
Non-Vested Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
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 \| $					$ 14,386,103			$ 2,421,288			$ 840,000
Compensation expense \| $					$ 2,826,584	$ 5,179,173	$ 1,400,545
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				62,500
Non-Vested Restricted Shares \| Independent Directors \| Each yearly anniversary from the date of the agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting percentage	33.33%
Non-Vested Restricted Shares \| Management and Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares granted					694,500
Non-Vested Restricted Shares \| Management and Employees \| Each yearly anniversary from the date of the agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting percentage					20.00%
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

Share-based Compensation - Summary of Non-vested Restricted Share Activity (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Numbers of non-vested restricted shares, Beginning Balance \| shares	693,333
Numbers of non-vested restricted shares, Granted \| shares	757,000
Numbers of non-vested restricted shares, Vested \| shares	(338,332)
Numbers of non-vested restricted shares, Ending Balance \| shares	1,112,001
Weighted average grant date fair value, Beginning Balance \| $ / shares	$ 2.57
Weighted average grant date fair value, Granted \| $ / shares	20.73
Weighted average grant date fair value, Vested \| $ / shares	1.95
Weighted average grant date fair value, Ending Balance \| $ / shares	$ 15.13

Share-based Compensation - Allocation of Compensation Expense Related to Restricted Shares (Details) - Non-Vested Restricted Shares - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 2,826,584	$ 5,179,173	$ 1,400,545
Selling, General and Administrative Expenses
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	2,206,046	3,848,165	825,822
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation expense	$ 620,538	$ 1,331,008	$ 574,723

Accumulated Other Comprehensive Loss - Summary of Accumulated Other Comprehensive Loss (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ 235,170,960	$ (51,551,749)	$ (18,369,903)
Balance	251,081,713	235,170,960	(51,551,749)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	449,908	(698,532)	(103,620)
Other comprehensive income/loss	2,211,821	1,148,440	(594,912)
Balance	$ 2,661,729	$ 449,908	$ (698,532)

Licenses and Collaborative Arrangement - Additional information (Details) - USD ($) $ in Millions								1 Months Ended			12 Months Ended
	Nov. 29, 2018	Sep. 10, 2018	May 30, 2018	Apr. 25, 2018	Dec. 19, 2017	Apr. 30, 2017	Sep. 30, 2016	Jan. 31, 2019	Oct. 31, 2018	Jan. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments											$ 7.0	$ 0.3
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments to be made upon achievement												1,118.3
Tesaro
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date							2016-09
Upfront payments													$ 15.0
License agreement, expiration period													10 years
Paratek
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date						2017-04
Upfront payments												$ 7.5
License agreement, expiration period												11 years
Milestone payments											5.0
Five Prime
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments									$ 2.0
License agreement date					Dec. 19, 2017
Payment of upfront fees										$ 5.0
Entasis
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date				Apr. 25, 2018
Payment of upfront fees											5.0
Crescendo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date			May 25, 2018
Payment of upfront fees											2.0
Novocure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date		Sep. 10, 2018
Payment of upfront fees											$ 15.0
MacroGenics
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement date	Nov. 29, 2018
Payment of upfront fees								$ 25.0

Restricted Net Assets - Additional Information (Details) - PRC - USD ($)	Dec. 31, 2018	Dec. 31, 2017
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	$ 90,951,618	$ 80,951,618

Employee Defined Contribution Plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Employee benefits, expense	$ 1,424,873	$ 579,094	$ 288,666

Commitments and Contingencies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Total operating leases expenses	$ 1,494,456	$ 916,612	$ 285,742
Property and Equipment
Loss Contingencies [Line Items]
Purchase obligation	$ 1,454,796

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Operating Lease Agreements (Details)	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 2,168,770
2020	1,007,476
2021	164,418
Total lease commitment	$ 3,340,664

