CRISPR Therapeutics (CRSP) 10-K 25 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2018	Feb. 21, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	CRSP
Entity Registrant Name	CRISPR THERAPEUTICS AG
Entity Central Index Key	1,674,416
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		52,279,167
Entity Public Float			$ 2.7

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash	$ 456,649	$ 239,758
Accounts receivable, including related party amounts of $88 and $821 as of December 31, 2018 and 2017, respectively	88	2,626
Prepaid expenses and other current assets, including related party amounts of $3,417 and $1,871 as of December 31, 2018 and 2017, respectively	9,658	6,001
Total current assets	466,395	248,385
Property and equipment, net	18,500	18,857
Intangible assets, net	289	344
Restricted cash	3,163	3,154
Other non-current assets	669	606
Total assets	489,016	271,346
Current liabilities:
Accounts payable	5,069	1,639
Accrued expenses, including related party amounts of $1,700 and $0 as of December 31, 2018 and 2017, respectively	20,852	11,361
Accrued tax liabilities	402	347
Deferred rent	1,202	1,027
Other current liabilities	221	137
Total current liabilities	27,746	14,511
Deferred revenue, including related party amounts of $57,780 and $91 as of December 31, 2018 and 2017, respectively	57,780	56,928
Deferred rent non-current	11,052	11,761
Other non-current liabilities	243	314
Total liabilities	96,821	83,514
Commitments and contingencies (Note 8)
Shareholders’ equity:
Common shares, CHF 0.03 par value, 52,183,139 and 41,092,969 shares authorized at December 31, 2018 and 2017, respectively, 52,160,798 and 41,037,121 shares issued at December 31, 2018 and 2017, respectively, 51,852,862, and 40,592,248 shares outstanding at December 31, 2018 and 2017, respectively, 20,498,996 and 17,338,291 shares in conditional capital at December 31, 2018 and 2017, respectively.	1,584	1,240
Treasury shares, at cost, 307,936 shares and 444,873 shares at December 31, 2018 and 2017, respectively	(57)	0
Additional paid-in capital	682,245	312,018
Accumulated deficit	(291,569)	(125,440)
Accumulated other comprehensive (loss) income	(8)	14
Total shareholders' equity	392,195	187,832
Total liabilities and shareholders’ equity	$ 489,016	$ 271,346

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) $ in Thousands	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares
Statement Of Financial Position [Abstract]
Accounts receivable, related party amount, current | $	$ 88	$ 821
Accrued expenses related party amount, current | $	1,700	0
Prepaid expenses and other current assets, related party amount | $	3,417	1,871
Deferred revenue non-current related party amount | $	$ 57,780	$ 91
Common stock, shares authorized	52,183,139	41,092,969
Common stock, shares issued	52,160,798	41,037,121
Common stock, shares outstanding	51,852,862	40,592,248
Common stock, conditional capital	20,498,996	17,338,291
Treasury stock, shares	307,936	444,873

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Collaboration revenue	[1]	$ 3,124	$ 40,997	$ 5,164
Operating expenses:
Research and development	[2]	113,773	69,800	42,238
General and administrative		48,294	35,845	31,056
Total operating expenses		162,067	105,645	73,294
Loss from operations		(158,943)	(64,648)	(68,130)
Other (expense) income:
Interest expense				(8,050)
Loss from equity method investment		(4,275)	(1,763)	(36,532)
Gain on extinguishment of convertible loan				11,482
Other (expense) income, net		(1,210)	(197)	78,512
Total other (expense) income, net		(5,485)	(1,960)	45,412
Net loss before provision for from income taxes		(164,428)	(66,608)	(22,718)
Provision for income taxes		(553)	(1,749)	(484)
Net loss		(164,981)	(68,357)	(23,202)
Foreign currency translation adjustment		(22)	40	(18)
Comprehensive loss		(165,003)	(68,317)	(23,220)
Reconciliation of net loss to net loss attributable to common shareholders:
Net loss		(164,981)	(68,357)	(23,202)
Loss attributable to noncontrolling interest				25
Net loss attributable to common shareholders		$ (164,981)	$ (68,357)	$ (23,177)
Net loss per share attributable to common shareholders—basic and diluted		$ (3.44)	$ (1.71)	$ (1.89)
Weighted-average common shares outstanding used in net loss per share attributable to common shareholders—basic and diluted		47,964,368	40,057,365	12,257,483
[1]	Including the following amounts of revenue from a related party, see Note 15:
[2]	Including the following amounts of research and development from a related party, see Note 15:

Consolidated Statements of Op_2

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue from related party	$ 3,124	$ 4,760	$ 1,190
Research and development expense with a related party	$ 23,982	$ 4,523	$ 1,755

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Shares and Shareholder's (Deficit) Equity - USD ($) $ in Thousands	Total	ViaCyte [Member]	Series A-1 Redeemable Convertible Preferred Shares [Member]	Series A-2 Redeemable Convertible Preferred Shares [Member]	Series A-3 Redeemable Convertible Preferred Shares [Member]	Series B Redeemable Convertible Preferred Shares [Member]	Common Shares [Member]	Common Shares [Member]ViaCyte [Member]	Common Shares [Member]TRACR Hematology Limited [Member]	Treasury Shares [Member]	Treasury Shares [Member]ViaCyte [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]ViaCyte [Member]	Additional Paid-in Capital [Member]TRACR Hematology Limited [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total CRISPR Therapeutics AG Shareholders' (Deficit) Equity [Member]	Total CRISPR Therapeutics AG Shareholders' (Deficit) Equity [Member]ViaCyte [Member]	Total CRISPR Therapeutics AG Shareholders' (Deficit) Equity [Member]TRACR Hematology Limited [Member]	Noncontrolling Interest [Member]	Noncontrolling Interest [Member]TRACR Hematology Limited [Member]
Beginning balance at Dec. 31, 2015			$ 1,169	$ 10,394	$ 22,518	$ 30,440
Beginning balance (in shares) at Dec. 31, 2015			440,001	3,120,001	10,758,006	4,519,016
Beginning balance at Dec. 31, 2015	$ (29,124)						$ 181					$ 4,636			$ (33,906)	$ (8)	$ (29,097)			$ (27)
Beginning balance (in shares) at Dec. 31, 2015							5,528,079
Conversion of Convertible Loans						$ 61,929
Conversion of Convertible Loans (in shares)						5,464,608
Receipt of preferred shares net of issuance cost and subscription receivable					$ 22,850
Issuance of preferred shares net of issuance cost and subscription receivable						$ 36,265
Issuance of preferred shares net of issuance cost and subscription receivable (in shares)						2,834,252
Conversion of redeemable convertible preferred shares into common share, value	185,565		$ (1,169)	$ (10,394)	$ (45,368)	$ (128,634)	$ 823					184,742					185,565
Conversion of redeemable convertible preferred shares into common share (in shares)			(440,001)	(3,120,001)	(10,758,006)	(12,817,876)	27,135,884
Adjustment to noncontrolling interest upon share exchange transaction									$ 10					$ (62)					$ (52)		$ 52
Adjustment to noncontrolling interest upon share exchange transaction (in shares)									328,017
Issuance of common stock, net of issuance costs	88,664						$ 213					88,451					88,664
Issuance of common stock, net of issuance costs (in shares)							7,100,000
Repurchase of treasury shares, value							$ (13)					13
Repurchase of treasury shares (in shares)							(444,873)			444,873
Vesting of restricted shares, value	82						$ 1					81					82
Vesting of restricted shares (in shares)							53,427
Exercise of vested options, value	35						$ 1					34					35
Exercise of vested options (in shares)							18,900
Stock- based compensation expense	10,844											10,844					10,844
Other comprehensive income (loss)	(18)															(18)	(18)
Net loss	(23,202)														(23,177)		(23,177)			$ (25)
Ending balance (in shares) at Dec. 31, 2016			0	0	0	0
Ending balance at Dec. 31, 2016	232,846						$ 1,216					288,739			(57,083)	(26)	232,846
Ending balance (in shares) at Dec. 31, 2016							39,719,434			444,873
Vesting of restricted shares, value	59						$ 1					58					59
Vesting of restricted shares (in shares)							33,519
Exercise of vested options, value	2,608						$ 23					2,585					2,608
Exercise of vested options (in shares)							839,295
Stock- based compensation expense	20,636											20,636					20,636
Other comprehensive income (loss)	40															40	40
Net loss	(68,357)														(68,357)		(68,357)
Ending balance (in shares) at Dec. 31, 2017			0	0	0	0
Ending balance at Dec. 31, 2017	187,832						$ 1,240					312,018			(125,440)	14	187,832
Ending balance (in shares) at Dec. 31, 2017							40,592,248			444,873
Cumulative effect of ASC 606 adoption | ASU 2014-09 [Member]	(1,148)														(1,148)		(1,148)
Issuance of common stock, net of issuance costs	307,053						$ 311					306,742					307,053
Issuance of common stock, net of issuance costs (in shares)							9,960,526
Repurchase of treasury shares, value	(57)									$ (57)							(57)
Repurchase of treasury shares (in shares)							(64,952)			64,952
Vesting of restricted shares, value	113						$ 1					112					113
Vesting of restricted shares (in shares)							38,761
Exercise of vested options, value	8,563						$ 26					8,537					8,563
Exercise of vested options (in shares)							946,131			(36,253)
Issuance of shares to ViaCyte		$ 15,582						$ 6					$ 15,576					$ 15,582
Issuance of shares to ViaCyte (in shares)								380,148			(165,636)
Stock- based compensation expense	39,260											39,260					39,260
Other comprehensive income (loss)	(22)															(22)	(22)
Net loss	(164,981)														(164,981)		(164,981)
Ending balance (in shares) at Dec. 31, 2018			0	0	0	0
Ending balance at Dec. 31, 2018	$ 392,195						$ 1,584			$ (57)		$ 682,245			$ (291,569)	$ (8)	$ 392,195
Ending balance (in shares) at Dec. 31, 2018							51,852,862			307,936

Consolidated Statements of Re_2

Consolidated Statements of Redeemable Convertible Preferred Shares and Shareholder's (Deficit) Equity (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2016USD ($)
Exercise of Vested Options [Member]
Issuance costs	$ 0.4
Common Shares [Member]
Issuance costs	$ 23.8	$ 8.3
Series B Redeemable Convertible Preferred Shares [Member]
Issuance costs		$ 1.8

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (164,981)	$ (68,357)	$ (23,202)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	3,519	3,024	925
Equity-based compensation	34,985	18,873	10,844
Non-cash interest			8,050
Unrealized foreign currency remeasurement (gain) loss		(9)	2
Gain on extinguishment of convertible loan			(11,482)
Other income - formation of joint venture			(78,608)
Loss from equity method investment	4,275	1,763	36,380
Non-cash expense related to ViaCyte transaction	15,582
Other income, non-cash	(169)
Changes in:
Accounts receivable	2,538	531	(2,818)
Prepaid expenses and other assets	(3,342)	(4,117)	(1,071)
Accounts payable and accrued expenses	12,110	(831)	3,860
Deferred revenue	(296)	(20,718)	1,917
Deferred rent	(709)	(522)	2,360
Other liabilities, net	249	270	(17)
Net cash used in operating activities	(96,239)	(70,093)	(52,860)
Investing activities
Purchase of property and equipment	(2,773)	(7,814)	(3,016)
Proceeds from contribution of intellectual property to equity method investee			35,000
Cash investment in equity method investee			(100)
Purchase of available for sale debt security		(500)
Net cash (used in) provided by investing activities	(2,773)	(8,314)	31,884
Financing activities
Proceeds from issuance of common shares, net of issuance costs	307,053	0	89,061
Proceeds from exercise of options	8,938	2,608	34
Repurchase of common shares	(57)
Issuance costs for preferred share financings			(1,810)
Proceeds from issuance of convertible loans			35,010
Net cash provided by financing activities	315,934	2,608	183,220
Effect of exchange rate changes on cash	(22)	41	(235)
Increase (decrease) in cash and restricted cash	216,900	(75,758)	162,009
Cash, cash equivalents and restricted cash, beginning of period	242,912	318,670	156,661
Cash, cash equivalents and restricted cash, end of period	459,812	242,912	318,670
Supplemental disclosure of non-cash investing and financing activities
Property and equipment purchases in accounts payable and accrued expenses	334		7,014
Stock option issuance costs included in accrued expenses	$ 375
Costs for proposed supplemental offering in accounts payable and accrued expenses		$ 290
Property and equipment related to lease incentives			10,785
Conversion of preferred shares to common shares upon IPO			185,565
Conversion of Vertex and Bayer convertible loans and accrued interest			61,929
Issuance costs for public offering in accounts payable and accrued expenses			397
Contribution of intellectual property to Casebia			36,380
Series A-3 Redeemable Convertible Preferred Shares [Member]
Financing activities
Proceeds from issuance of preferred shares			22,850
Series B Redeemable Convertible Preferred Shares [Member]
Financing activities
Proceeds from issuance of preferred shares			$ 38,075

Organization and Operations

Organization and Operations	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Operations	1. Organization and Operations Nature of business CRISPR Therapeutics AG (“CRISPR” or the “Company”) was formed on October 28, 2013 in Basel, Switzerland. The Company was established to translate CRISPR/Cas9, a genome editing technology, into transformative gene-based medicines for the treatment of serious human diseases. The foundational intellectual property underlying the Company’s operations was licensed to the Company and its subsidiaries in April 2014. The Company devotes substantially all of its efforts to product research and development activities, initial market development and raising capital. The Company’s principal offices are in Zug, Switzerland and operations are in Cambridge, Massachusetts. The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and ability to transition from pilot-scale manufacturing to large-scale production of products. The Company had an accumulated deficit of $291.6 million as of December 31, 2018 and has financed its operations to date from proceeds obtained from its IPO, subsequent offerings of its common shares in January 2018 and September 2018, a series of preferred shares and convertible loan issuances, and upfront fees received under its collaboration and joint venture arrangements. The Company will require substantial additional capital to fund its research and development and ongoing operating expenses. Liquidity In January 2018, the Company completed an offering of 5,750,000 shares of common shares, which were sold at a price of $22.75 per share. This offering resulted in net proceeds of $122.6 million. In August 2018, the Company entered into an At-The-Market (“ATM”) sales agreement with LLC (“Jefferies”), under which the Company may offer and sell from time to time common shares having aggregate gross proceeds of up to $125.0 million. The Company has not yet issued or sold any securities under this sales agreement. In September 2018, the Company completed an offering of 4,210,526 common shares, which were sold at a price to the public of $47.50 per share. This offering resulted in net proceeds of $187.6 million. In addition, the issuance proceeds from the January and September offerings were further reduced by $3.1 million of stamp taxes, which were recorded as an offset to additional paid in capital.