Subsequent Events - Additional Information (Details) - $ / shares	1 Months Ended							12 Months Ended
	Mar. 31, 2019	Feb. 28, 2019	Jan. 31, 2019	Sep. 30, 2017	May 31, 2017	Aug. 31, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Options granted								2,759,750	264,480	2,918,993
Exercise price of options								$ 21.15	$ 8.76	$ 1.53
Each yearly anniversary from the date of the agreement \| Restricted Shares
Subsequent Event [Line Items]
Vesting percentage	20.00%
Certain Management \| Restricted Shares
Subsequent Event [Line Items]
Shares granted	45,000
Management and Employees
Subsequent Event [Line Items]
Options granted					158,313	1,760,368	1,157,793
Exercise price of options					$ 3.0	$ 1.74	$ 1.2
Contractual term					10 years	10 years	10 years
Vesting period						5 years	5 years
Management and Employees \| Vesting anniversary year after the grant date
Subsequent Event [Line Items]
Vesting percentage						20.00%	20.00%
Two Thousand Seventeen Equity Incentive Plan \| Management and Employees
Subsequent Event [Line Items]
Options granted				101,584				2,759,750
Exercise price of options				$ 18.0
Contractual term				10 years				10 years
Vesting period				5 years				5 years
Two Thousand Seventeen Equity Incentive Plan \| Management and Employees \| Vesting anniversary year after the grant date
Subsequent Event [Line Items]
Vesting percentage				20.00%				20.00%
Subsequent Event \| Independent Directors \| Restricted Shares
Subsequent Event [Line Items]
Shares granted			50,000
Subsequent Event \| Two Thousand Seventeen Equity Incentive Plan \| Management and Employees
Subsequent Event [Line Items]
Options granted		5,000
Exercise price of options		$ 29.12
Contractual term		10 years
Vesting period		3 years
Subsequent Event \| Two Thousand Seventeen Equity Incentive Plan \| Management and Employees \| Vesting anniversary year after the grant date
Subsequent Event [Line Items]
Vesting percentage		33.33%
Scenario, Forecast \| Two Thousand Seventeen Equity Incentive Plan \| Management and Employees
Subsequent Event [Line Items]
Options granted	168,500
Exercise price of options	$ 27.75
Contractual term	10 years
Vesting period	5 years
Scenario, Forecast \| Two Thousand Seventeen Equity Incentive 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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 62,951,607	$ 229,660,148	$ 83,948,770	$ 13,160,696
Short-term investments	200,350,000
Prepayments and other current assets	5,749,260	954,506
Total current assets	269,144,397	230,614,654
Total assets	301,987,149	249,634,228
Current liabilities:
Other payables	7,766,843	3,101,459
Total current liabilities	48,841,494	12,069,144
Deferred income	2,063,942	2,394,124
Total liabilities	50,905,436	14,463,268
Shareholders' equity
Ordinary shares (par value of US$0.00006 per share; 83,333,333 shares authorized, 49,803,050 and 58,006,967 shares outstanding as of December 31, 2017 and 2018, respectively)	3,481	2,995
Subscription receivable		(18)
Additional paid-in capital	498,043,011	345,269,688
Accumulated deficit	(249,626,508)	(110,551,613)
Accumulated other comprehensive income	2,661,729	449,908
Total shareholders' equity	251,081,713	235,170,960	(51,551,749)	(18,369,903)
Total liabilities and shareholders' equity	301,987,149	249,634,228
Parent Company
Current assets:
Cash and cash equivalents	745,980	181,910,618	$ 24,813,050	$ 3,114,070
Short-term investments	200,350,000
Prepayments and other current assets	2,912,408	450,333
Total current assets	204,008,388	182,360,951
Investment in subsidiaries	48,747,970	54,885,326
Total assets	252,756,358	237,246,277
Current liabilities:
Other payables	504,645	593,317
Total current liabilities	504,645	593,317
Deferred income	1,170,000	1,482,000
Total liabilities	1,674,645	2,075,317
Shareholders' equity
Ordinary shares (par value of US$0.00006 per share; 83,333,333 shares authorized, 49,803,050 and 58,006,967 shares outstanding as of December 31, 2017 and 2018, respectively)	3,481	2,995
Subscription receivable		(18)
Additional paid-in capital	498,043,011	345,269,688
Accumulated deficit	(249,626,508)	(110,551,613)
Accumulated other comprehensive income	2,661,729	449,908
Total shareholders' equity	251,081,713	235,170,960
Total liabilities and shareholders' equity	$ 252,756,358	$ 237,246,277

Financial Statements Schedule I - Condensed Balance Sheets (Parenthetical) (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
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	58,006,967	49,912,570
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	58,006,967	49,803,050