Summary of Significant Accounti

Summary of Significant Accounting Policies and Basis of Presentation	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Basis of Presentation	2. Summary of Significant Accounting Policies and basis of presentation Basis of Presentation and Use of Estimates The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of (i) the Company, (ii) its wholly-owned subsidiaries, CRISPR Therapeutics Ltd., CRISPR Therapeutics Inc., CTX Financing GmbH, and TRACR Hematology Ltd., as of December 31, 2018. All intercompany accounts and transactions have been eliminated. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Investments in partnerships where the Company has significant influence because it has a voting interest of 20% to 50%, are accounted for under the equity method. Results of associated companies are presented on a one-line basis. The Company accounts for its 50% investment share of Casebia Therapeutics LLP (“Casebia”) under the equity method of accounting. See Note 9 for further details. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, equity-based compensation expense, revenue recognition, equity method investments, and reported amounts of expenses during the reported period. Significant estimates in these consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses, valuation of equity method of investment, equity-based compensation expense, fair value of Common Shares, and the provision for or benefit from income taxes. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company and the Company’s chief operating decision maker, namely, the chief executive officer, view the Company’s operations and manage its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology. Foreign Currency Translation and Transactions The Company’s reporting currency is the U.S. Dollar. The Company‘s consolidated entities have the U.S. dollar as their functional currency with the exception of CRISPR Ltd. which has the British Pound Sterling (“GBP”) as its functional currency. CRISPR Ltd. has assets and liabilities translated into U.S. dollars at exchange rates in effect at the end of the year. Revenue and expenses are translated using the average exchange rates for the period. Net unrealized gains and losses resulting from foreign currency translation are included in accumulated other comprehensive loss, which is a separate component of shareholders’ equity. Net foreign currency exchange transaction gains and losses resulting from the remeasurement of transactions denominated in currencies other than functional currency are included in other (expense) income, net in the consolidated statements of operations and comprehensive loss. Cash and Cash Equivalents The Company considers all highly liquid investments with maturities of 90 days or less from the purchase date to be cash equivalents. As of December 31, 2018 and 2017, the Company had $456.6 million and $239.8 million in cash equivalents, respectively. The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. Restricted Cash In 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230) Restricted Cash As of December 31, 2018 2017 2016 Cash and cash equivalents 456,649 239,758 315,520 Restricted Cash 3,163 3,154 3,150 Total $ 459,812 $ 242,912 $ 318,670 Accounts Receivable Accounts receivable of $0.1 million and $2.6 million at December 31, 2018 and 2017, respectively, consist of receivables from Vertex Pharmaceuticals, Incorporated (“Vertex”) and Casebia. These amounts represent the balance due from the respective parties for the portion of our arrangements accounted for under ASC 606, Revenue from contracts with customers. Other Receivables Other receivables of $3.4 million and $1.9 million at December 31, 2018 and 2017, respectively, consists of receivables from Vertex and are included with prepaid and other expense in the consolidated balance sheet. These amounts represent the balance due from the portion of our arrangement accounted for under ASC 808, Collaborative Arrangements Concentrations of Credit Risk and Off-balance Sheet Risk Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash. The Company’s cash is held in accounts with financial institutions that management believes are creditworthy. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss. Fair Value of Financial Instruments The Company’s financial instruments consist of accounts payable, accrued expenses and other non-current liabilities. The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic 820, Fair Value Measurement and Disclosures The accounting standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value, which are the following: Level 1 — Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities. Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying amount of accounts receivable, other receivables, accounts payable, and accrued expenses as reported on the consolidated balance sheets as of December 31, 2018 and 2017, approximate fair value, due to the short-term duration of these instruments. The fair value of the Company’s equity method investment in Casebia was determined using level 3 inputs (See Note 9). Property and Equipment Property and equipment is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Computer equipment 3 years Furniture, fixtures, and other 5 years Laboratory equipment 5 years Leasehold improvements Shorter of useful life or remaining lease term Impairment of Long-lived Assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book value of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value. The Company has not recognized any impairment losses in the years ended December 31, 2018, 2017, and 2016. Revenue Recognition In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which supersedes existing revenue recognition guidance. The Company adopted ASU 2014-09 and its related amendments (collectively known as “ASC 606”) on January 1, 2018 using the modified retrospective method, by recognizing the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of equity at January 1, 2018. The reported results for 2018 reflect the application of ASC 606 guidance while the reported results for 2017 and prior were prepared under the guidance of ASC 605, Revenue Recognition (“ASC 605”). The Company has elected a practical expedient and applied ASC 606 only to contracts that are not completed at the date of initial application. ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. The Company’s revenue is from collaboration agreements. Within collaboration agreements, a counterparty may be a collaborator or partner that shares in the risks and benefits of developing a product to be marketed. These arrangements generally are in the scope of ASC 808, Collaborative Arrangements (“ASC 808”) yet may also contain vendor-customer aspects. Therefore, the Company considers all of the facts and circumstances to determine which transactions have a vendor-customer relationship that is subject to ASC 606. At the inception of each agreement the Company must determine which promised goods and services are under the scope of ASC 606 versus ASC 808 (discussed in the Collaborative Arrangements note below). In accordance with ASC 606, revenue is recognized when a customer obtains control of promised goods or services. The amount of revenue recognized reflects the consideration to which the Company expects to be entitled to receive in exchange for these goods and services. To achieve this core principle, the Company applies the following five steps: 1) Identify the contract with the customer A contract with a customer exists when (i) the Company enters into an enforceable contract with a customer that defines each party’s rights regarding the goods or services to be transferred and identifies the related payment terms, (ii) the contract has commercial substance, and (iii) the Company determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration. 2) Identify the performance obligations in the contract Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the good or service either on its own or together with other available resources, and are distinct in the context of the contract, whereby the transfer of the good or service is separately identifiable from other promises in the contract. To the extent a contract includes multiple promised goods and services, the Company must apply judgment to determine whether promised goods and services are capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation. 3) Determine the transaction price The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes. Determining the transaction price requires significant judgment, which is discussed in further detail for each of the Company’s contracts with customers in Note 9. 4) Allocate the transaction price to performance obligations in the contract If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. 5) Recognize revenue when or as the Company satisfies a performance obligation The Company satisfies performance obligations either over time or at a point in time. Revenue is recognized over time if either 1) the customer simultaneously receives and consumes the benefits provided by the entity’s performance, 2) the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced, or 3) the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer. Examples of control are using the asset to produce goods or services, enhance the value of other assets, settle liabilities, and holding or selling the asset. ASC 606 requires the Company to select a single revenue recognition method for the performance obligation that faithfully depicts the Company’s performance in transferring control of the goods and services. The guidance allows entities to choose between two methods to measure progress toward complete satisfaction of a performance obligation: 1. Output methods - recognize revenue on the basis of direct measurements of the value to the customer of the goods or services transferred to date relative to the remaining goods or services promised under the contract (e.g. surveys of performance completed to date, appraisals of results achieved, milestones reached, time elapsed, and units of produced or units delivered); and 2. Input methods - recognize revenue on the basis of the entity’s efforts or inputs to the satisfaction of a performance obligation (e.g., resources consumed, labor hours expended, costs incurred, or time elapsed) relative to the total expected inputs to the satisfaction of that performance obligation. The Company has the right to consideration from a customer in an amount that corresponds directly with the value to the customer of the entity’s performance completed to date (i.e. R&D services), as such the Company has elected a practical expedient to recognize revenue in the amount to which the entity has a right to invoice for such services. The terms of the Company’s collaboration and license agreements contain multiple promised goods and services, which include options to license CRISPR/Cas9-based therapeutic products directed to specific targets, referred to as co-exclusive or exclusive licenses, joint steering committee participation, as well as research and development activities to be performed by the Company on behalf of the collaboration partner related to the licensed targets. Payments that the Company may receive under these agreements include nonrefundable upfront fees, payments for research activities, payments based upon the achievement of specified milestones and royalties on any resulting net product sales. To date, the Company’s only source of revenue has been the collaboration and license and joint development and commercialization agreement with Vertex as well as research and development services provided to Casebia under the joint venture with Bayer HealthCare LLC (“Bayer”). Please refer to Note 9 for the specific accounting treatment and revenue recognized during the period for each of these arrangements. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company must consider the nature of the intellectual property to which the customer will have rights (i.e. access at a point in time or benefit of intellectual property enhancements over time). The Company recognizes revenue from non-refundable, up-front fees allocated to the license at a point in time/over the period the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments: At the inception of each arrangement that includes development, regulatory or commercial milestone payments for promised goods and services, the Company evaluates the circumstances of whether the milestones will be reached and estimates the amount to be included in the transaction price that will not cause a significant revenue reversal. The Company will evaluate these types of payments for customer options once those options have been exercised. ASC 606 suggests two alternatives to use when estimating the amount of variable consideration: the expected value method and the most likely amount method. Under the expected value method, an entity considers the sum of probability-weighted amounts in a range of possible consideration amounts. Under the most likely amount method, an entity considers the single most likely amount in a range of possible consideration amounts. The Company will use the most likely amount method for development and regulatory milestone payments. Management believes the most likely amount method is the better predictor as the Company expects to be entitled to only one of two possible amounts. Additionally, management believes that the most likely amount of milestone consideration is its stated amount. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. The transaction price is then allocated to performance obligations on a specific basis or on a relative stand-alone selling price basis. The Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates whether it is probable that a significant revenue reversal will not occur in future periods, and if necessary, adjusts its estimates of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). Up-front payments and fees are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Contract Balances The Company recognizes a contract asset when the Company transfers goods or services to a customer before the customer pays consideration or before payment is due, excluding any amounts presented as a receivable (i.e. accounts receivable). A contract asset is an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer. The contract liabilities (i.e. deferred revenue) primarily relate to contracts where we have received payment but we have not yet satisfied the related performance obligations. The advance consideration received from customers for R&D services or licenses bundled with other promises is a contract liability, recorded as deferred revenue, until the underlying performance obligations are transferred to the customer. The change in deferred revenue from December 31, 2017 to December 31, 2018 is primarily related to the transition adjustment upon the adoption of ASC 606. Income Taxes The adoption of ASC 606 resulted in a reduction of cumulative revenue as of January 1, 2018, which in turn generated additional deferred tax assets. As the Company fully reserves its net deferred tax assets in the jurisdictions impacted by the adoption of ASC 606, this impact was offset by a corresponding change to the valuation allowance. Impact of Adopting ASC 606 on the Financial Statements The Company adopted ASC 606 using the modified retrospective method. The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018 was recorded as an adjustment to accumulated deficit as of the adoption date. The Company elected to apply a practical expedient to reflect the aggregate effect of all modifications that occur before the beginning of the earliest period presented when identifying the satisfied and unsatisfied performance obligations, determining the transaction price, and allocating the transaction price to the satisfied and unsatisfied performance obligations. As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made to the consolidated balance sheet as of January 1, 2018: As Reported December 31, 2017 ASC 606 Adjustment Adjusted January 1, 2018 Consolidated Balance Sheet Data (in thousands): Other current liabilities $ 137 $ 102 $ 239 Total current liabilities $ 14,511 $ 102 $ 14,613 Deferred revenue $ 56,928 $ 1,046 $ 57,974 Total liabilities $ 83,514 $ 1,148 $ 84,662 Accumulated deficit $ (125,440 ) $ (1,148 ) $ (126,588 ) Total shareholders' equity $ 187,832 $ (1,148 ) $ 186,684 Total liabilities and shareholders’ equity $ 271,346 $ — $ 271,346 Impact of New Revenue Guidance on Financial Statement Line Items The following table compares the reported condensed consolidated balance sheet, statement of operations and cash flows, as of and for the year ended December 31, 2018, to the pro-forma amounts had the previous guidance been in effect: As of December 31, 2018 As Reported Under ASC 606 Adjustments Notes Adjusted Balance Under ASC 605 Consolidated Balance Sheet Data (in thousands): Other current liabilities $ 221 $ (102 ) (5) $ 119 Total current liabilities $ 27,746 $ (102 ) (5) $ 27,644 Deferred revenue $ 57,780 $ (750 ) (1)(2)(3)(5) $ 57,030 Total liabilities $ 96,821 $ (852 ) (1)(2)(3)(5) $ 95,969 Accumulated deficit $ (291,569 ) $ 852 (1)(2)(3) $ (290,717 ) Total shareholders' equity $ 392,195 $ 852 (1)(2)(3) $ 393,047 Total liabilities and shareholders’ equity $ 489,016 $ — (1)(2)(3) $ 489,016 Year Ended December 31, 2018 Consolidated Statement of Operations Data (in thousands): As Reported Under ASC 606 Adjustments Notes Adjusted Balance Under ASC 605 Collaboration revenue $ 3,124 $ (296 ) (2)(3) $ 2,828 Loss from operations $ (158,943 ) $ (296 ) (2)(3) $ (159,239 ) Net loss before income taxes $ (164,428 ) $ (296 ) (2)(3) $ (164,724 ) Net loss $ (164,981 ) $ (296 ) (2)(3) $ (165,277 ) Comprehensive loss $ (165,003 ) $ (296 ) (2)(3) $ (165,299 ) Consolidated Statement of Cash Flows (in thousands): Operating activities: Net loss $ (164,981 ) $ (296 ) (2)(3) $ (165,277 ) Reconciliation of net loss to net cash and restricted cash used in operating activities: Changes in: Deferred revenue $ (296 ) $ 398 (1)(2)(3)(4)(5) $ 102 Other liabilities, net $ 249 $ (102 ) (1)(2)(3)(4)(5) $ 147 Net cash and restricted cash (used in) operating activities $ (96,239 ) $ — $ (96,239 ) Increase (decrease) in cash and restricted cash $ 216,900 $ — $ 216,900 Cash and restricted cash, end of period $ 459,812 $ — $ 459,812 (1) Adjustment of $1,148 to reverse the ASC 606 transition adjustment from accumulated deficit and deferred revenue. (2) Adjustment of $194 for the year ended December 31, 2018, related to R&D services that would be deferred under ASC 605 versus recognized as invoiced under ASC 606. (3) Adjustment of $102 for the year ended December 31, 2018, related to non-exclusive research license revenue that would be recognized upon option exercise under ASC 605 versus recognized overtime under ASC 606. (4) Adjustment to reverse the ASC 606 transition adjustment to accumulated deficit and deferred revenue netted to zero as the transaction did not impact cash. (5) Adjustment to reclassify $102 from deferred revenue to other current liabilities (current deferred revenue) related to the change in revenue allocated to the non-exclusive research license recognized upon option exercise under ASC 605 versus ratably over time under ASC 606. Collaboration Arrangements The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC 808. Accordingly, the elements of the collaboration agreements that represent activities in which both parties are active participants and to which both parties are exposed to the significant risks and rewards that are dependent on the commercial success of the activities, are recorded as collaborative arrangements. The Company considers the guidance in ASC 606 in determining the appropriate treatment for the transactions between the Company and its collaborative partner and the transactions between the Company and third parties. Generally, the classification of transactions under the collaborative arrangements is determined based on the nature and contractual terms of the arrangement along with the nature of the operations of the participants. The Company evaluates the proper presentation of the commercial activities and the profit and loss sharing associated with the collaboration agreements. ASC 808 states that when payments between parties in a collaborative arrangement are not within the scope of other authoritative accounting literature, the income statement classification should be based on the nature of the arrangement, the nature of its business operations and the contractual terms of the arrangement. To the extent that these payments are not within the scope of other authoritative accounting literature, the income statement classification for the payments shall be based on an analogy to authoritative accounting literature or if there is no appropriate analogy, a reasonable, rational, and consistently applied accounting policy election. Research and Development Expenses Research and development costs, which include employee compensation costs, facilities, lab supplies and materials, overhead, preclinical development, and other related costs, are charged to expense as incurred. Research and development costs also include the costs the Company incurs in its performance of services or provision of materials in connection with the funded research undertaken as a part of the Company’s collaborative agreement with Vertex and Casebia. See Note 9 for further details. Operating Leases The Company leases office and laboratory facilities under a non-cancelable operating lease agreements. The lease agreements contain free or escalating rent payment provisions. The Company recognizes rent expense under such leases on a straight-line basis over the term of the lease with the difference between the expense and the payments recorded as deferred rent on the consolidated balance sheets. Lease renewal periods are considered on a lease-by-lease basis in determining the lease term. Funding of leasehold improvements by the Company’s landlord are accounted for as a tenant improvement allowance and are amortized as a reduction of rent expense over the term of the lease. Leasehold improvements are amortized straight-line over the shorter of the useful life or the remaining lease term. Equity Based Compensation Expense The Company recognizes equity-based compensation expense for awards of equity instruments to employees and non-employee directors based on the grant date fair value of those awards in accordance with FASB ASC Topic 718, Stock Compensation (“ASC 718”). ASC 718 requires all equity-based compensation awards to employees and non-employee directors, including grants of restricted shares and stock options, to be recognized as expense in the statements of operations based on their grant date fair values. The Company estimates the fair value of stock options using the Black-Scholes option pricing model. The Company uses the fair value of our Common Shares to determine the fair value of restricted share awards. Prior to July 1, 2018, the Company accounted for stock options issued to non-employees and employees of Casebia under FASB ASC Topic 505-50, Equity Based Payments to Non-Employees (“ASC 505-50”) through June 30, 2018. As such, the value of such options were periodically remeasured, and income or expense was recognized over their vesting terms. Compensation cost related to awards with service-based vesting schedules was recognized using the straight-line method. As of July 1, 2018, the Company adopted the FASB ASU No. 2018-07, Stock Compensation (“ASU 2018-07”) which provides improvements to nonemployee share-based payment accounting. ASU 2018-07 is intended to reduce the cost and complexity and to improve financial reporting for nonemployee share-based payments. The scope of ASC 718, which currently only includes share-based payments to employees was expanded to include share-based payments issued to nonemployees for goods or services. ASC 505-50, was superseded and consequently, the accounting for share-based payments to nonemployees and employees will be substantially aligned. As a result of adopting this standard, the fair value of outstanding nonemployee awards post adoption are no longer remeasured each reporting period and expense related to these awards was recorded ba

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Property and Equipment, net	3. Property and Equipment, net Property and equipment, net, consists of the following (in thousands): As of December 31, 2018 2017 Computer equipment $ 443 $ 285 Furniture, fixtures, and other 2,453 2,104 Laboratory equipment 8,964 6,603 Leasehold improvements 13,776 13,776 Construction work in process 239 0 Total property and equipment, gross 25,875 22,768 Accumulated Depreciation (7,375 ) (3,911 ) Total property and equipment, net $ 18,500 $ 18,857 Depreciation expense for the year ended December 31, 2018, 2017, and 2016 was $3.5 million, $3.0 million, and $0.9 million, respectively.

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Variable Interest Entities	4. Variable Interest Entities Joint Venture with Bayer Healthcare LLC In December 2015, the Company entered into an agreement with Bayer to create a joint venture to discover, develop and commercialize new therapeutics for genetically linked diseases, including blood disorders, blindness and heart disease. On February 12, 2016, Casebia, a limited liability partnership, was formed in the United Kingdom. In March 2016 upon consummation of the JV, Bayer and the Company each received a 50% equity interest in the entity in exchange for their contributions to the entity. The Company determined that Casebia was considered a VIE and concluded that it is not the primary beneficiary of the VIE. As such, the Company did not consolidate Casebia’s results into the consolidated financial statements. See Note 9 for further details.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Assets	5. Intangible Assets The Company’s intangible assets consist of acquired intellectual property rights related to the Company’s initial consolidation of TRACR in April 2014. Acquired intellectual property rights had an estimated life of 10 years. Intangible assets, net of accumulated amortization, are as follows (in thousands): Acquired intangible asset Cost Accumulated Amortization Net As of December 31, 2018 $ 547 $ (258 ) $ 289 As of December 31, 2017 $ 547 $ (203 ) $ 344 The Company recorded amortization expense of $0.1 million for each of the years ended December 31, 2018, 2017, and 2016, respectively. As of December 31, 2018 the remaining amortization period was 5.3 years. The Company has not recorded any impairment charges for the years ended December 31, 2018, 2017 and 2016. The estimated future amortization of acquired intangible assets as of December 31, 2018 is expected to be as follows (in thousands): For the Year Ended December 31, Amount 2019 55 2020 55 2021 55 2022 55 2023 55 Thereafter 14 Total amortization $ 289

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses consist of the following (in thousands): As of December 31, 2018 2017 Payroll and employee-related costs $ 7,321 $ 5,550 Research costs $ 7,973 2,285 Licensing fees $ 625 609 Professional fees $ 1,848 2,176 Intellectual property costs $ 2,193 500 Accrued property and equipment $ 294 — Other $ 598 241 Total $ 20,852 $ 11,361

Convertible Loans

Convertible Loans	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Convertible Loans	7. Convertible Loans 2015 Convertible Loan Agreement with Vertex and certain existing shareholders On October 26, 2015, the Company entered into a convertible loan agreement with Vertex and certain existing shareholders (the “Vertex Convertible Loan”) under which the Company could borrow up to $40.0 million. The Vertex Convertible Loan accrued interest at 2.5% per annum and had an initial maturity date of April 26, 2016 subject to acceleration upon the occurrence of certain conditions stated in the loan agreement. On various dates between November 23 and December 7, 2015, the Company borrowed aggregate net proceeds of $38.2 million. The Vertex Convertible Loan included various embedded conversion, redemption and other features, none of which required separate accounting from the host instrument under ASC 815, Derivatives and Hedging Convertible Loan with Bayer HealthCare LLC Concurrent with the execution of the Bayer Joint Venture agreement, the Company also entered into a Convertible Loan Agreement (“Bayer Convertible Loan”) with Bayer for $35.0 million. The Bayer Convertible Loan accrued interest at 2.0% per annum and matured on January 29, 2016 (the “Maturity Date”). On January 29, 2016, the Company issued the Bayer Convertible Loan in exchange for aggregate net proceeds of $35.0 million. The Bayer Convertible Loan included various embedded conversion, redemption and other features, none of which required separate accounting from the host instrument under ASC 815. Conversion of Convertible Loans to Series B Preferred Shares On January 29, 2016, concurrent with the issuance of the Bayer Convertible Loan, all of the outstanding principal under the $35.0 million Bayer Convertible Loan automatically converted into 2,605,330 Series B Preferred Shares at $ 13.43 The receipt of $35.0 million in proceeds under the Bayer Convertible Loan in exchange for equity securities, combined with the $38.2 million in proceeds from Vertex Convertible Loan, represented a qualified financing, as defined, and triggered an automatic conversion provision of the Vertex Convertible Loan Agreement. Accordingly, on January 29, 2016, the Vertex Convertible Loan, including loans from existing shareholders, plus accrued interest also converted into 2,859,278 of Series B Preferred Shares at $13.43 per share. The Company determined the fair value of the Vertex Convertible Loan to be $26.9 million based on the fair value of the underlying Series B Preferred Shares that were exchanged as part of the conversion. Upon extinguishment, the Company recorded a gain on extinguishment of $11.5 million for the difference between the carrying value of the debt and the fair value of the Series B Preferred Shares issued to settle the debt under the general extinguishment model.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Operating Leases As of December 31, 2018, the Company had operating In May 2016, the Company entered into a sublease pursuant to which it subleases in Cambridge, Massachusetts its Future minimum payments required under the leases as of December 31, 2018, are as follows (in thousands): Years Ended December 31, Amount 2019 $ 6,275 2020 6,866 2021 7,072 2022 5,874 2023 5,855 Thereafter 18,639 Total minimum lease payments $ 50,581 The amounts above are net of payment to be received under a sublease agreement, totaling $0.4 million in 2019. Letters of Credit As of December 31, 2018 and 2017, the Company had restricted cash of $3.2 million and $3.2 million, respectively, representing letters of credit securing the Company’s obligations under certain leased facilities in Cambridge, Massachusetts at 200 Sidney Street and the 610 Main Street as well as certain credit card arrangements. The letters of credit are secured by cash held in a restricted depository account. The cash deposit is recorded in restricted cash in the accompanying consolidated balance sheet as of December 31, 2018 and 2017. Shareholder Settlement Under the terms of a shareholder agreement existing prior to the IPO in 2016, if a U.S. common shareholder elected to file a Qualified Electing Fund (“QEF”) and notified the Company of this election, the Company was required to make advance payments to the shareholder related to their individual tax liability. In September 2016, the Company formally offered an aggregate settlement of up to $2.0 million to certain U.S common shareholders in order to release the Company from any and all obligations or claims concerning and/or arising out of the Company’s status as a PFIC or a Controlled Foreign Corporation (a “CFC”) for any taxable year from 2013 through 2015, including for potential lack of timely notification of the Company’s PFIC status (an “Annual Information Statement”) for the year ended December 31, 2015. Following the formal settlement offer in September 2016, in the fourth quarter of 2016 the Company made payments to shareholders of $2.0 million, respectively, under the terms of the accepted settlements. The obligation to make advance payments under the shareholder agreement for tax years subsequent to 2015 terminated upon the closing of the IPO. The Company has made available a 2018 and 2017 PFIC Annual Information Statement on its website for its shareholders. Research Agreements The Company has engaged several research institutions and companies to identify new delivery strategies and applications of the gene-editing technology. In association with these agreements, the Company has committed to making payments for related research and development services of $0.5 million, and $0.1 million in 2019 and 2020, respectively. The Company is also a party to a number of research license agreements which require significant upfront payments, future royalty payments and potential milestone payments from time to time. In association with these agreements, the Company has committed to making payments of $4.7 million and 2.8 million in 2019 and 2020, respectively. In addition, the Company is also a party to intellectual property agreements, which require maintenance and milestone payments from time to time. In association with these agreements, the Company has committed to making payments for maintenance and milestones of $0.4 million and $0.1 million in 2019 and 2020, respectively. The Company is a party to a number of manufacturing agreements that require upfront payments for the future performance of services. In connection with these agreements, the Company has made upfront payments and recorded $2.1 million as prepaid expenses on the condensed consolidated balance sheet as of December 31, 2018. The Company will amortize the prepaid balance as services are performed. Litigation The Company licenses a U.S. patent application from Emmanuelle Charpentier (as described in more detail in this Annual Report on Form 10-K) that was subject to interference proceedings declared by the Patent Trial and Appeal Board (“PTAB”) of the U.S. Patent and Trademark Office. Following motions by the parties and other procedural matters, the PTAB concluded in February 2017 that the declared interference should be dismissed because the claim sets of the two parties were not directed to the same patentable invention in accordance with the PTAB’s two-way test for patent interferences. In April 2017, Dr. Charpentier, the regents of the University of California (“UC”), and the University of Vienna (collectively “UC”) appealed the PTAB decision to the U.S. Court of Appeals for the Federal Circuit (“Federal Circuit”). In the appeal, UC asked the court to review and reverse of the PTAB’s February 2017 decision, which terminated the interference without determining which inventors actually invented the use of the CRISPR/Cas9 genome editing technology in eukaryotic cells. The Federal Circuit conducted a hearing on the appeal on April 30, 2018. On September 10, 2018, the Federal Circuit affirmed the PTAB’s decision to terminate the interference proceeding. In February 2018, several parties filed oppositions in the European Patent Office to the grant of the Company’s in-licensed European patent. Opposition proceedings can lead to the revocation of a patent in its entirety; the maintenance of the patent as granted, or the maintenance of a patent in amended form. Opposition proceedings typically take years to resolve, including the time taken by appeals that can be filed by any of the parties. The Company cannot guarantee the outcome of the oppositions to its in-licensed European patent, and an adverse result could preclude the Company from enforcing its rights in Europe against third parties. On December 15, 2016, the Company entered into a Consent to Assignments, Licensing and Common Ownership and Invention Management Agreement (the “Invention Management Agreement”) with the University of California, University of Vienna, Dr. Emmanuelle Charpentier, Intellia Therapeutics, Inc. Caribou Biosciences, Inc., ERS Genomics Ltd. and TRACR Hematology Ltd. Under the Invention Management Agreement, the Company is obligated to share costs related to patent maintenance, defense and prosecution. For the years ended December 31, 2018 and 2017, the Company incurred $2.4 million and $1.2 million, respectively, in shared costs. The Company recorded accrued legal costs from the cost sharing of $1.9 million and $0.4 million as of December 31, 2018 and December 31, 2017, respectively. No expense was incurred or accrued as for the year ended December 31, 2016. The Company is unable to predict the outcome of these matters and is unable to make a meaningful estimate of the amount or range of loss, if any, that could result from an unfavorable outcome .

Significant Contracts

Significant Contracts	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Significant Contracts	9. Significant Contracts Intellectual Property Agreements CRISPR Therapeutics AG—Charpentier License Agreement In April 2014, the Company entered into a technology license agreement with Dr. Emmanuelle Charpentier pursuant to which the Company licensed certain intellectual property rights under joint ownership from Dr. Charpentier to develop and commercialize products for the treatment or prevention of human diseases other than hemoglobinopathies (“CRISPR—Charpentier License Agreement”). In consideration for the granting of the license, the Company paid Dr. Charpentier an upfront fee of During the years ended December 31, 2018 and 2017, the Company did not record any sublicensing fees due to Dr. Charpentier in research and development expense related to the Bayer Joint Venture Agreement. During the year ended December 31, 2016, the sublicensing fees were immaterial. TRACR Hematology Limited—Charpentier License Agreement In April 2014, TRACR entered into a technology license agreement (“TRACR—Charpentier License Agreement”) with Dr. Emmanuelle Charpentier pursuant to which TRACR licensed certain intellectual property rights under joint ownership from Dr. Charpentier to develop and commercialize products for the treatment or prevention of human diseases related to hemoglobinopathies. In consideration for the granting of the license, Dr. Charpentier is entitled to receive nominal clinical milestone payments. TRACR is also obligated to pay Dr. Charpentier a low single digit percentage of sublicensing payments received under any sublicense agreement with a third party. In addition, TRACR is obligated to pay to Dr. Charpentier low single digit percentage royalties based on annual net sales of licensed products and licensed services by the Company and its affiliates and sublicensees. During each of the years ended December 31, 2018, 2017, and 2016 the Company recorded an immaterial amount of sublicensing fees due to Dr. Emmanuelle Charpentier in research and development expense under the terms of the TRACR—Charpentier License Agreement that was triggered by the execution of the Vertex collaboration agreements. Invention Management Agreement On December 15, 2016, the Company entered into an IMA, with the University of California (“California”), the University of Vienna (“Vienna”), Dr. Charpentier, Intellia therapeutics, Inc. (“Intellia”), Caribou Biosciences, Inc. (“Caribou”), ERS Genomics Ltd., or (“ERS”), and TRACR. Under the IMA, California and Vienna retroactively consent to Dr. Charpentier’s licensing of her rights to the CRISPR/Cas9 intellectual property, pursuant to the license the Company has with Dr. Charpentier, to the Company, and wholly-owned subsidiary TRACR, and ERS, in the United States and globally. The IMA also provides retroactive consent of co-owners to sublicenses granted by us, TRACR and other licensees, prospective consent to sublicenses they may grant in future, retroactive approval of prior assignments by certain parties, and provides for, among other things, (i) good faith cooperation among the parties regarding patent maintenance, defense and prosecution, (ii) cost-sharing arrangements, and (iii) notice of and coordination in the event of third-party infringement of the subject patents and with respect to certain adverse claimants of the CRISPR/Cas9 intellectual property. Unless earlier terminated by the parties, the IMA will continue in effect until the later of the last expiration date of the patents underlying the gene-editing technology, or the date on which the last underlying patent application is abandoned. Under the IMA the Company is obligated to share costs related to patent maintenance, defense and prosecution. For the years ended December 31, 2018, 2017, and 2016 the Company incurred $2.4 million, $1.2 million and $2.8 million respectively, in shared costs. The Company had accrued legal costs from the cost sharing of $1.9 million and $0.4 million as of December 31, 2018 and December 31, 2017, respectively. Patent Assignment Agreement In November 2014, the Company entered into a patent assignment agreement (“Patent Assignment Agreement”) with Dr. Emmanuelle Charpentier, Dr. Ines Fonfara, and Vienna (collectively, the “Assignors”), pursuant to which the Company was assigned all rights, title and interest in and to certain patent rights claimed in the U.S. Patent Application No.61/905,835. In consideration for the assignment of such rights, the Assignors are entitled to receive clinical milestone payments totaling up to €0.3 million (approximately $0.4 million) in the aggregate for the first human therapeutic product. The Company is also obligated to pay to the Assignors low single digit royalties based on annual net sales of licensed products and licensed services by the Company and its affiliates and sublicensees. During the years ended December 31, 2018 and 2017, the Company did not record any sublicensing fees due to the Assignors in research and development expense under the terms of the Patent Assignment Agreement that was triggered by the execution of the Vertex collaboration agreement and the Bayer Agreement. During the year ended December 31, 2016, the sublicensing fees were immaterial. Collaboration Agreement with and Joint Development Agreement with Vertex Pharmaceuticals, Incorporated Summary of Agreement On October 26, 2015, the Company entered into a strategic collaboration, option, and license agreement (as may be amended from time to time, “Collaboration Agreement”) with Vertex, focused on the use of CRISPR’s gene editing technology, known as CRISPR/Cas9, to discover and develop potential new treatments aimed at the underlying genetic causes of human disease. On December 12, 2017, the Company and Vertex entered into Amendment No. 1 to the Collaboration Agreement (the “Amendment”) and the Joint Development Agreement (the “JDA”). The Amendment, among other things, modified certain definitions and provisions of the Collaboration Agreement to make them consistent with the JDA and clarified how many options are exercised (or deemed exercised) in connection with certain targets specified under the Collaboration Agreement. The Amendment also amended other provisions of the Collaboration Agreement, including the expiration terms of the Collaboration Agreement. In connection with the Collaboration Agreement, Vertex made a nonrefundable upfront payment of $75.0 million. Under the Collaboration Agreement, Vertex will fund all of the discovery activities conducted pursuant to the agreement while retaining options to co-exclusive and exclusive licenses. In December 2017, upon execution of the JDA and Amendment, Vertex exercised its option to obtain a co-exclusive license to develop and commercialize hemoglobinopathy and beta-globin targets. As such, for potential hemoglobinopathy treatments, including treatments for sickle cell disease, the Company and Vertex will share equally all research and development costs and worldwide revenues. For other targets that Vertex elects to license, Vertex will lead all development and global commercialization activities. For each of up to four remaining targets that Vertex elects to license, the Company has the potential to receive up to $420.0 million in development, regulatory and commercial milestones and royalties on net product sale. In connection with entering into the JDA, the Company received a $7.0 million up-front payment from Vertex and is eligible for a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate. The net profits and net losses, as applicable, incurred under the JDA will be shared equally between the Company and Vertex. Accounting for the Collaboration Agreement, Amendment and JDA under ASC 606 As the overall arrangement was modified in December 2017, the Company applied the practical expedient in ASC 606-10-65-1 in identifying the satisfied and unsatisfied performance obligations, determining the transaction price and allocating the transaction price under the practical expedient in ASC 606. The arrangement includes components of a customer-vendor relationship and a collaborative arrangement as defined under ASC 808. The Company will apply the guidance of ASC 606 by analogy to the vendor-customer performance obligations of the Collaboration Agreement and the performance obligations of the JDA subject to ASC 606 as outlined below. The Company will apply the guidance of ASC 808 to those elements in which there is a collaboration relationship in which both parties share equally in the risks and rewards of the research and development which include (i) development and commercialization services for currently identified shared products; (ii) R&D services for any follow-on products subject to the JDA; and (iii) committee participation. The Company evaluated the Collaboration Agreement, Amendment and JDA in accordance with the provisions of ASC 606. The Company identified the following performance obligations: (i) the non-exclusive research license; (ii) four material rights representing the option for up to four exclusive licenses to develop and commercialize the collaboration targets; (iii) a combined performance obligation representing the co-exclusive research license, and a development and commercialization license to develop and commercialize hemoglobinopathies and beta-globin targets; and (iv) the performance of R&D Services. The selling price of each performance obligation was determined based on the Company’s estimated standalone selling price (the “ESSP”). The Company developed the ESSP for all the performance obligations included in the Collaboration Agreement and JDA with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The ESSP for material rights was determined based on the incremental discount given to Vertex based on the ESSP of the four remaining exclusive licenses and the exercise price paid at the time of exercise. The Company developed the ESSP for the R&D Services primarily based on the nature of the services to be performed and estimates of the associated effort and cost of the services, adjusted for a reasonable profit margin that would be expected to be realized under similar contracts. The Company’s ESSP for the satisfied and unsatisfied R&D Services was $19.3 million. The Company’s ESSP for each of the remaining material rights to obtain an exclusive license to develop and commercialize a single collaboration target are $45.6 million, $38.4 million, $17.3 million and $17.3 million for a total of $118.6 million. ESSPs for these items were determined based on probability and present value adjusted cash flows from the milestones payments owed for exclusive licenses outlined in the Collaboration Agreement less the price paid to exercise the material right option. ESSP reflects the level of risk and expected probability of success inherent in the nature of the associated research area. The Company’s ESSP for the co-exclusive research license and the development and commercialization licenses for of the hemoglobinopathy and beta-globin targets is $48.9 million. ESSP for this item was determined based on probability and present value adjusted cash flows from the equal sharing of projected worldwide net profit or net loss. ESSP reflects the level of risk and expected probability of success inherent in the nature of the associated research area. The Company used a market-based approach to determine the ESSP of the non-exclusive research license of $1.0 million. The Company determined ESSP by use of comparative data, including in-licensed research agreements negotiated and executed within the Company. As the Company has a right to consideration from Vertex in an amount that corresponds directly with the value of the Company’s performance completed to date for the R&D services, thus the Company will recognize revenue related to the R&D services as invoiced, in line with the practical expedient in ASC 606-10-55-18. The transaction price is comprised of: (i) original upfront payment of $75.0 million, (ii) an upfront payment of $7.0 million under the JDA, and (iii) $19.3 million of variable consideration associated with the R&D services. The R&D services revenue will be recognized as invoiced and specifically allocated to the R&D services performance obligation. The remaining transaction price of $82.0 million was allocated among the performance obligations using the relative selling price method as follows: (i) a non-exclusive research license: $0.5 million; (ii) a material right to discounts for exclusive licenses for up to four Collaboration Targets: $22.2 million, $18.7 million, $8.4 million and $8.4 million for a total of $57.7 million; and (iii) co-exclusive development and commercialization licenses for hemoglobinopathy and beta-globin targets identified in the JDA and co-exclusive research license for the follow-on products: $23.8 million. The Company determined that the non-exclusive research license is symbolic intellectual property as Vertex receives value from the license through the Company’s ongoing activities, as such, the revenue related to the non-exclusive research license is recognized ratably over the term of the arrangement. Upon the execution of the JDA, a co-exclusive research, development and commercialization license was granted for hemoglobinopathy and beta-globin targets. The Company determined that the revenue related to these licenses was recognized at a point in time, in which they were delivered at inception of the JDA in December 2017. As Vertex has material right in its option to obtain four additional exclusive licenses to develop and commercialize four additional collaboration targets, the Company determined that consideration allocated to these material rights would be included in the transaction price of the exclusive license and recognized at a point in time, upon the exercise of the option by Vertex or expiration. Accounting for the Collaboration Agreement, Amendment and JDA under ASC 605 Under ASC 605, the Company evaluated the Collaboration Agreement, Amendment and JDA in accordance with the provisions of ASC 605-25. The Company’s arrangement with Vertex contains the following deliverables: (i) a non-exclusive research license; (ii) an option to obtain an exclusive license for up to four Collaboration Targets; (iii) co-exclusive development and commercialization licenses for hemoglobinopathy and beta-globin targets identified in the JDA; (iv) co-exclusive research license for the follow-on products; (v) the performance of R&D Services under the Collaboration Agreement; and (vi) JRC participation under the Collaboration Agreement. Management considered whether any of these deliverables could be considered separate units of accounting. Regarding the non-exclusive research license, the Company concluded that it does not have stand-alone value separate from the options to exercise the exclusive or the exercised co-exclusive licenses since Vertex would not benefit from acquiring a research license without the ability to obtain the license to commercialize the results of that research. As a result, the Company concluded that the research license should be combined with those options. Regarding the co-exclusive research license for the follow-on products, the Company concluded that it does not have stand-alone value separate from the exercised co-exclusive licenses under the JDCA since Vertex would not benefit from acquiring a research license without the license to commercialize the results of that research. The Company concluded the co-exclusive research license should be combined separately with each development and commercialization co-exclusive license granted under the JDA. Regarding the R&D Services under the Collaboration Agreement, the Company concluded that there are other vendors in the market that could perform the related services. As such the Company concluded the R&D Services represent a separate unit of accounting. Regarding the JRC obligations, the Company concluded that the JRC obligations deliverable has standalone value from the option to license because the services could be performed by an outside party. As such the Company concluded the JRC obligations represent a separate unit of accounting. As a result, management concluded that there following the modification are four units of accounting: (i) four individual combined units of accounting representing the non-exclusive research license, and the option for up to four exclusive licenses to develop and commercialize the collaboration targets; (ii) four individual combined units of accounting representing the co-exclusive research license, and a development and commercialization license to develop and commercialize hemoglobinopathies and beta-globin targets; (iii) the performance of R&D Services; and (iv) the participation in the JRC. The Company determined that neither VSOE of selling price nor TPE of selling price is available for any of the units of accounting identified. Accordingly, the selling price of each unit of accounting was determined based on the Company’s BESP. The Company developed the BESP for all of the units of accounting included in the Collaboration Agreement and JDA with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The Company developed the BESP for the R&D Services and the JRC participation primarily based on the nature of the services to be performed and estimates of the associated effort and cost of the services, adjusted for a reasonable profit margin that would be expected to be realized under similar contracts. The Company’s BESP for the remaining R&D Services was $4.0 million. The Company’s BESP for the JRC participation services was de minimis based on an estimate of time spent on preparation, participation, review and travel for the meetings. The Company’s BESP for the remaining four combined units of the non-exclusive research license and the options for an exclusive license to develop and commercialize a single collaboration target are $55.6 million, $48.4 million, $27.3 million and $27.3 million for a total of $158.6 million. BESPs for these items were determined based on probability and present value adjusted cash flows from the milestones payments owed for exclusive licenses outlined in the Collaboration Agreement. BESP reflects the level of risk and expected probability of success inherent in the nature of the associated research area. The Company’s BESP for the co-exclusive research license and the development and commercialization licenses for of the hemoglobinopathy and beta-globin targets is $48.9 million. BESP for this item was determined based on probability and present value adjusted cash flows from the equal sharing of project worldwide net profit or net loss. BESP reflects the level of risk and expected probability of success inherent in the nature of the associated research area. Allocable arrangement consideration is comprised of: (i) deferred revenue of $80.0 million; (ii) an upfront payment of $7.0 million under the JDA; (iii) the estimated R&D services of $4.0 million; and (iv) payments related to the estimated exercise of options on future exclusive licenses for four targets of $40.0 million. The aggregate allocable arrangement consideration of $131.0 million was allocated among the separate units of accounting using the relative selling price method as follows: (i) four individual combined units of accounting representing the non-exclusive research license, and the option for up to four exclusive licenses to develop and commercialize the collaboration targets: $34.4 million, $30.0 million, $16.9 million and $16.9 million for a total of $98.2 million; (ii) four individual combined units of accounting representing the co-exclusive research license, and a development and commercialization license to develop and commercialize each of the hemoglobinopathy and beta-globin targets: $30.3 million; and (iii) the performance of R&D Services: $2.5 million. Upon the execution of the JDA in December 2017, a research, development and commercialization license has been granted for hemoglobinopathy and beta-globin targets. The Company determined that these licenses were delivered at inception of the JDA and $30.3 million in revenue was recognized for this unit of accounting in December 2017. Milestones under the Collaboration Agreement The Company has evaluated all of the milestones that may be received in connection with the Collaboration Agreement and JDA. The first potential milestone the Company will be entitled to receive is the milestone in the JDA to receive a one-time low seven-digit milestone payment in any clinical trial in the initial shared product and is currently fully constrained. The remaining milestones are predominately related to the development and commercialization of a product resulting from the arrangement and are payable with respect to each selected exclusive license which have yet to be exercised and are not currently included in the determination of the transaction price. Each milestone is payable only once per collaboration target, regardless of the number of products directed to such collaboration target that achieve the relevant milestone event. There are nine remaining clinical development and regulatory approval milestones which may trigger proceeds of up to $90.0 million and $235.0 million, respectively, for each selected exclusive license, and two commercial milestones which may trigger proceeds of up to $75.0 million for each selected exclusive license (which, when combined with the $10.0 million due upon exercise of the exclusive option and the $10.0 million development milestone associated with an Investigational New Drug- enabling application, total $420.0 million for each selected Exclusive License), as follows: Developmental 1. Initiation of the first Clinical Trial of a Product 2. Establishment of POC for a Product 3. Initiation of the first Phase 3 Clinical Trial of a Product 4. Acceptance of Approval Application by the FDA for a Product 5. Acceptance of Approval Application by the EMA for a Product 6. Acceptance of Approval Application by a Regulatory Authority in Japan for a Product 7. Marketing Approval in the US for a Product 8. Marketing Approval in the EU for a Product 9. Marketing Approval in Japan for a Product Commercial Milestone Events 1. Annual Net Sales for Products with respect to a Collaboration Target exceed $500 million 2. Annual Net Sales for Products with respect to a Collaboration Target exceed $1.0 billion There is uncertainty that the events to obtain the developmental milestones will be achieved given the nature of clinical development and the stage of the gene-editing technology. Upon exercise of the exclusive license options, developmental milestones will be constrained until the Company is sure that a significant revenue reversal will not occur. Commercial milestones and royalties relate predominantly to a license of intellectual property and are determined by sales or usage-based thresholds. The commercial milestones and royalties will be accounted for under the royalty recognition constraint and will be accounted for as constrained variable consideration. The Company will apply the royalty recognition constraint for each commercial milestone and will not recognize revenue for each until the subsequent sale of a licensed product (achievement of each) occurs. Collaborative elements The Company evaluated the Collaboration Agreement, Amendment and JDA in accordance with the provisions of ASC 808. The Company identified the following elements of ASC 808: (i) development and commercialization services for shared products; (ii) R&D services for follow-on products; and (iii) committee participation. The Company evaluated that the nature of the arrangement and determined the arrangement is a cost/profit sharing arrangement and not a revenue arrangement. Therefore, the related impact of the cost sharing associated with research and development will be included in R&D expense. Expenses related to services performed by the Company will be classified as R&D expense. Payments received from Vertex for partial reimbursement of expenses are recorded as a reduction of R&D expense. During the years ended December 31, 2018, 2017 and 2016, the Company recognized $0.6 million, $36.2 million and $4.0 million of revenue related to the collaboration with Vertex, respectively. During the years ended December 31, 2018, 2017 and 2016, the Company recognized research and development expense of $20.2 million, $9.9 million and $7.0 million, respectively. Research and development expense for 2018 is net of $13.8 million of reimbursements from Vertex. As of December 31, 2018 and 2017, there was $57.8 million and $57.9 million of non-current deferred revenue related to the Collaboration Agreement, respectively Joint Venture with Bayer Healthcare LLC On December 19, 2015, the Company entered into an agreement with Bayer, to establish a joint venture (“Bayer Joint Venture”) to focus on the research the development of new therapeutics to cure blood disorders, blindness, and congenital heart disease. On February 12, 2016, the Company and Bayer completed the formation of the joint venture entity, Casebia, a limited liability partnership formed in the United Kingdom. Bayer and the Company each received a 50% equity interest in the entity in exchange for their respective contributions to the entity. The Company contributed $0.1 million in cash and licensed its proprietary CRISPR/Cas9 gene editing technology and intellectual property for selected disease indications. Bayer contributed its protein engineering expertise and relevant disease know-how. Under the agreement, Casebia has paid the Company $35.0 million in exchange for a worldwide, exclusive license to commercialize the Company’s gene-editing technology specifically for the indications covered by the license. There are no milestone, royalties or other payments due to the Company under this aspect of the agreement. The Company determined that the contribution of the CRISRP/Cas9 technology by license to Casebia did not meet the definition of a business under ASC 805. The Company also entered into a separate services agreement with Casebia, under which the Company agreed to provide compensated research and development services. Concurrent with the execution of the Bayer Joint Venture agreement, the Company also issued a convertible note to Bayer BV (the “Bayer Convertible Loan”) for gross proceeds of $35.0 million which was immediately converted to the Company’s Series B Preferred Shares at a conversion price of $13.43 per share. Concurrent with the Company’s initial public offering in October 2016, the Company issued and sold 2,500,000 common shares to Bayer BV, at the public offering price of $14.00 per share, resulting in aggregate net proceeds of $35.0 million. As the agreements relating to the Bayer Joint Venture (including the gene-editing technology license and the research and development services) and the Bayer Convertible Loan were executed at the same time, the Company determined that the contracts should be combined and evaluated as a single arrangement. Additionally, the Company also determined that ASC 845, Nonmonetary Transactions (“ASC 845”) did not apply to this arrangement given the Company’s significant continuing involvement with Casebia and the amount of cash involved in the arrangement. As a result, the Company analogized to the guidance within ASC 606 regarding the allocation of arrangement consideration, however elements under transaction that were not in the scope of ASC 606 were accounted for under accounting literature based on the allocated arrangement consideration. The Company determined the total consideration to be allocated to various elements of the transaction includes (i) the total cash payment by Casebia for the technology access fee, net of the Company’s $0.1 million contribution, of $34.9 million, (ii) the fair value of the equity interest in the Joint Venture of $36.4 million, (iii) the $35.0 million received from the issuance of the Bayer Convertible Loan, and (iv) $6.3 million of estimated cash consideration to be received under the research and development service arrangement, accumulating to $112.6 million. Under ASC 606 and ASC 605, the Company identified the following performance obligations in the combined transaction: (i) Combined element of an exclusive, worldwide, royalty free, license to the gene-editing technology specifically for the indications designated by Casebia, and delivery of the consents of the assignors of the underlying patents to the technology to develop, manufacture, and commercialize licensed products under that license (ii) Research and development services, and (iii) The Company also identified the issuance of the Bayer Convertible Loan as another element to be accounted for under ASC 470, Debt. For ASC 606, the Company allocated consideration to the performance obligations and other elements based on the relative proportion of their estimated standalone selling prices. The Company determined the standalone selling price of the license was $71.4 million based on the consideration paid and the fair value of the 50% interest in Casebia, which was determined utilizing discounted cash flows based on reasonable estimates and assumptions of cash flows expected from Casebia. The estimated standalone selling prices of the separate research and development services was determined to be $6.3 million and of the fair value of the Bayer Convertible Loan was determined to be $24.5 million, based on the fair value of the underlying preferred shares that were exchanged as part of the immediate conversion. Using a relative standalone selling price allocation, the Company allocated the aggregate arrangement consideration paid as follows (i) $79.1 million was allocated to the license and patent holder consent combined element; (ii) $27.2 million was allocated to the Bayer Convertible Loan. The difference between combined above amounts of $106.3 million and the total transaction price of $112.6 million is due to variable consideration of $6.3 million associated with the research and development service arrangement. The amount of the transaction price related to the research and development services ($6.3 million) will be allocated specifically to the research and development performance obligation under the right to invoice practical expedient in ASC 606-10-55-18. The combined amount attributed to the license and patent holder consent element of $79.1 million was recognized as other income for the year ended December 31, 2016. Under ASC 605, the Company determined the fair value of the license was $71.4 million based on the consideration paid and the fair value of the 50% interest in Casebia, which was determined utilizing discounted cash flows based on reasonable estimates and assumptions of cash flows expected from Casebia. The fair value of the separate research and development services was determined to be $6.3 million. The fair value of the Bayer Convertible Loan was determined to be $24.5 million, based on the fair value of the underlying preferred shares that were exchanged as part of the immediate conversion. Using a relative fair value allocation, the Company allocated the aggregate arrangement consideration paid as follows: (i) $63.6 million was allocated to the license and patent holder consent combined element (ii) $0.6 million was allocated to the future research and development services (iii) $27.0 million was allocated to the Bayer Convertible Loan The difference between combined above amounts of $91.2 million and the total allocable arrangement consideration of $112.6 million is due to allocable arrangement consideration associated with the $6.3 million of estimated cash consideration to be received under the research and development service arrangement and the remaining $15.0 million of the license fee paid upon the delivery of the consent from the patent holders of the Company’s intellectual property. Following delivery of the patent holders’ consent, which occurred on December 17, 2016, the combined amount attributed to the license and patent holder consent element and the remaining $15.0 million license fee, which amount to $78.6 million, was recognized as other income for the year ended December 31, 2016. The Company had determined that the license and patent holder consent combined element did not meet