Financial Statements Schedule I - Condensed Statements of Operations and Comprehensive Loss (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development expenses	$ 120,278,023	$ 39,341,518	$ 32,149,157
Loss from operations	(141,768,082)	(51,391,036)	(38,529,301)
Interest income	3,260,634	527,351	403,266
Changes in fair value of warrants		200,000	(1,920,000)
Equity in loss of subsidiaries	(586,551)	(249,652)
Other income	1,968,325	933,158	2,533,966
Loss before income tax	(139,074,895)	(50,384,176)	(37,512,212)
Income tax expense	0
Net loss attributable to ordinary shareholders	(139,074,895)	(50,384,176)	(37,512,212)
Net loss	(139,074,895)	(50,384,176)	(37,512,212)
Foreign currency translation adjustments	2,211,821	1,148,440	(594,912)
Comprehensive loss	(136,863,074)	(49,235,736)	(18,120,630)
Parent Company
Operating expenses:
Research and development expenses	234,185
General and administrative	(4,250,655)	(4,114,144)	(534,660)
Loss from operations	(4,484,840)	(4,114,144)	(534,660)
Interest income	3,041,842	50,060
Changes in fair value of warrants		200,000	(1,920,000)
Equity in loss of subsidiaries	(137,943,897)	(46,598,092)	(35,057,552)
Other income	312,000	78,000
Loss before income tax	(139,074,895)	(50,384,176)	(37,512,212)
Net loss attributable to ordinary shareholders	(139,074,895)	(50,384,176)	(37,512,212)
Net loss	(139,074,895)	(50,384,176)	(37,512,212)
Foreign currency translation adjustments	2,211,821	1,148,440	(594,912)
Comprehensive loss	$ (136,863,074)	$ (49,235,736)	$ (38,107,124)

Financial Statements Schedule I - Condensed Statements of Cash Flows (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from Operating activities:
Net loss	$ (139,074,895)	$ (50,384,176)	$ (37,512,212)
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of deferred income	(312,000)	(78,000)
Share-based compensation	12,229,643	9,931,106	4,925,278
Change in fair value of warrants		(200,000)	1,920,000
Share of loss from equity method investment	586,551	249,652
Changes in operating assets and liabilities:
Prepayments and other current assets	(4,794,754)	(810,979)	(74,507)
Other payables	7,056,350	1,950,152	242,187
Deferred income	(18,182)	1,693,690	716,835
Net cash used in operating activities	(97,538,022)	(32,367,181)	(32,158,031)
Cash flows from investing activities:
Purchases of short-term investments	(200,350,000)
Net cash used in investing activities	(212,553,897)	(10,434,231)	(2,729,497)
Cash flows from financing activities:
Proceed from issuance of convertible preferred shares, net of issuance cost		29,100,000	106,200,000
Proceeds from exercise of warrants		1,000,000
Proceeds from exercises of stock options	195,711	65,500
Proceeds from issuance of ordinary shares upon public offerings	141,000,000	160,424,994
Payment of public offering costs	(691,527)	(2,730,299)
Net cash provided by financing activities	144,146,800	187,860,195	106,200,000
Effect of foreign exchange rate changes on cash and cash equivalents	(763,422)	652,595	(524,398)
Net increase (decrease) in cash and cash equivalents	(166,708,541)	145,711,378	70,788,074
Cash and cash equivalents - beginning of the year	229,660,148	83,948,770	13,160,696
Cash and cash equivalents - end of the year	62,951,607	229,660,148	83,948,770
Parent Company
Cash flows from Operating activities:
Net loss	(139,074,895)	(50,384,176)	(37,512,212)
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of deferred income	(312,000)	(78,000)
Share-based compensation	1,408,110	3,346,039	534,660
Change in fair value of warrants		(200,000)	1,920,000
Share of loss from equity method investment	137,943,897	46,598,092	35,057,552
Changes in operating assets and liabilities:
Prepayments and other current assets	(2,462,075)	(450,333)
Other payables	(48,672)	553,317
Deferred income		1,560,000
Net cash used in operating activities	(2,545,635)	944,939
Cash flows from investing activities:
Purchases of short-term investments	(200,350,000)
Investment in subsidiaries	(118,773,187)	(31,707,566)	(84,501,020)
Net cash used in investing activities	(319,123,187)	(31,707,566)	(84,501,020)
Cash flows from financing activities:
Proceed from issuance of convertible preferred shares, net of issuance cost		29,100,000	106,200,000
Proceeds from exercise of warrants		1,000,000
Proceeds from exercises of stock options	195,711	65,500
Proceeds from issuance of ordinary shares upon public offerings	141,000,000	160,424,994
Payment of public offering costs	(691,527)	(2,730,299)
Net cash provided by financing activities	140,504,184	187,860,195	106,200,000
Net increase (decrease) in cash and cash equivalents	(181,164,638)	157,097,568	21,698,980
Cash and cash equivalents - beginning of the year	181,910,618	24,813,050	3,114,070
Cash and cash equivalents - end of the year	$ 745,980	$ 181,910,618	$ 24,813,050

Financial Statements Schedule I - Additional Information (Details)	Dec. 31, 2018
Condensed Financial Information Of Parent Company Only Disclosure [Abstract]
Percentage of restricted net assets of subsidiary exceeding consolidated net assets	25.00%