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Share Capital	10. Share Capital The Company had 52,183,139 and 41,092,969 Common Share Issuances In October 2016, the Company closed the sale of 4,429,311 of our common shares in our initial public offering, or the IPO, inclusive of 429,311 common shares sold by the Company pursuant to the partial exercise of an overallotment option granted to the underwriters in connection with the offering, at a price to the public of $14.00 per share. The aggregate net proceeds received by the Company from the offering were $53.7 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. Concurrent with the IPO, the Company issued and sold 2,500,000 common shares to Bayer BV, at the IPO price $14.00 per share, or (the “Concurrent Private Placement”), resulting in aggregate net proceeds of $35.0 million in accordance with the terms of our subscription agreement with Bayer BV. Additionally, the Company issued and subsequently reacquired the unexercised overallotment Common Shares of 170,689 at no cost. In January 2018, the Company completed an offering of 5,750,000 shares of our common shares, which were sold at a price of $22.75 per share. This offering resulted in net proceeds of $122.6 million. In September 2018, the Company completed an offering of 4,210,526 common shares, which were sold at a price to the public of $47.50 per share. This offering resulted in net proceeds of $187.6 million . In addition, the issuance proceeds from the January and September offerings were further reduced by $3.1 million of stamp taxes, which were recorded as an offset to additional paid in capital. In addition, in August 2018, the Company entered into an At-The-Market (“ATM”) sales agreement with Jefferies LLC (“Jefferies”), under which the Company may offer and sell from time to time common shares having aggregate gross proceeds of up to $125.0 million. The Company has not yet issued or sold any securities under this sales agreement. The Common Shares have the following characteristics: Voting Rights The holders of Common Shares are entitled to one vote for each Common Share held at all meetings of shareholders and written actions in lieu of meetings. Dividends The holders of Common Shares are entitled to receive dividends, if and when declared by the Board of Directors. As of December 31, 2018, no dividends have been declared or paid since the Company’s inception. Liquidation The holders of the Common Shares are entitled to share ratably in the Company’s assets available for distribution to shareholders in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or upon the occurrence of a deemed liquidation event.

Equity-based Compensation

Equity-based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity-based Compensation	11. Equity-based Compensation Option and Grant Plans In July 2016, the shareholders approved the 2016 Share Option and Incentive Plan (the “2016 Plan”) and in April 2015, the shareholders approved the 2015 option and grant plan (the “2015 Plan” collectively the “Plans”). Subsequent to the IPO, no further options shall be granted under the 2015 Plan. The Plans provide for the issuance of equity awards in the form of restricted shares, options to purchase Common Shares which may constitute incentive stock options (“ISOs”) or non-statutory stock options (“NSOs”), unrestricted stock unit grants, and qualified performance and market-based awards to eligible employees, officers, directors, non-employee consultants, and other key personnel. Terms of the equity awards, including vesting requirements, are determined by the Board, subject to the provisions of the Plans. Options granted by the Company typically vest over four years and have a contractual life of ten years. The Company’s Board of Directors and shareholders approved an increase in the number of common shares reserved for issuance under the Company’s Amended and Restated 2016 Stock Option and Incentive Plan of 2,012,684 options in May 2017 , and the Company’s Board of Directors approved an additional increase to the number of common shares reserved for issuance under the Company’s 2018 Stock Option and Incentive Plan of an additional 4,000,000 shares in May 2018. During the years ended December 31, 2016 and 2015, the Company also issued outstanding Common Shares previously held by Founders and Fay Corp. to employees and non-employees as equity-based compensation (“Founder Awards”), which are subject to repurchase by the Company upon termination of the holder’s service relationship with the Company as well as upon certain triggering events such as termination for cause, material breach of agreement and insolvency of the holder that generally lapse over a requisite service period of four years. All of these shares were vested as of December 31, 2018. Equity-Based Compensation Expense Stock-based compensation, measured at the grant date based on the fair value of the award, is typically recognized as expense ratably over the requisite service period . Stock-based compensation awards subject to performance-based vesting conditions are recognized over the requisite service period using the accelerated attribution method. The following table presents stock-based compensation expense in the Company’s Consolidated Statements of Operations: Years Ended December 31, 2018 2017 2016 Research and development $ 17,557 $ 8,800 $ 4,848 General and administrative $ 17,428 10,073 5,844 Loss from equity method investment $ 4,275 1,763 152 Total $ 39,260 $ 20,636 $ 10,844 Grant- Date Fair Value The Company estimated the fair value of each employee and non-employee stock option award on the grant date using the Black-Scholes option-pricing model based on the following assumptions: Years Ended December 31, 2018 2017 2016 Employees: Options granted 2,188,097 2,894,850 2,411,240 Weighted - average exercise price $ 51.82 $ 16.92 $ 12.19 Weighted-average grant date fair value $ 33.81 $ 10.86 $ 8.47 Assumptions: Weighted-average expected volatility 71.9 % 72.1 % 81.0 % Expected term (in years) 6.0 6.0 6.0 Weighted-average risk free interest rate 2.8 % 2.0 % 1.4 % Expected dividend yield 0.0 % 0.0 % 0.0 % Non employees: Options granted 21,500 104,997 215,710 Weighted- average exercise price $ 42.75 $ 18.74 $ 19.54 Weighted- average grant date fair value $ 34.74 $ 19.35 $ 17.38 Assumptions: Weighted average expected volatility 77.9 % 81.5 % 88.2 % Expected term (in years) 10.0 9.4 10.0 Weighted-average risk free interest rate 3.0 % 2.4 % 2.4 % Expected dividend yield 0.0 % 0.0 % 0.0 % The fair value of the restricted stock awards was determined based on the fair value of Common Stock on the grant date. Prior to the adoption of ASU 2018-07 on July 1, 2018, stock options issued to non-employees and employees of Casebia were marked to market at each reporting period. As of July 1, 2018, upon the adoption of ASU 2018-07, the fair value of outstanding nonemployee awards are no longer remeasured each reporting period and expense related to these awards was recorded based on the fair value measured as of June 30, 2018. Share Based Payment Activity Stock Options The following table summarizes stock option activity for employees and non-employees during the year ended December 31, 2018 (intrinsic value in thousands): Stock Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2017 6,262,339 $ 13.24 8.8 $ 64,120 Granted 2,209,597 $ 51.73 Exercised (946,131 ) $ 10.95 Cancelled or forfeited (836,494 ) $ 20.11 Outstanding at December 31, 2018 6,689,311 $ 25.42 8.3 68,572 Exercisable at December 31, 2018 2,541,789 $ 15.74 7.7 $ 38,486 Vested or expected to vest at December 31, 2018 (1) 6,689,311 $ 25.42 8.3 $ 68,572 (1) This represents the number of vested stock options as of December 31, 2018 plus the unvested outstanding options at December 31, 2018 expected to vest in the future. As of December 31, 2018, the Company expects to recognize total unrecognized compensation cost related to stock options of $83.3 During 2018 and 2017, the Company granted options to purchase 0 and 395,000 Common Shares, respectively, subject to performance-based vesting conditions. As of December 31, 2018, options to purchase 790,598 Common Shares subject to performance-based vesting conditions were vested, as performance conditions were achieved, and there were 261,135 options to purchase Common Shares subject to performance-based vesting conditions outstanding. During 2017, the Company also granted 150,000 stock options with market-based vesting conditions in which the recipient is eligible to receive between zero and 150,000 options to purchase Common Shares at the end of a four year service period based upon achieving a specified average stock price. As of December 31, 2018, no options to purchase Common Shares subject to market-based vesting conditions were vested ; however, 150,000 options were as the specified average stock price limits were achieved. During the years ended December 31, 2018 and 2017, the Company modified the terms of certain options held by departing employees, resulting in $3.8 million and $2.2 million of stock-based compensation expense, respectively. Restricted Stock The following table summarizes restricted stock activity for employees and non-employees during the year ended December 31, 2018: Reflected as outstanding upon vesting Reflected as outstanding upon grant date Total Weighted- Average Grant Date Fair Value Unvested restricted common shares at December 31, 2017 157,515 208,886 366,401 $ 8.49 Granted 251,500 — 251,500 $ 44.51 Vested (77,673 ) (168,613 ) (246,286 ) $ 7.58 Cancelled or forfeited (4,000 ) (40,273 ) (44,273 ) $ 8.51 Unvested restricted common shares at December 31, 2018 327,342 — 327,342 $ 36.72 During the years ended December 31, 2018 and 2017, the total fair value of restricted stock vested was $11.3 million and $8.3 million, respectively. At December 31, 2018, total unrecognized compensation expense related to unvested restricted stock was $10.2 million which the Company expects to recognize over a remaining weighted-average period of 1.9 years. During the year ended December 31, 2016, the Company and Fay Corp. transferred 290,400 Common Shares to a founder, 268,093 of which were subject to vesting conditions with a weighted average grant date fair value of $12.65 per share. The unvested Common Shares were subject to repurchase by the Company upon termination of the holder’s service relationship with the Company as well as upon certain triggering events such as termination for cause, material breach of agreement and insolvency of the holder. The shares fully vested in 2018. During the years ended December 31, 2018, 2017 and 2016, the Company recognized expense related to the Common Shares transferred to the Founder of $0.3 million, $0.8 million and $2.6 million, respectively.

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
401(k) Savings Plan	12. 401(k) Savings Plan The Company established a defined‑contribution savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”) in November 2016. The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. The Company contributed $0.6 million, $0.5 million and $0.1 million to the 401(k) Plan for the year ended December 31, 2018, 2017 and 2016, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes The Company is subject to U.S. federal and various state corporate income taxes as well as taxes in foreign jurisdictions for the foreign parent and where foreign subsidiaries have been established. Net loss before taxes For the years ended December 31, 2018, 2017 and 2016, the loss before provision for income taxes consist of the following (in thousands): Years Ended December 31, 2018 2017 2016 Domestic $ 5,966 $ 5,184 $ 3,322 Foreign (170,394 ) (71,792 ) (26,040 ) Total $ (164,428 ) $ (66,608 ) $ (22,718 ) The (provision for) benefit from income taxes consist of the following (in thousands): Years Ended December 31, 2018 2017 2016 Current income taxes: Federal $ (416 ) $ (1,533 ) $ (649 ) State (131 ) (42 ) 11 Foreign — 6 17 Total current income taxes (547 ) (1,569 ) (621 ) Deferred income taxes: Federal (6 ) (477 ) 30 State — 297 105 Foreign — — 2 Total deferred income taxes (6 ) (180 ) 137 Total income tax provision $ (553 ) $ (1,749 ) $ (484 ) A reconciliation of income tax expense computed at the statutory corporate income tax rate to the effective income tax rate for the years ended December 31, 2018, 2017 and 2016 is as follows: Years Ended December 31, 2018 2017 2016 Income tax expense at statutory rate 9.3 % 9.3 % 10.3 % State income tax, net of federal benefit 0.7 % 0.3 % 1.3 % Nondeductible expenses 0.0 % 0.0 % 1.6 % Foreign rate differential (0.4 %) (2.5 %) (3.3 %) Statutory to US GAAP permanent differences 1.0 % 1.8 % 6.6 % Stock-based compensation 1.4 % (2.9 %) (4.9 %) Research credits 1.8 % 0.8 % 3.1 % Change in valuation allowance (14.1 %) (9.4 %) (16.8 %) Effective income tax rate (0.3 %) (2.6 %) (2.1 %) The federal statutory rate reflects the Switzerland mixed company service rate. Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets are comprised of the following (in thousands): Years Ended December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 25,418 $ 9,987 Accruals and reserves 1,816 1,123 Deferred Rent 3,300 3,494 Other deferred tax assets 51 36 Stock based compensation 2,871 — Deferred revenue 3,264 1,721 Research credit 3,322 543 Total deferred tax assets 40,042 16,904 Less valuation allowance (36,208 ) (13,041 ) Net deferred tax assets 3,834 3,863 Deferred tax liabilities: Depreciation (3,785 ) (3,791 ) Intangible assets (49 ) (59 ) Other deferred tax liabilities (22 ) (31 ) Total deferred tax liabilities (3,856 ) (3,881 ) Long term deferred taxes $ (22 ) $ (18 ) The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of worldwide operating losses, the Company has concluded that it is more-likely-than-not that the benefit of its U.S. and non-U.S. deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance against its net deferred tax assets in Switzerland, U.S. and in the UK for its TRACR subsidiary, as of December 31, 2018 and 2017. The valuation allowance increased by $23.2 million during 2018, which is primarily attributable to losses in Switzerland. On December 22, 2017, the Tax Cuts and Jobs Act ("the Act") was enacted in the United States. The Act reduces the U.S. federal corporate tax rate from 35% to 21%, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (“SAB 118”), which allows the recording of provisional amounts during a measurement period not to extend beyond one year of the enactment date. As of December 31, 2018, the Company had available non-U.S. net operating loss carryforwards of $541.1 million which begin to expire in 2020. As of December 31, 2018, the Company has U.S. domestic federal research and development credit carryforwards of $1.9 million which expire in 2038 for federal purposes, which are net of uncertain tax positions of $0.9 million. As of December 31, 2018, the Company has U.S. domestic state research and development credit carryforwards of $1.8 million which begin to expire in 2033, which are net of uncertain tax positions of $0.7 million. ASC 740 clarifies the accounting for uncertainty in income taxes recognized in an enterprise’s financial statement by prescribing the minimum recognition threshold and measurement of a tax position taken or expected to be taken in a tax return. As of December 31, 2018, the Company had gross unrecognized tax benefits of $1.6 million of which $1.5 million would favorably impact the effective tax rate if recognized. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2018, 2017 and 2016, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s consolidated statements of operations and comprehensive loss. The aggregate changes in gross unrecognized tax benefits was as follows (in thousands): Years Ended December 31, 2018 2017 2016 Balance at beginning of year $ 354 $ 163 $ 49 Increases for tax positions taken during current period 1,212 178 134 Increases for tax positions taken in prior periods 29 13 — Decreases for tax positions taken during current period — — — Decreases for tax positions taken in prior periods — — (20 ) Balance at end of year $ 1,595 $ 354 $ 163 The Company files income tax returns in the U.S. federal jurisdiction, Massachusetts, and certain non-U.S. jurisdictions. The Company is subject to U.S. federal, Massachusetts, and non-U.S. income tax examinations by authorities for all tax years.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	14. Selected Quarterly Financial Data (Unaudited) The following table sets forth the Company’s quarterly financial data for the two years ended December 31, 2018. 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue $ 1,358 $ 1,088 $ 563 $ 115 Total operating expenses 28,355 38,374 49,995 $ 45,343 Loss from operations (26,997 ) (37,286 ) (49,432 ) $ (45,228 ) Net loss (28,300 ) (38,380 ) (50,711 ) $ (47,590 ) Net loss attributable to common shareholders (28,300 ) (38,380 ) (50,711 ) $ (47,590 ) Net loss per share attributable to common shareholders: Basic $ (0.62 ) $ (0.82 ) (1.07 ) $ (0.92 ) Diluted $ (0.62 ) $ (0.82 ) $ (1.07 ) $ (0.92 ) Weighted-average common shares outstanding used in net loss per share attributable to common shareholders: Basic 45,877,428 46,842,316 47,391,988 51,688,383 Diluted 45,877,428 46,842,316 47,391,988 51,688,383 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue $ 2,703 $ 3,582 $ 2,387 $ 32,325 Total operating expenses 23,447 24,888 25,957 $ 31,353 (Loss) income from operations (20,744 ) (21,306 ) (23,570 ) $ 972 Net (loss) income (21,475 ) (22,315 ) (24,707 ) $ 140 Net (loss) income attributable to common shareholders (21,475 ) (22,315 ) (24,707 ) $ 140 Net (loss) income per share attributable to common shareholders: Basic $ (0.54 ) $ (0.56 ) $ (0.62 ) $ 0.00 Diluted $ (0.54 ) $ (0.56 ) $ (0.62 ) $ 0.00 Weighted-average common shares outstanding used in net (loss) income per share attributable to common shareholders: Basic 39,725,947 39,895,938 40,088,718 40,509,897 Diluted 39,725,947 39,895,938 40,088,718 41,635,843

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	15. Related Party Transactions Casebia During the years ended December 31, 2018, 2017 and 2016 the Company recognized revenue of $2.5 million, $4.8 million and $1.2 million, respectively, related to the collaboration with Casebia. During the years ended December 31, 2018, 2017 and 2016 the Company recognized research and development expense of $3.8 million, $4.5 million and $1.7 million, respectively, related to the performance of services for Casebia. The Company and Casebia have engaged several research institutions and companies to identify new delivery strategies and applications of the gene-editing technology. Additionally, the Company and Casebia are also a party to a number of research license agreements. The Company and Casebia will share costs associated with the research and license agreements. Under both research and license agreements, the Company received reimbursements of $0.9 million, $4.4 million during 2018 and 2017, respectively. There were no reimbursements recorded during 2016. The reimbursements were recorded as a reduction of R&D expense in the income statement. Vertex In 2018, upon becoming owners of record of more than 10% of the voting interest of the Company, Vertex became a related party under ASC 850, Related party disclosures.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies and Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of (i) the Company, (ii) its wholly-owned subsidiaries, CRISPR Therapeutics Ltd., CRISPR Therapeutics Inc., CTX Financing GmbH, and TRACR Hematology Ltd., as of December 31, 2018. All intercompany accounts and transactions have been eliminated. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). Investments in partnerships where the Company has significant influence because it has a voting interest of 20% to 50%, are accounted for under the equity method. Results of associated companies are presented on a one-line basis. The Company accounts for its 50% investment share of Casebia Therapeutics LLP (“Casebia”) under the equity method of accounting. See Note 9 for further details. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, equity-based compensation expense, revenue recognition, equity method investments, and reported amounts of expenses during the reported period. Significant estimates in these consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses, valuation of equity method of investment, equity-based compensation expense, fair value of Common Shares, and the provision for or benefit from income taxes. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company and the Company’s chief operating decision maker, namely, the chief executive officer, view the Company’s operations and manage its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology.
Foreign Currency Translation and Transactions	Foreign Currency Translation and Transactions The Company’s reporting currency is the U.S. Dollar. The Company‘s consolidated entities have the U.S. dollar as their functional currency with the exception of CRISPR Ltd. which has the British Pound Sterling (“GBP”) as its functional currency. CRISPR Ltd. has assets and liabilities translated into U.S. dollars at exchange rates in effect at the end of the year. Revenue and expenses are translated using the average exchange rates for the period. Net unrealized gains and losses resulting from foreign currency translation are included in accumulated other comprehensive loss, which is a separate component of shareholders’ equity. Net foreign currency exchange transaction gains and losses resulting from the remeasurement of transactions denominated in currencies other than functional currency are included in other (expense) income, net in the consolidated statements of operations and comprehensive loss.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with maturities of 90 days or less from the purchase date to be cash equivalents. As of December 31, 2018 and 2017, the Company had $456.6 million and $239.8 million in cash equivalents, respectively. The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents.
Restricted Cash	Restricted Cash In 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230) Restricted Cash As of December 31, 2018 2017 2016 Cash and cash equivalents 456,649 239,758 315,520 Restricted Cash 3,163 3,154 3,150 Total $ 459,812 $ 242,912 $ 318,670
Accounts Receivable	Accounts Receivable Accounts receivable of $0.1 million and $2.6 million at December 31, 2018 and 2017, respectively, consist of receivables from Vertex Pharmaceuticals, Incorporated (“Vertex”) and Casebia. These amounts represent the balance due from the respective parties for the portion of our arrangements accounted for under ASC 606, Revenue from contracts with customers.
Other Receivables	Other Receivables Other receivables of $3.4 million and $1.9 million at December 31, 2018 and 2017, respectively, consists of receivables from Vertex and are included with prepaid and other expense in the consolidated balance sheet. These amounts represent the balance due from the portion of our arrangement accounted for under ASC 808, Collaborative Arrangements
Concentrations of Credit Risk and Off-balance Sheet Risk	Concentrations of Credit Risk and Off-balance Sheet Risk Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash. The Company’s cash is held in accounts with financial institutions that management believes are creditworthy. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial instruments consist of accounts payable, accrued expenses and other non-current liabilities. The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic 820, Fair Value Measurement and Disclosures The accounting standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value, which are the following: Level 1 — Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities. Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying amount of accounts receivable, other receivables, accounts payable, and accrued expenses as reported on the consolidated balance sheets as of December 31, 2018 and 2017, approximate fair value, due to the short-term duration of these instruments. The fair value of the Company’s equity method investment in Casebia was determined using level 3 inputs (See Note 9).
Property and Equipment	Property and Equipment Property and equipment is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Computer equipment 3 years Furniture, fixtures, and other 5 years Laboratory equipment 5 years Leasehold improvements Shorter of useful life or remaining lease term
Impairment of Long-lived Assets	Impairment of Long-lived Assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book value of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value. The Company has not recognized any impairment losses in the years ended December 31, 2018, 2017, and 2016.
Revenue Recognition	Revenue Recognition In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which supersedes existing revenue recognition guidance. The Company adopted ASU 2014-09 and its related amendments (collectively known as “ASC 606”) on January 1, 2018 using the modified retrospective method, by recognizing the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of equity at January 1, 2018. The reported results for 2018 reflect the application of ASC 606 guidance while the reported results for 2017 and prior were prepared under the guidance of ASC 605, Revenue Recognition (“ASC 605”). The Company has elected a practical expedient and applied ASC 606 only to contracts that are not completed at the date of initial application. ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. The Company’s revenue is from collaboration agreements. Within collaboration agreements, a counterparty may be a collaborator or partner that shares in the risks and benefits of developing a product to be marketed. These arrangements generally are in the scope of ASC 808, Collaborative Arrangements (“ASC 808”) yet may also contain vendor-customer aspects. Therefore, the Company considers all of the facts and circumstances to determine which transactions have a vendor-customer relationship that is subject to ASC 606. At the inception of each agreement the Company must determine which promised goods and services are under the scope of ASC 606 versus ASC 808 (discussed in the Collaborative Arrangements note below). In accordance with ASC 606, revenue is recognized when a customer obtains control of promised goods or services. The amount of revenue recognized reflects the consideration to which the Company expects to be entitled to receive in exchange for these goods and services. To achieve this core principle, the Company applies the following five steps: 1) Identify the contract with the customer A contract with a customer exists when (i) the Company enters into an enforceable contract with a customer that defines each party’s rights regarding the goods or services to be transferred and identifies the related payment terms, (ii) the contract has commercial substance, and (iii) the Company determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration. 2) Identify the performance obligations in the contract Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the good or service either on its own or together with other available resources, and are distinct in the context of the contract, whereby the transfer of the good or service is separately identifiable from other promises in the contract. To the extent a contract includes multiple promised goods and services, the Company must apply judgment to determine whether promised goods and services are capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation. 3) Determine the transaction price The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes. Determining the transaction price requires significant judgment, which is discussed in further detail for each of the Company’s contracts with customers in Note 9. 4) Allocate the transaction price to performance obligations in the contract If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. 5) Recognize revenue when or as the Company satisfies a performance obligation The Company satisfies performance obligations either over time or at a point in time. Revenue is recognized over time if either 1) the customer simultaneously receives and consumes the benefits provided by the entity’s performance, 2) the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced, or 3) the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer. Examples of control are using the asset to produce goods or services, enhance the value of other assets, settle liabilities, and holding or selling the asset. ASC 606 requires the Company to select a single revenue recognition method for the performance obligation that faithfully depicts the Company’s performance in transferring control of the goods and services. The guidance allows entities to choose between two methods to measure progress toward complete satisfaction of a performance obligation: 1. Output methods - recognize revenue on the basis of direct measurements of the value to the customer of the goods or services transferred to date relative to the remaining goods or services promised under the contract (e.g. surveys of performance completed to date, appraisals of results achieved, milestones reached, time elapsed, and units of produced or units delivered); and 2. Input methods - recognize revenue on the basis of the entity’s efforts or inputs to the satisfaction of a performance obligation (e.g., resources consumed, labor hours expended, costs incurred, or time elapsed) relative to the total expected inputs to the satisfaction of that performance obligation. The Company has the right to consideration from a customer in an amount that corresponds directly with the value to the customer of the entity’s performance completed to date (i.e. R&D services), as such the Company has elected a practical expedient to recognize revenue in the amount to which the entity has a right to invoice for such services. The terms of the Company’s collaboration and license agreements contain multiple promised goods and services, which include options to license CRISPR/Cas9-based therapeutic products directed to specific targets, referred to as co-exclusive or exclusive licenses, joint steering committee participation, as well as research and development activities to be performed by the Company on behalf of the collaboration partner related to the licensed targets. Payments that the Company may receive under these agreements include nonrefundable upfront fees, payments for research activities, payments based upon the achievement of specified milestones and royalties on any resulting net product sales. To date, the Company’s only source of revenue has been the collaboration and license and joint development and commercialization agreement with Vertex as well as research and development services provided to Casebia under the joint venture with Bayer HealthCare LLC (“Bayer”). Please refer to Note 9 for the specific accounting treatment and revenue recognized during the period for each of these arrangements. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company must consider the nature of the intellectual property to which the customer will have rights (i.e. access at a point in time or benefit of intellectual property enhancements over time). The Company recognizes revenue from non-refundable, up-front fees allocated to the license at a point in time/over the period the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone payments: At the inception of each arrangement that includes development, regulatory or commercial milestone payments for promised goods and services, the Company evaluates the circumstances of whether the milestones will be reached and estimates the amount to be included in the transaction price that will not cause a significant revenue reversal. The Company will evaluate these types of payments for customer options once those options have been exercised. ASC 606 suggests two alternatives to use when estimating the amount of variable consideration: the expected value method and the most likely amount method. Under the expected value method, an entity considers the sum of probability-weighted amounts in a range of possible consideration amounts. Under the most likely amount method, an entity considers the single most likely amount in a range of possible consideration amounts. The Company will use the most likely amount method for development and regulatory milestone payments. Management believes the most likely amount method is the better predictor as the Company expects to be entitled to only one of two possible amounts. Additionally, management believes that the most likely amount of milestone consideration is its stated amount. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. The transaction price is then allocated to performance obligations on a specific basis or on a relative stand-alone selling price basis. The Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates whether it is probable that a significant revenue reversal will not occur in future periods, and if necessary, adjusts its estimates of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). Up-front payments and fees are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Contract Balances The Company recognizes a contract asset when the Company transfers goods or services to a customer before the customer pays consideration or before payment is due, excluding any amounts presented as a receivable (i.e. accounts receivable). A contract asset is an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer. The contract liabilities (i.e. deferred revenue) primarily relate to contracts where we have received payment but we have not yet satisfied the related performance obligations. The advance consideration received from customers for R&D services or licenses bundled with other promises is a contract liability, recorded as deferred revenue, until the underlying performance obligations are transferred to the customer. The change in deferred revenue from December 31, 2017 to December 31, 2018 is primarily related to the transition adjustment upon the adoption of ASC 606. Income Taxes The adoption of ASC 606 resulted in a reduction of cumulative revenue as of January 1, 2018, which in turn generated additional deferred tax assets. As the Company fully reserves its net deferred tax assets in the jurisdictions impacted by the adoption of ASC 606, this impact was offset by a corresponding change to the valuation allowance. Impact of Adopting ASC 606 on the Financial Statements The Company adopted ASC 606 using the modified retrospective method. The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018 was recorded as an adjustment to accumulated deficit as of the adoption date. The Company elected to apply a practical expedient to reflect the aggregate effect of all modifications that occur before the beginning of the earliest period presented when identifying the satisfied and unsatisfied performance obligations, determining the transaction price, and allocating the transaction price to the satisfied and unsatisfied performance obligations. As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made to the consolidated balance sheet as of January 1, 2018: As Reported December 31, 2017 ASC 606 Adjustment Adjusted January 1, 2018 Consolidated Balance Sheet Data (in thousands): Other current liabilities $ 137 $ 102 $ 239 Total current liabilities $ 14,511 $ 102 $ 14,613 Deferred revenue $ 56,928 $ 1,046 $ 57,974 Total liabilities $ 83,514 $ 1,148 $ 84,662 Accumulated deficit $ (125,440 ) $ (1,148 ) $ (126,588 ) Total shareholders' equity $ 187,832 $ (1,148 ) $ 186,684 Total liabilities and shareholders’ equity $ 271,346 $ — $ 271,346 Impact of New Revenue Guidance on Financial Statement Line Items The following table compares the reported condensed consolidated balance sheet, statement of operations and cash flows, as of and for the year ended December 31, 2018, to the pro-forma amounts had the previous guidance been in effect: As of December 31, 2018 As Reported Under ASC 606 Adjustments Notes Adjusted Balance Under ASC 605 Consolidated Balance Sheet Data (in thousands): Other current liabilities $ 221 $ (102 ) (5) $ 119 Total current liabilities $ 27,746 $ (102 ) (5) $ 27,644 Deferred revenue $ 57,780 $ (750 ) (1)(2)(3)(5) $ 57,030 Total liabilities $ 96,821 $ (852 ) (1)(2)(3)(5) $ 95,969 Accumulated deficit $ (291,569 ) $ 852 (1)(2)(3) $ (290,717 ) Total shareholders' equity $ 392,195 $ 852 (1)(2)(3) $ 393,047 Total liabilities and shareholders’ equity $ 489,016 $ — (1)(2)(3) $ 489,016 Year Ended December 31, 2018 Consolidated Statement of Operations Data (in thousands): As Reported Under ASC 606 Adjustments Notes Adjusted Balance Under ASC 605 Collaboration revenue $ 3,124 $ (296 ) (2)(3) $ 2,828 Loss from operations $ (158,943 ) $ (296 ) (2)(3) $ (159,239 ) Net loss before income taxes $ (164,428 ) $ (296 ) (2)(3) $ (164,724 ) Net loss $ (164,981 ) $ (296 ) (2)(3) $ (165,277 ) Comprehensive loss $ (165,003 ) $ (296 ) (2)(3) $ (165,299 ) Consolidated Statement of Cash Flows (in thousands): Operating activities: Net loss $ (164,981 ) $ (296 ) (2)(3) $ (165,277 ) Reconciliation of net loss to net cash and restricted cash used in operating activities: Changes in: Deferred revenue $ (296 ) $ 398 (1)(2)(3)(4)(5) $ 102 Other liabilities, net $ 249 $ (102 ) (1)(2)(3)(4)(5) $ 147 Net cash and restricted cash (used in) operating activities $ (96,239 ) $ — $ (96,239 ) Increase (decrease) in cash and restricted cash $ 216,900 $ — $ 216,900 Cash and restricted cash, end of period $ 459,812 $ — $ 459,812 (1) Adjustment of $1,148 to reverse the ASC 606 transition adjustment from accumulated deficit and deferred revenue. (2) Adjustment of $194 for the year ended December 31, 2018, related to R&D services that would be deferred under ASC 605 versus recognized as invoiced under ASC 606. (3) Adjustment of $102 for the year ended December 31, 2018, related to non-exclusive research license revenue that would be recognized upon option exercise under ASC 605 versus recognized overtime under ASC 606. (4) Adjustment to reverse the ASC 606 transition adjustment to accumulated deficit and deferred revenue netted to zero as the transaction did not impact cash. (5) Adjustment to reclassify $102 from deferred revenue to other current liabilities (current deferred revenue) related to the change in revenue allocated to the non-exclusive research license recognized upon option exercise under ASC 605 versus ratably over time under ASC 606.
Collaboration Arrangements	Collaboration Arrangements The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC 808. Accordingly, the elements of the collaboration agreements that represent activities in which both parties are active participants and to which both parties are exposed to the significant risks and rewards that are dependent on the commercial success of the activities, are recorded as collaborative arrangements. The Company considers the guidance in ASC 606 in determining the appropriate treatment for the transactions between the Company and its collaborative partner and the transactions between the Company and third parties. Generally, the classification of transactions under the collaborative arrangements is determined based on the nature and contractual terms of the arrangement along with the nature of the operations of the participants. The Company evaluates the proper presentation of the commercial activities and the profit and loss sharing associated with the collaboration agreements. ASC 808 states that when payments between parties in a collaborative arrangement are not within the scope of other authoritative accounting literature, the income statement classification should be based on the nature of the arrangement, the nature of its business operations and the contractual terms of the arrangement. To the extent that these payments are not within the scope of other authoritative accounting literature, the income statement classification for the payments shall be based on an analogy to authoritative accounting literature or if there is no appropriate analogy, a reasonable, rational, and consistently applied accounting policy election.
Research and Development Expenses	Research and Development Expenses Research and development costs, which include employee compensation costs, facilities, lab supplies and materials, overhead, preclinical development, and other related costs, are charged to expense as incurred. Research and development costs also include the costs the Company incurs in its performance of services or provision of materials in connection with the funded research undertaken as a part of the Company’s collaborative agreement with Vertex and Casebia. See Note 9 for further details.
Operating Leases	Operating Leases The Company leases office and laboratory facilities under a non-cancelable operating lease agreements. The lease agreements contain free or escalating rent payment provisions. The Company recognizes rent expense under such leases on a straight-line basis over the term of the lease with the difference between the expense and the payments recorded as deferred rent on the consolidated balance sheets. Lease renewal periods are considered on a lease-by-lease basis in determining the lease term. Funding of leasehold improvements by the Company’s landlord are accounted for as a tenant improvement allowance and are amortized as a reduction of rent expense over the term of the lease. Leasehold improvements are amortized straight-line over the shorter of the useful life or the remaining lease term.
Equity-Based Compensation Expense	Equity Based Compensation Expense The Company recognizes equity-based compensation expense for awards of equity instruments to employees and non-employee directors based on the grant date fair value of those awards in accordance with FASB ASC Topic 718, Stock Compensation (“ASC 718”). ASC 718 requires all equity-based compensation awards to employees and non-employee directors, including grants of restricted shares and stock options, to be recognized as expense in the statements of operations based on their grant date fair values. The Company estimates the fair value of stock options using the Black-Scholes option pricing model. The Company uses the fair value of our Common Shares to determine the fair value of restricted share awards. Prior to July 1, 2018, the Company accounted for stock options issued to non-employees and employees of Casebia under FASB ASC Topic 505-50, Equity Based Payments to Non-Employees (“ASC 505-50”) through June 30, 2018. As such, the value of such options were periodically remeasured, and income or expense was recognized over their vesting terms. Compensation cost related to awards with service-based vesting schedules was recognized using the straight-line method. As of July 1, 2018, the Company adopted the FASB ASU No. 2018-07, Stock Compensation (“ASU 2018-07”) which provides improvements to nonemployee share-based payment accounting. ASU 2018-07 is intended to reduce the cost and complexity and to improve financial reporting for nonemployee share-based payments. The scope of ASC 718, which currently only includes share-based payments to employees was expanded to include share-based payments issued to nonemployees for goods or services. ASC 505-50, was superseded and consequently, the accounting for share-based payments to nonemployees and employees will be substantially aligned. As a result of adopting this standard, the fair value of outstanding nonemployee awards post adoption are no longer remeasured each reporting period and expense related to these awards was recorded based on the fair value measured as of June 30, 2018, the last period prior to the adoption of ASU 2018-07. The Black-Scholes option pricing model requires the input of certain subjective assumptions, including (i) the expected share price volatility, (ii) the calculation of expected term of the award, (iii) the risk-free interest rate and (iv) the expected dividend yield. Due to the lack of a public market for the trading of the Company’s Common Shares prior to its IPO and a lack of company-specific historical and implied volatility data, the Company based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The group of representative companies have characteristics similar to the Company, including stage of product development and focus on the life science industry. The Company uses the simplified method, which is the average of the final vesting tranche date and the contractual term, to calculate the expected term for options granted to employees as the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. For options granted to non-employees the Company utilizes the contractual term of the arrangement as the basis for the expected term assumption. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The Company assumed a dividend yield of zero as we have never paid dividends and has no current plans to pay any dividends on its Common Shares. The Company expenses the fair value of its equity-based compensation awards granted to employees and non-employees with only service-based vesting on a straight-line basis over the associated service period, which is generally the period in which the related services are received. The Company records the expense for equity-based compensation awards subject to performance-based milestone vesting over the remaining service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the expected satisfaction of the performance conditions as of the reporting date. The Company records expense for equity-based compensation awards subject to performance-based vesting conditions using the accelerated attribution method. The Company uses a Monte Carlo simulation option-pricing model to determine the fair value of market-based awards. The model uses the same input assumptions as the Black-Scholes model, yet, it also incorporates the possibility that the market condition may not be satisfied. Compensation cost related market-based awards are recognized regardless of whether the market condition is satisfied, provided that the requisite service has been provided.
Patent Costs	Patent Costs Costs to secure and prosecute patent application and other legal costs related to the protection of the Company’s intellectual property are expensed as incurred and are classified as general and administrative expenses in the Company’s consolidated statements of operations.
Income Taxes	Income Taxes Income taxes are recorded in accordance with FASB ASC Topic 740, Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2018 and 2017, the Company does not have any significant uncertain tax positions. The Company’s practice is to recognize interest and/or penalties related to income tax matters in income tax expense. See Note 14 for further details.
Comprehensive Loss	Comprehensive Loss Comprehensive loss consists of net income or loss and changes in equity during the period from transactions and other events and circumstances generated from non-owner sources. The Company’s net loss equals comprehensive loss, net of any changes in the foreign currency translation adjustment, for all periods presented. In addition, comprehensive loss attributable to the noncontrolling interest equals net loss for all periods presented.
Variable Interest Entities	Variable Interest Entities The Company reviews each legal entity formed by parties related to the Company to determine whether or not the Company has a variable interest in the entity and whether or not the entity would meet the definition of a VIE in accordance with FASB ASC Topic 810, Consolidation If the Company determines it is the primary beneficiary of a VIE that meets the definition of a business, the Company measures the assets, liabilities and noncontrolling interests of the newly consolidated entity at fair value in accordance with FASB ASC Topic 805, Business Combinations In February 2016, Casebia Therapeutics LLP, a limited liability partnership, was formed in the United Kingdom. In March 2016 upon consummation of the JV, Bayer and the Company each received a 50% equity interest in the entity in exchange for their contributions to the entity. The Company determined that Casebia was considered a VIE and concluded that it is not the primary beneficiary of the VIE. As such, the Company did not consolidate Casebia’s results into the consolidated financial statements. See Note 4 for further details.
Net Loss Per Share Attributable to Common Shareholders	Net Loss Per Share Attributable to Common Shareholders Basic net income (loss) per share is calculated by dividing net income (loss) attributable to common shareholders by the weighted-average number of common shares outstanding during the period. Diluted net income per share is calculated by dividing the net income attributable to common shareholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from outstanding stock options and warrants using the treasury stock method. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in common stock equivalent shares): As of December 31, 2018 2017 2016 Outstanding options 6,689,311 6,262,339 4,535,371 Unvested unissued restricted shares 327,342 157,515 89,367 Total 7,016,653 6,419,854 4,624,738
Subsequent Events	Subsequent Events The Company considered the events or transactions occurring after the balance sheet date, but prior to the issuance of the consolidated financial statements, for potential recognition or disclosure in its consolidated financial statements. All significant subsequent events have been properly disclosed in the consolidated financial statements.
New Accounting Pronouncements - Recently Adopted	New Accounting Pronouncements – Recently Adopted Revenue Recognition As described above, the Company adopted ASC 606 on January 1, 2018 using the modified retrospective method, by recognizing the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of equity at January 1, 2018. The reported results for 2018 reflect the application of ASC 606 guidance while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition (“ASC 605”). The Company has elected a practical expedient and applied ASC 606 only to contracts that are not completed at the date of initial application In November 2018, The FASB amended ASC 808 and ASC 606 to clarify that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. The guidance 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 guidance amends ASC 808 to refer to the unit-of-account guidance in ASC 606 and requires it to be used only when assessing whether a transaction is in the scope of ASC 606. The Company early adopted the guidance in Q4 2018. The adoption of this guidance did not have a material impact on the Company’s financial position and results of operations. Financial Instrument Accounting In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities (“ASU 2016-01”). The new standard amends certain aspects of accounting and disclosure requirements of financial instruments, including the requirement that equity investments with readily determinable fair values be measured at fair value with changes in fair value recognized in the results of operations. The new standard was effective January 1, 2018. The Company adopted ASU 2016-01 in the first quarter of 2018. The adoption of this guidance did not have a material impact on the Company's financial position and results of operations. Statement of Cash Flows As discussed above, the Company adopted ASU 2016-18 retrospectively in the first quarter of 2018 and the change in accounting principle is reflected in the statements of cash flows years ended December 31, 2018, 2017 and 2016 accordingly. The adoption of this guidance did not have a material impact on the Company's financial position and results of operations. Business Combinations In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805) (“ASU 2017-01”). ASU 2017-01 clarifies whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The purpose of the guidance is to narrow the definition of a business at it relates to recording transactions as business acquisitions or asset acquisitions. The Company adopted ASU No. 2017-01 in the first quarter of 2018. The adoption of this guidance did not have a material impact on the Company's financial position and results of operations. Stock Compensation In May 2017, the FASB issued ASU 2017-09, Compensation – Stock Compensation (“ASU 2017-09”): Scope Modification Accounting. The new standard is intended to reduce the diversity in practice and cost and complexity when applying the guidance in Topic 718 to a change to the terms or conditions of a share-based payment award. The Company adopted ASU No. 2017-09 in the first quarter of 2018. The adoption of this guidance did not have a material impact on the Company's financial position and results of operations. As described above, the Company early adopted ASU 2018-07 on a prospective basis on July 1, 2018. As a result of adopting this standard, the fair value of outstanding nonemployee awards as of June 30, 2018 will no longer be remeasured each reporting period. All future expense related to these awards will be recorded based on the fair value measured as of June 30, 2018, the last period prior to the adoption of ASU 2018-07. The adoption of this guidance did not have a material impact of the Company’s consolidated financial statements.
New Accounting Pronouncements - to be adopted in future periods	New Accounting Pronouncements – To Be Adopted In Future Periods Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which applies to all leases and will require lessees to record most leases on the balance sheet but recognize expense in a manner similar to the current standard. In July 2018, the FASB also issued ASU No. 2018-11, Codification Improvements to Topic 842, Leases (“ASU 2018-11”), which clarifies and corrects narrow aspects of the guidance issued in ASU 2016-02 (collectively “ASC 842”). On January 1, 2019, we adopted ASC 842 using the modified-retrospective approach. The Company has reviewed its portfolio of existing leases and current accounting policies to identify and assess the potential differences that would result from applying the requirements of the new standard. The amended guidance will result in the recognition of additional right of use assets and corresponding liabilities on its condensed consolidated balance sheets. The new standard does not have a material impact on the Company’s consolidated statement of operations or cash flows. The Company has implemented appropriate changes to its controls to support lease accounting and related disclosures under the new standard. The Company has elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed us to carry forward the historical lease classification.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Basis of Presentation (Tables)	12 Months Ended
	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Schedule of Cash, Cash Equivalents and Restricted Cash	Cash, cash equivalents and restricted cash at the end of each period presented in the Company’s consolidated statements of cash flows consisted of the following: As of December 31, 2018 2017 2016 Cash and cash equivalents 456,649 239,758 315,520 Restricted Cash 3,163 3,154 3,150 Total $ 459,812 $ 242,912 $ 318,670
Schedule of Estimated Useful Lives of Assets	Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Computer equipment 3 years Furniture, fixtures, and other 5 years Laboratory equipment 5 years Leasehold improvements Shorter of useful life or remaining lease term
Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share	The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in common stock equivalent shares): As of December 31, 2018 2017 2016 Outstanding options 6,689,311 6,262,339 4,535,371 Unvested unissued restricted shares 327,342 157,515 89,367 Total 7,016,653 6,419,854 4,624,738
ASU 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Modified Retrospective Method to Adopt New Revenue Guidance and Adjustments to Consolidated Balance Sheet	As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made to the consolidated balance sheet as of January 1, 2018: As Reported December 31, 2017 ASC 606 Adjustment Adjusted January 1, 2018 Consolidated Balance Sheet Data (in thousands): Other current liabilities $ 137 $ 102 $ 239 Total current liabilities $ 14,511 $ 102 $ 14,613 Deferred revenue $ 56,928 $ 1,046 $ 57,974 Total liabilities $ 83,514 $ 1,148 $ 84,662 Accumulated deficit $ (125,440 ) $ (1,148 ) $ (126,588 ) Total shareholders' equity $ 187,832 $ (1,148 ) $ 186,684 Total liabilities and shareholders’ equity $ 271,346 $ — $ 271,346
Impact of New Revenue Guidance on Financial Statement Line Items	The following table compares the reported condensed consolidated balance sheet, statement of operations and cash flows, as of and for the year ended December 31, 2018, to the pro-forma amounts had the previous guidance been in effect: As of December 31, 2018 As Reported Under ASC 606 Adjustments Notes Adjusted Balance Under ASC 605 Consolidated Balance Sheet Data (in thousands): Other current liabilities $ 221 $ (102 ) (5) $ 119 Total current liabilities $ 27,746 $ (102 ) (5) $ 27,644 Deferred revenue $ 57,780 $ (750 ) (1)(2)(3)(5) $ 57,030 Total liabilities $ 96,821 $ (852 ) (1)(2)(3)(5) $ 95,969 Accumulated deficit $ (291,569 ) $ 852 (1)(2)(3) $ (290,717 ) Total shareholders' equity $ 392,195 $ 852 (1)(2)(3) $ 393,047 Total liabilities and shareholders’ equity $ 489,016 $ — (1)(2)(3) $ 489,016 Year Ended December 31, 2018 Consolidated Statement of Operations Data (in thousands): As Reported Under ASC 606 Adjustments Notes Adjusted Balance Under ASC 605 Collaboration revenue $ 3,124 $ (296 ) (2)(3) $ 2,828 Loss from operations $ (158,943 ) $ (296 ) (2)(3) $ (159,239 ) Net loss before income taxes $ (164,428 ) $ (296 ) (2)(3) $ (164,724 ) Net loss $ (164,981 ) $ (296 ) (2)(3) $ (165,277 ) Comprehensive loss $ (165,003 ) $ (296 ) (2)(3) $ (165,299 ) Consolidated Statement of Cash Flows (in thousands): Operating activities: Net loss $ (164,981 ) $ (296 ) (2)(3) $ (165,277 ) Reconciliation of net loss to net cash and restricted cash used in operating activities: Changes in: Deferred revenue $ (296 ) $ 398 (1)(2)(3)(4)(5) $ 102 Other liabilities, net $ 249 $ (102 ) (1)(2)(3)(4)(5) $ 147 Net cash and restricted cash (used in) operating activities $ (96,239 ) $ — $ (96,239 ) Increase (decrease) in cash and restricted cash $ 216,900 $ — $ 216,900 Cash and restricted cash, end of period $ 459,812 $ — $ 459,812 (1) Adjustment of $1,148 to reverse the ASC 606 transition adjustment from accumulated deficit and deferred revenue. (2) Adjustment of $194 for the year ended December 31, 2018, related to R&D services that would be deferred under ASC 605 versus recognized as invoiced under ASC 606. (3) Adjustment of $102 for the year ended December 31, 2018, related to non-exclusive research license revenue that would be recognized upon option exercise under ASC 605 versus recognized overtime under ASC 606. (4) Adjustment to reverse the ASC 606 transition adjustment to accumulated deficit and deferred revenue netted to zero as the transaction did not impact cash. (5) Adjustment to reclassify $102 from deferred revenue to other current liabilities (current deferred revenue) related to the change in revenue allocated to the non-exclusive research license recognized upon option exercise under ASC 605 versus ratably over time under ASC 606.

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net, consists of the following (in thousands): As of December 31, 2018 2017 Computer equipment $ 443 $ 285 Furniture, fixtures, and other 2,453 2,104 Laboratory equipment 8,964 6,603 Leasehold improvements 13,776 13,776 Construction work in process 239 0 Total property and equipment, gross 25,875 22,768 Accumulated Depreciation (7,375 ) (3,911 ) Total property and equipment, net $ 18,500 $ 18,857

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets, Net of Accumulated Amortization	Intangible assets, net of accumulated amortization, are as follows (in thousands): Acquired intangible asset Cost Accumulated Amortization Net As of December 31, 2018 $ 547 $ (258 ) $ 289 As of December 31, 2017 $ 547 $ (203 ) $ 344
Schedule of Estimated Future Amortization of Acquired Intangible Assets	The estimated future amortization of acquired intangible assets as of December 31, 2018 is expected to be as follows (in thousands): For the Year Ended December 31, Amount 2019 55 2020 55 2021 55 2022 55 2023 55 Thereafter 14 Total amortization $ 289

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): As of December 31, 2018 2017 Payroll and employee-related costs $ 7,321 $ 5,550 Research costs $ 7,973 2,285 Licensing fees $ 625 609 Professional fees $ 1,848 2,176 Intellectual property costs $ 2,193 500 Accrued property and equipment $ 294 — Other $ 598 241 Total $ 20,852 $ 11,361

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Minimum Payments Required under Leases	Future minimum payments required under the leases as of December 31, 2018, are as follows (in thousands): Years Ended December 31, Amount 2019 $ 6,275 2020 6,866 2021 7,072 2022 5,874 2023 5,855 Thereafter 18,639 Total minimum lease payments $ 50,581

Equity-based Compensation (Tabl

Equity-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock-Based Compensation Expense	Stock-based compensation, measured at the grant date based on the fair value of the award, is typically recognized as expense ratably over the requisite service period . Stock-based compensation awards subject to performance-based vesting conditions are recognized over the requisite service period using the accelerated attribution method. The following table presents stock-based compensation expense in the Company’s Consolidated Statements of Operations: Years Ended December 31, 2018 2017 2016 Research and development $ 17,557 $ 8,800 $ 4,848 General and administrative $ 17,428 10,073 5,844 Loss from equity method investment $ 4,275 1,763 152 Total $ 39,260 $ 20,636 $ 10,844
Fair Value of Employee and Non-employee Stock Option Award on the Grant Date Using the Black-Scholes Option-Pricing Model	The Company estimated the fair value of each employee and non-employee stock option award on the grant date using the Black-Scholes option-pricing model based on the following assumptions: Years Ended December 31, 2018 2017 2016 Employees: Options granted 2,188,097 2,894,850 2,411,240 Weighted - average exercise price $ 51.82 $ 16.92 $ 12.19 Weighted-average grant date fair value $ 33.81 $ 10.86 $ 8.47 Assumptions: Weighted-average expected volatility 71.9 % 72.1 % 81.0 % Expected term (in years) 6.0 6.0 6.0 Weighted-average risk free interest rate 2.8 % 2.0 % 1.4 % Expected dividend yield 0.0 % 0.0 % 0.0 % Non employees: Options granted 21,500 104,997 215,710 Weighted- average exercise price $ 42.75 $ 18.74 $ 19.54 Weighted- average grant date fair value $ 34.74 $ 19.35 $ 17.38 Assumptions: Weighted average expected volatility 77.9 % 81.5 % 88.2 % Expected term (in years) 10.0 9.4 10.0 Weighted-average risk free interest rate 3.0 % 2.4 % 2.4 % Expected dividend yield 0.0 % 0.0 % 0.0 %
Summary of Stock Option Activity for Employees and Non-employees	The following table summarizes stock option activity for employees and non-employees during the year ended December 31, 2018 (intrinsic value in thousands): Stock Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2017 6,262,339 $ 13.24 8.8 $ 64,120 Granted 2,209,597 $ 51.73 Exercised (946,131 ) $ 10.95 Cancelled or forfeited (836,494 ) $ 20.11 Outstanding at December 31, 2018 6,689,311 $ 25.42 8.3 68,572 Exercisable at December 31, 2018 2,541,789 $ 15.74 7.7 $ 38,486 Vested or expected to vest at December 31, 2018 (1) 6,689,311 $ 25.42 8.3 $ 68,572 (1) This represents the number of vested stock options as of December 31, 2018 plus the unvested outstanding options at December 31, 2018 expected to vest in the future.
Summary of the Company's Restricted Stock Activity	The following table summarizes restricted stock activity for employees and non-employees during the year ended December 31, 2018: Reflected as outstanding upon vesting Reflected as outstanding upon grant date Total Weighted- Average Grant Date Fair Value Unvested restricted common shares at December 31, 2017 157,515 208,886 366,401 $ 8.49 Granted 251,500 — 251,500 $ 44.51 Vested (77,673 ) (168,613 ) (246,286 ) $ 7.58 Cancelled or forfeited (4,000 ) (40,273 ) (44,273 ) $ 8.51 Unvested restricted common shares at December 31, 2018 327,342 — 327,342 $ 36.72

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Loss Before Provision for Income Taxes	For the years ended December 31, 2018, 2017 and 2016, the loss before provision for income taxes consist of the following (in thousands): Years Ended December 31, 2018 2017 2016 Domestic $ 5,966 $ 5,184 $ 3,322 Foreign (170,394 ) (71,792 ) (26,040 ) Total $ (164,428 ) $ (66,608 ) $ (22,718 )
Schedule of (Provision for) Benefit from Income Taxes	The (provision for) benefit from income taxes consist of the following (in thousands): Years Ended December 31, 2018 2017 2016 Current income taxes: Federal $ (416 ) $ (1,533 ) $ (649 ) State (131 ) (42 ) 11 Foreign — 6 17 Total current income taxes (547 ) (1,569 ) (621 ) Deferred income taxes: Federal (6 ) (477 ) 30 State — 297 105 Foreign — — 2 Total deferred income taxes (6 ) (180 ) 137 Total income tax provision $ (553 ) $ (1,749 ) $ (484 )
Schedule of Reconciliation of Income Tax Expense Computed at Statutory Corporate Income Tax Rate to Effective Income Tax Rate	A reconciliation of income tax expense computed at the statutory corporate income tax rate to the effective income tax rate for the years ended December 31, 2018, 2017 and 2016 is as follows: Years Ended December 31, 2018 2017 2016 Income tax expense at statutory rate 9.3 % 9.3 % 10.3 % State income tax, net of federal benefit 0.7 % 0.3 % 1.3 % Nondeductible expenses 0.0 % 0.0 % 1.6 % Foreign rate differential (0.4 %) (2.5 %) (3.3 %) Statutory to US GAAP permanent differences 1.0 % 1.8 % 6.6 % Stock-based compensation 1.4 % (2.9 %) (4.9 %) Research credits 1.8 % 0.8 % 3.1 % Change in valuation allowance (14.1 %) (9.4 %) (16.8 %) Effective income tax rate (0.3 %) (2.6 %) (2.1 %)
Schedule of Significant Components of Company's Deferred Tax Assets	Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets are comprised of the following (in thousands): Years Ended December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 25,418 $ 9,987 Accruals and reserves 1,816 1,123 Deferred Rent 3,300 3,494 Other deferred tax assets 51 36 Stock based compensation 2,871 — Deferred revenue 3,264 1,721 Research credit 3,322 543 Total deferred tax assets 40,042 16,904 Less valuation allowance (36,208 ) (13,041 ) Net deferred tax assets 3,834 3,863 Deferred tax liabilities: Depreciation (3,785 ) (3,791 ) Intangible assets (49 ) (59 ) Other deferred tax liabilities (22 ) (31 ) Total deferred tax liabilities (3,856 ) (3,881 ) Long term deferred taxes $ (22 ) $ (18 )
Schedule of Aggregate Changes in Gross Unrecognized Tax Benefits	The aggregate changes in gross unrecognized tax benefits was as follows (in thousands): Years Ended December 31, 2018 2017 2016 Balance at beginning of year $ 354 $ 163 $ 49 Increases for tax positions taken during current period 1,212 178 134 Increases for tax positions taken in prior periods 29 13 — Decreases for tax positions taken during current period — — — Decreases for tax positions taken in prior periods — — (20 ) Balance at end of year $ 1,595 $ 354 $ 163

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data	The following table sets forth the Company’s quarterly financial data for the two years ended December 31, 2018. 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue $ 1,358 $ 1,088 $ 563 $ 115 Total operating expenses 28,355 38,374 49,995 $ 45,343 Loss from operations (26,997 ) (37,286 ) (49,432 ) $ (45,228 ) Net loss (28,300 ) (38,380 ) (50,711 ) $ (47,590 ) Net loss attributable to common shareholders (28,300 ) (38,380 ) (50,711 ) $ (47,590 ) Net loss per share attributable to common shareholders: Basic $ (0.62 ) $ (0.82 ) (1.07 ) $ (0.92 ) Diluted $ (0.62 ) $ (0.82 ) $ (1.07 ) $ (0.92 ) Weighted-average common shares outstanding used in net loss per share attributable to common shareholders: Basic 45,877,428 46,842,316 47,391,988 51,688,383 Diluted 45,877,428 46,842,316 47,391,988 51,688,383 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue $ 2,703 $ 3,582 $ 2,387 $ 32,325 Total operating expenses 23,447 24,888 25,957 $ 31,353 (Loss) income from operations (20,744 ) (21,306 ) (23,570 ) $ 972 Net (loss) income (21,475 ) (22,315 ) (24,707 ) $ 140 Net (loss) income attributable to common shareholders (21,475 ) (22,315 ) (24,707 ) $ 140 Net (loss) income per share attributable to common shareholders: Basic $ (0.54 ) $ (0.56 ) $ (0.62 ) $ 0.00 Diluted $ (0.54 ) $ (0.56 ) $ (0.62 ) $ 0.00 Weighted-average common shares outstanding used in net (loss) income per share attributable to common shareholders: Basic 39,725,947 39,895,938 40,088,718 40,509,897 Diluted 39,725,947 39,895,938 40,088,718 41,635,843

Organization and Operations - A

Organization and Operations - Additional Information (Detail) - USD ($)	1 Months Ended				12 Months Ended
	Sep. 30, 2018	Aug. 31, 2018	Jan. 31, 2018	Oct. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Organization and operations [Line Items]
Company formation date					Oct. 28, 2013
Company formation country name					Basel, Switzerland
Accumulated deficit					$ (291,569,000)	$ (125,440,000)
Proceeds from issuance of common shares				$ 35,000,000	307,053,000	0	$ 89,061,000
Cash					456,649,000	$ 239,758,000
Sales Agreement With Jefferies LLC [Member] | Maximum [Member]
Organization and operations [Line Items]
Aggregate estimated gross proceeds		$ 125,000,000
Equity Offering [Member]
Organization and operations [Line Items]
Issuance of common shares, net of issuance cost (in shares)	4,210,526		5,750,000
Common shares price per share	$ 47.50		$ 22.75
Proceeds from issuance of common shares	$ 187,600,000		$ 122,600,000
Stamp taxes on issuance proceeds					$ 3,100,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies and Basis of Presentation - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018USD ($)Segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Mar. 31, 2016	Feb. 12, 2016
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Cash equivalents	$ 456,600,000	$ 239,800,000
Accounts receivable	88,000	2,626,000
Impairment loss	$ 0	0	$ 0
Assumed dividend yield, percent	0.00%
Significant uncertain tax positions	$ 0	0	$ 0
Vertex and Casebia [Member]
Summary Of Significant Accounting Policies [Line Items]
Other receivables	3,400,000	1,900,000
Vertex and Casebia [Member] | Collaborative Arrangement [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable	100,000	$ 2,600,000
Allowance	$ 0
Casebia Therapeutics LLP [Member]
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	50.00%			50.00%	50.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies and Basis of Presentation - Schedule of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 456,649	$ 239,758	$ 315,520
Restricted Cash	3,163	3,154	3,150
Total	$ 459,812	$ 242,912	$ 318,670	$ 156,661

Summary of Significant Accoun_6

Summary of Significant Accounting Policies and Basis of Presentation - Schedule of Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2018
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	3 years
Furniture, Fixtures, and Other [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	5 years
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	5 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Leasehold improvements	Shorter of useful life or remaining lease term

Summary of Significant Accoun_7

Summary of Significant Accounting Policies and Basis of Presentation - Additional Information1 (Detail)	Dec. 31, 2018
Maximum [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Summary Of Significant Accounting Policies [Line Items]
Period between payment by the customer and the transfer of the promised goods or services	1 year

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Modified Retrospective Method to Adopt New Revenue Guidance and Adjustments to Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other current liabilities	$ 221		$ 137
Total current liabilities	27,746		14,511
Deferred revenue	57,780		56,928
Total liabilities	96,821		83,514
Accumulated deficit	(291,569)		(125,440)
Total shareholders' equity	392,195		187,832
Total liabilities and shareholders’ equity	489,016		$ 271,346
ASU 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other current liabilities		$ 239
Total current liabilities		14,613
Deferred revenue		57,974
Total liabilities		84,662
Accumulated deficit		(126,588)
Total shareholders' equity		186,684
Total liabilities and shareholders’ equity		271,346
ASC 606 Adjustment [Member] | ASU 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other current liabilities	(102)	102
Total current liabilities	(102)	102
Deferred revenue	(750)	1,046
Total liabilities	(852)	1,148
Accumulated deficit	852	(1,148)
Total shareholders' equity	$ 852	$ (1,148)

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Impact of New Revenue Guidance on Financial Statement Line Items (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016		Jan. 01, 2018	Dec. 31, 2015
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other current liabilities	$ 221				$ 137				$ 221		$ 137
Total current liabilities	27,746				14,511				27,746		14,511
Deferred revenue	57,780				56,928				57,780		56,928
Total liabilities	96,821				83,514				96,821		83,514
Accumulated deficit	(291,569)				(125,440)				(291,569)		(125,440)
Total shareholders' equity	392,195				187,832				392,195		187,832
Total liabilities and shareholders’ equity	489,016				271,346				489,016		271,346
Collaboration revenue	115	$ 563	$ 1,088	$ 1,358	32,325	$ 2,387	$ 3,582	$ 2,703	3,124	[1]	40,997	[1]	$ 5,164	[1]
Loss from operations	(45,228)	(49,432)	(37,286)	(26,997)	972	(23,570)	(21,306)	(20,744)	(158,943)		(64,648)		(68,130)
Net loss before income taxes									(164,428)		(66,608)		(22,718)
Net loss	(47,590)	(50,711)	(38,380)	(28,300)	140	(24,707)	(22,315)	(21,475)	(164,981)		(68,357)		(23,202)
Comprehensive loss									(165,003)		(68,317)		(23,220)
Operating activities:
Net loss	(47,590)	$ (50,711)	$ (38,380)	$ (28,300)	140	$ (24,707)	$ (22,315)	$ (21,475)	(164,981)		(68,357)		(23,202)
Changes in:
Deferred revenue									(296)		(20,718)		1,917
Other liabilities, net									249		270		(17)
Net cash and restricted cash (used in) operating activities									(96,239)		(70,093)		(52,860)
Increase (decrease) in cash and restricted cash									216,900		(75,758)		162,009
Cash and restricted cash, end of period	459,812				$ 242,912				459,812		$ 242,912		$ 318,670			$ 156,661
ASU 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other current liabilities															$ 239
Total current liabilities															14,613
Deferred revenue															57,974
Total liabilities															84,662
Accumulated deficit															(126,588)
Total shareholders' equity															186,684
Total liabilities and shareholders’ equity															271,346
Adjustments [Member] | ASU 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other current liabilities	(102)								(102)						102
Total current liabilities	(102)								(102)						102
Deferred revenue	(750)								(750)						1,046
Total liabilities	(852)								(852)						1,148
Accumulated deficit	852								852						(1,148)
Total shareholders' equity	852								852						$ (1,148)
Collaboration revenue									(296)
Loss from operations									(296)
Net loss before income taxes									(296)
Net loss									(296)
Comprehensive loss									(296)
Operating activities:
Net loss									(296)
Changes in:
Deferred revenue									398
Other liabilities, net									(102)
Adjusted Balance Under ASC 605 [Member] | ASU 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Other current liabilities	119								119
Total current liabilities	27,644								27,644
Deferred revenue	57,030								57,030
Total liabilities	95,969								95,969
Accumulated deficit	(290,717)								(290,717)
Total shareholders' equity	393,047								393,047
Total liabilities and shareholders’ equity	489,016								489,016
Collaboration revenue									2,828
Loss from operations									(159,239)
Net loss before income taxes									(164,724)
Net loss									(165,277)
Comprehensive loss									(165,299)
Operating activities:
Net loss									(165,277)
Changes in:
Deferred revenue									102
Other liabilities, net									147
Net cash and restricted cash (used in) operating activities									(96,239)
Increase (decrease) in cash and restricted cash									216,900
Cash and restricted cash, end of period	$ 459,812								$ 459,812
[1]	Including the following amounts of revenue from a related party, see Note 15:

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Impact of New Revenue Guidance on Financial Statement Line Items (Parenthetical) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accumulated deficit		$ (291,569)	$ (125,440)
Research and development	[1]	113,773	$ 69,800	$ 42,238
ASU 2014-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accumulated deficit					$ (126,588)
ASU 2014-09 [Member] | ASC 606 Adjustment [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred revenue					1,148
Accumulated deficit		852			$ (1,148)
Research and development		194
Non-exclusive research revenue		102
ASU 2014-09 [Member] | ASC 606 Adjustment [Member] | Other Current Liabilities [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred revenue current		$ 102
[1]	Including the following amounts of research and development from a related party, see Note 15:

Summary of Significant Accou_11

Summary of Significant Accounting Policies and Basis of Presentation - Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of net loss per share	7,016,653	6,419,854	4,624,738
Outstanding Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of net loss per share	6,689,311	6,262,339	4,535,371
Unvested Unissued Restricted Shares [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of net loss per share	327,342	157,515	89,367

Property and Equipment, net - S

Property and Equipment, net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 25,875	$ 22,768
Accumulated Depreciation	(7,375)	(3,911)
Total property and equipment, net	18,500	18,857
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	443	285
Furniture, Fixtures, and Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	2,453	2,104
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	8,964	6,603
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	13,776	13,776
Construction Work in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 239	$ 0

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Depreciation expense	$ 3.5	$ 3	$ 0.9

Variable Interest Entities - Ad

Variable Interest Entities - Additional Information (Detail) - Casebia Therapeutics LLP [Member]	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2016	Feb. 12, 2016
Variable Interest Entity [Line Items]
Date of formation of joint venture entity	Feb. 12, 2016
Equity method investment, ownership percentage	50.00%	50.00%	50.00%
Bayer Healthcare LLC [Member]
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage		50.00%

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - Intellectual Property Rights [Member] - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Estimated useful life	10 years
Amortization expenses	$ 100,000	$ 100,000	$ 100,000
Remaining amortization period	5 years 3 months 18 days
Impairment charges	$ 0	$ 0	$ 0

Intangible Assets - Schedule of

Intangible Assets - Schedule of Intangible Assets, Net of Accumulated Amortization (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Acquired intangible asset, Net	$ 289	$ 344
Intellectual Property Rights [Member]
Finite Lived Intangible Assets [Line Items]
Acquired intangible asset, Cost	547	547
Acquired intangible asset, Accumulated Amortization	(258)	(203)
Acquired intangible asset, Net	$ 289	$ 344

Intangible Assets - Schedule _2

Intangible Assets - Schedule of Estimated Future Amortization of Acquired Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Acquired intangible asset, Net	$ 289	$ 344
Intellectual Property Rights [Member]
Finite Lived Intangible Assets [Line Items]
2,019	55
2,020	55
2,021	55
2,022	55
2,023	55
Thereafter	14
Acquired intangible asset, Net	$ 289	$ 344

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities Current [Abstract]
Payroll and employee-related costs	$ 7,321	$ 5,550
Research costs	7,973	2,285
Licensing fees	625	609
Professional fees	1,848	2,176
Intellectual property costs	2,193	500
Accrued property and equipment	294
Other	598	241
Total	$ 20,852	$ 11,361

Convertible Loans - Additional

Convertible Loans - Additional Information (Detail) - USD ($)	Jan. 29, 2016	Dec. 19, 2015	Oct. 26, 2015	Dec. 31, 2015	Dec. 07, 2015	Dec. 31, 2016	Dec. 31, 2018
Debt Conversion [Line Items]
Aggregate net proceeds borrowed						$ 35,010,000
Conversion of convertible loans to Series B Preferred Shares						61,929,000
Gain on extinguishment of debt						$ 11,482,000
Vertex Convertible Loans [Member]
Debt Conversion [Line Items]
Borrowings under loan agreement			$ 40,000,000
Loan, accrued interest rate			2.50%
Loan agreement maturity date			Apr. 26, 2016
Aggregate net proceeds borrowed					$ 38,200,000
Conversion of convertible loans to Series B Preferred Shares	$ 200,000
Bayer Convertible Loans [Member]
Debt Conversion [Line Items]
Loan agreement maturity date				Jan. 29, 2016
Aggregate net proceeds borrowed	$ 35,000,000	$ 35,000,000
Preferred shares, conversion price per share		$ 13.43
Borrowings under loan agreement							$ 35,000,000
Loan, accrued interest rate							2.00%
Fair value of convertible loan							$ 24,500,000
Series B Redeemable Convertible Preferred Shares [Member]
Debt Conversion [Line Items]
Preferred shares, shares issued upon conversion	2,859,278
Preferred shares, conversion price per share	$ 9.33
Series B Redeemable Convertible Preferred Shares [Member] | Vertex Convertible Loans [Member]
Debt Conversion [Line Items]
Preferred shares, shares issued upon conversion	2,859,278
Preferred shares, conversion price per share	$ 13.43
Fair value of convertible loan	$ 26,900,000
Gain on extinguishment of debt	11,500,000
Series B Redeemable Convertible Preferred Shares [Member] | Bayer Convertible Loans [Member]
Debt Conversion [Line Items]
Conversion of convertible loans to Series B Preferred Shares	$ 35,000,000
Preferred shares, shares issued upon conversion	2,605,330
Preferred shares, conversion price per share	$ 13.43
Fair value of convertible loan	$ 24,500,000
Allocated to convertible loan	27,000,000
Interest expense	$ 8,000,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)		1 Months Ended		3 Months Ended	12 Months Ended
		Sep. 30, 2016	May 31, 2016	Dec. 31, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Contingencies And Commitments [Line Items]
Rental expense							$ 5,700,000	$ 6,900,000	$ 4,200,000
Research and development expense	[1]						113,773,000	69,800,000	42,238,000
Cost sharing expensed relating to patent maintenance, defense and prosecution, incurred							2,400,000	1,200,000	$ 2,800,000
Cost sharing expensed relating to patent maintenance, defense and prosecution, accrued							1,900,000	400,000
Manufacturing Agreements [Member] | Prepaid Expenses [Member]
Contingencies And Commitments [Line Items]
Upfront payment recorded as prepaid expense							2,100,000
Formal Settlement Payment to US Common Shareholders [Member]
Contingencies And Commitments [Line Items]
Aggregate settlement amount				$ 2,000,000
Formal Settlement Payment to US Common Shareholders [Member] | Maximum [Member]
Contingencies And Commitments [Line Items]
Aggregate settlement amount		$ 2,000,000
Letter of Credit [Member]
Contingencies And Commitments [Line Items]
Letters of credit secured by cash held in restricted depository account							$ 3,200,000	$ 3,200,000
Scenario Forecast [Member]
Contingencies And Commitments [Line Items]
Payment receivable under sublease agreement						$ 400,000
Scenario Forecast [Member] | Research Institutions [Member]
Contingencies And Commitments [Line Items]
Research and development expense					$ 100,000	500,000
Scenario Forecast [Member] | Research Agreements [Member]
Contingencies And Commitments [Line Items]
Research and development expense					2,800,000	4,700,000
Scenario Forecast [Member] | Intellectual Property Agreements [Member]
Contingencies And Commitments [Line Items]
Research and development expense					$ 100,000	$ 400,000
610 Main Street Sublease [Member]
Contingencies And Commitments [Line Items]
Lease expiration date			Dec. 31, 2026
Extended term of lease expiration			5 years
Operating Lease, Research Facility Space [Member]
Contingencies And Commitments [Line Items]
Lease expiration date							Feb. 28, 2022
[1]	Including the following amounts of research and development from a related party, see Note 15:

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Future Minimum Payments Required under Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	$ 6,275
2,020	6,866
2,021	7,072
2,022	5,874
2,023	5,855
Thereafter	18,639
Total minimum lease payments	$ 50,581

Significant Contracts - Additio

Significant Contracts - Additional Information (Detail) $ / shares in Units, € in Millions		Dec. 18, 2018USD ($)	Nov. 15, 2018USD ($)shares	Sep. 24, 2018USD ($)shares	Sep. 17, 2018USD ($)Installment	Feb. 12, 2016USD ($)	Jan. 29, 2016USD ($)$ / shares	Dec. 19, 2015USD ($)$ / shares	Oct. 26, 2015USD ($)Milestone	Dec. 18, 2018USD ($)	Oct. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015	Apr. 30, 2014USD ($)	Nov. 14, 2018USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)shares		Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)shares		Jan. 01, 2018USD ($)	Mar. 31, 2016	Nov. 30, 2014USD ($)	Nov. 30, 2014EUR (€)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Cost sharing expensed relating to patent maintenance, defense and prosecution, incurred																							$ 2,400,000		$ 1,200,000		$ 2,800,000
Cost sharing expensed relating to patent maintenance, defense and prosecution, accrued																							1,900,000		400,000
Research and development expense	[1]																						113,773,000		69,800,000		42,238,000
Collaboration revenue															$ 115,000	$ 563,000	$ 1,088,000	$ 1,358,000	$ 32,325,000	$ 2,387,000	$ 3,582,000	$ 2,703,000	3,124,000	[2]	40,997,000	[2]	5,164,000	[2]
Non-current deferred revenue															57,780,000				56,928,000				$ 57,780,000		56,928,000
Date of joint venture agreement																							Dec. 19, 2015
Cash contribution																											100,000
Gross proceeds from convertible debt																											35,010,000
Net proceeds from issuance of common shares											$ 35,000,000												$ 307,053,000		0		89,061,000
Other (expense) income																							(1,210,000)		(197,000)		78,512,000
Equity method investment																											36,500,000
Unrealized equity method losses																							(4,275,000)		(1,763,000)		(36,532,000)
Stock-based compensation expense																							39,260,000		20,636,000		10,844,000
Issuance of common shares, value																							307,053,000				88,664,000
Series B Redeemable Convertible Preferred Shares [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Debt instrument converted to Series B Preferred Shares, conversion price | $ / shares							$ 9.33
Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price allocation of arrangement consideration paid															91,200,000								91,200,000
Other (expense) income																											78,600,000
Remaining license fee																											15,000,000
ASU 2014-09 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-current deferred revenue																													$ 57,974,000
Standalone selling price allocation of arrangement consideration paid															106,300,000								106,300,000
Other (expense) income																											$ 79,100,000
ASU 2014-09 [Member] | Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue																							2,828,000
Non-current deferred revenue															57,030,000								57,030,000
Licensing Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price															71,400,000								71,400,000
Licensing Agreements [Member] | Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price															71,400,000								71,400,000
License and Patent Holder Consent [Member] | Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price allocation of arrangement consideration paid															63,600,000								63,600,000
License and Patent Holder Consent [Member] | ASU 2014-09 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price allocation of arrangement consideration paid															79,100,000								79,100,000
Future Research and Development Services [Member] | Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price allocation of arrangement consideration paid															600,000								$ 600,000
Common Stock [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Shares issued and sold | shares											2,500,000												9,960,526				7,100,000
Shares issued, price per share | $ / shares											$ 14
Issuance of common shares, value																							$ 311,000				$ 213,000
Bayer Convertible Loans [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Gross proceeds from convertible debt							$ 35,000,000	$ 35,000,000
Debt instrument converted to Series B Preferred Shares, conversion price | $ / shares								$ 13.43
Convertible Loan															35,000,000								35,000,000
Fair value of convertible loan															24,500,000								24,500,000
Loan agreement maturity date												Jan. 29, 2016
Bayer Convertible Loans [Member] | Series B Redeemable Convertible Preferred Shares [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Debt instrument converted to Series B Preferred Shares, conversion price | $ / shares							$ 13.43
Fair value of convertible loan							$ 24,500,000
Bayer Convertible Loans [Member] | Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Fair value of convertible loan															24,500,000								24,500,000
Standalone selling price allocation of arrangement consideration paid															27,000,000								27,000,000
Debt instrument discount															8,000,000								8,000,000
Debt instrument face amount															35,000,000								35,000,000
Bayer Convertible Loans [Member] | Adjusted Balance Under ASC 605 [Member] | Series B Redeemable Convertible Preferred Shares [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Loan agreement maturity date												Jan. 29, 2016
Bayer Convertible Loans [Member] | ASU 2014-09 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price allocation of arrangement consideration paid															27,200,000								27,200,000
Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense																							3,800,000		4,500,000		1,700,000
Collaboration revenue																							112,600,000
Reimbursements from research and license agreements																							900,000		4,400,000		0
Non-current deferred revenue															$ 0				100,000				$ 0		100,000
Date of formation of joint venture entity																							Feb. 12, 2016
Equity method investment, ownership percentage						50.00%									50.00%								50.00%							50.00%
Cash contribution						$ 100,000
Other payments due to company from joint venture entity						0
Cash contribution																							$ 100,000
Equity interest in the Joint Venture															$ 36,400,000								36,400,000
Convertible Loan															$ 35,000,000								35,000,000
Estimated revenue related to research and development services																							6,300,000
Stock-based compensation expense																							4,300,000		1,800,000		200,000
Unrecognized equity method losses in excess of Company's interest																							45,300,000		21,200,000
Operating expenses of joint venture																							53,400,000		36,300,000		80,800,000
Net loss of joint venture																							$ 52,500,000		36,200,000		80,800,000
Casebia Therapeutics LLP [Member] | Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Equity method investment, ownership percentage															50.00%								50.00%
Equity method investment															$ 0				0				$ 0		0
Casebia Therapeutics LLP [Member] | ASU 2014-09 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue																							112,600,000
Estimated revenue related to research and development services																							6,300,000
Research and Development Services [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price															6,300,000								6,300,000
Research and Development Services [Member] | Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Standalone selling price															6,300,000								6,300,000
Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense																							20,200,000		9,900,000		7,000,000
Nonrefundable upfront payment received									$ 75,000,000
Milestone payment receivable									420,000,000
Non-exclusive research revenue									19,300,000
Estimated standalone selling price for collaboration agreement									118,600,000
Revenue, Remaining Performance Obligation									82,000,000						57,900,000								57,900,000
Best estimate selling price for remaining research and development services									4,000,000
Best estimated selling price for collaboration agreement									158,600,000
Deferred revenue									80,000,000
Best estimate selling price for research and development services									4,000,000
Estimated selling price for collaboration agreement									40,000,000
Aggregate consideration receivable									131,000,000
Reimbursements from research and license agreements																							13,800,000
Non-current deferred revenue															$ 57,800,000				$ 57,900,000				57,800,000		57,900,000
Patent Assignment Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Clinical milestone payment payable																															$ 400,000	€ 0.3
Research and development expense																							0		0
Joint Development Agreement [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Nonrefundable upfront payment received									7,000,000
Up-front payment received																							$ 7,000,000
Agreement description																							In connection with entering into the JDA, the Company received a $7.0 million up-front payment from Vertex and is eligible for a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate. The net profits and net losses, as applicable, incurred under the JDA will be shared equally between the Company and Vertex.
Beta-Globin [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration									48,900,000
Best estimated selling price for single collaboration									48,900,000
Non-Exclusive Research License [Member] | Market-based Approach [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for collaboration agreement									1,000,000
Non-Exclusive Research License [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, Remaining Performance Obligation									500,000
Material Right to Discounts for Exclusive Licenses [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, Remaining Performance Obligation									57,700,000
Co-exclusive Development and Commercialization Licenses and Research License [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, Remaining Performance Obligation									23,800,000
Non-Exclusive Research License and Exclusive License to Develop [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate consideration receivable									98,200,000
Non-Exclusive Research License and Co-Exclusive License to Develop [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate consideration receivable									30,300,000
Non-Exclusive Research License and Co-Exclusive License to Develop [Member] | Vertex Pharmaceuticals Inc [Member] | Research and Development Services [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate consideration receivable									$ 2,500,000
Clinical Development And Regulatory Milestone [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of developmental milestone events | Milestone									9
Clinical Development Milestones [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable									$ 90,000,000
Regulatory Approval Milestone [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable									235,000,000
Commercial Milestones [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable									$ 75,000,000
Number of developmental milestone events | Milestone									2
Exercise Of Exclusive Option | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable									$ 10,000,000
Collaborative Arrangement Copromotion [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable									10,000,000
Commercial Milestone Event One [Member] | Vertex Pharmaceuticals Inc [Member] | Minimum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue									500,000,000
Commercial Milestone Event Two [Member] | Vertex Pharmaceuticals Inc [Member] | Minimum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue									1,000,000,000
Research Collaboration Agreement [Member] | ViaCyte [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense																							$ 15,000,000
Shares issued and sold | shares			214,512	165,636
Net proceeds from issuance of common shares										$ 7,500,000				$ 6,900,000
Other (expense) income																							$ (1,200,000)
Amount payable under collaboration agreement					$ 15,000,000
Number of installments for amount payable | Installment					2
Issuance of common shares, value			$ 8,100,000	$ 7,500,000
Key provisions of collaborative agreement description																							The agreement includes certain provisions such that in the event ViaCyte sold shares received from the Company for less than $15.0 million in combined net proceeds, the Company would owe ViaCyte the deficient amount. In the event ViaCyte sold shares received from the Company for greater than $15.0 million in combined net proceeds, ViaCyte would owe the Company the surplus amount.
Deficient amount payable														$ 600,000
Deficient amount paid in cash		$ 600,000
Total consideration paid																							$ 16,200,000
Collaboration agreement period					6 years
Research Collaboration Agreement [Member] | ViaCyte [Member] | Convertible Promissory Note [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Additional amount payable under certain circumstances					$ 10,000,000
Research and Development [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock-based compensation expense																							17,557,000		8,800,000		4,848,000
Research and Development [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Variable consideration received									19,300,000
Bayer Healthcare LLC [Member] | Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Equity method investment, ownership percentage																														50.00%
License [Member] | Bayer Healthcare LLC [Member] | Research and Development [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Fees paid																							0		0
Rights One [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration									45,600,000
Rights Two [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration									38,400,000
Rights Three [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration									17,300,000
Rights Four [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration									17,300,000
Unit One [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Best estimated selling price for single collaboration									55,600,000
Unit One [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, Remaining Performance Obligation									22,200,000
Unit One [Member] | Non-Exclusive Research License and Exclusive License to Develop [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate consideration receivable									34,400,000
Unit Two [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Best estimated selling price for single collaboration									48,400,000
Unit Two [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, Remaining Performance Obligation									18,700,000
Unit Two [Member] | Non-Exclusive Research License and Exclusive License to Develop [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate consideration receivable									30,000,000
Unit Three [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Best estimated selling price for single collaboration									27,300,000
Unit Three [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, Remaining Performance Obligation									8,400,000
Unit Three [Member] | Non-Exclusive Research License and Exclusive License to Develop [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate consideration receivable									16,900,000
Unit Four [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Best estimated selling price for single collaboration									27,300,000
Unit Four [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, Remaining Performance Obligation									8,400,000
Unit Four [Member] | Non-Exclusive Research License and Exclusive License to Develop [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate consideration receivable									$ 16,900,000
License and Service [Member] | Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue						35,000,000																	2,500,000		4,800,000		1,200,000
License and Service [Member] | Casebia Therapeutics LLP [Member] | Adjusted Balance Under ASC 605 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue																									4,800,000		1,200,000
License and Service [Member] | Casebia Therapeutics LLP [Member] | ASU 2014-09 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue																							2,500,000
License and Service [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue																							600,000		36,200,000		4,000,000
License and Service [Member] | Non-Exclusive Research License and Co-Exclusive License to Develop [Member] | Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate consideration receivable																									30,300,000
Royalty [Member] | Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue						$ 0
Technology Service [Member] | Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue																							34,900,000
CRISPR-Charpentier License Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Annual payments for consulting agreement																							$ 0		$ 0		$ 0
CRISPR-Charpentier License Agreement [Member] | License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Fees paid													$ 100,000
[1]	Including the following amounts of research and development from a related party, see Note 15:
[2]	Including the following amounts of revenue from a related party, see Note 15:

Share Capital - Additional Info

Share Capital - Additional Information (Detail)	1 Months Ended				12 Months Ended
	Sep. 30, 2018USD ($)$ / sharesshares	Aug. 31, 2018USD ($)	Jan. 31, 2018USD ($)$ / sharesshares	Oct. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018SFr / sharesshares	Dec. 31, 2017SFr / sharesshares	Dec. 31, 2016SFr / shares
Class of Stock [Line Items]
Common stock, shares authorized								52,183,139	41,092,969
Common shares, par value | SFr / shares								SFr 0.03	SFr 0.03	SFr 0.03
Unvested restricted stock award								327,342	366,401
Treasury stock, shares								307,936	444,873
Proceeds from issuance of common shares | $				$ 35,000,000	$ 307,053,000	$ 0	$ 89,061,000
Common shares reaquired				170,689
Common shares reaquired, value | $				$ 0
Common Stock, Voting Rights					one vote for each Common Share
Dividends declared and paid | $					$ 0
Sales Agreement With Jefferies LLC [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds | $		$ 125,000,000
IPO [Member]
Class of Stock [Line Items]
Issuance of common shares, net of issuance cost (in shares)				4,429,311
Common shares price per share | $ / shares				$ 14
Proceeds from issuance of common shares | $				$ 53,700,000
Overallotment Option [Member]
Class of Stock [Line Items]
Issuance of common shares, net of issuance cost (in shares)				429,311
Common shares price per share | $ / shares				$ 14
Equity Offering [Member]
Class of Stock [Line Items]
Issuance of common shares, net of issuance cost (in shares)	4,210,526		5,750,000
Common shares price per share | $ / shares	$ 47.50		$ 22.75
Proceeds from issuance of common shares | $	$ 187,600,000		$ 122,600,000
Stamp taxes on issuance proceeds | $					$ 3,100,000
Bayer Global Investments B.V [Member] | Private Placement [Member]
Class of Stock [Line Items]
Issuance of common shares, net of issuance cost (in shares)				2,500,000
Common shares price per share | $ / shares				$ 14
Proceeds from issuance of common shares | $				$ 35,000,000
Swiss Law [Member]
Class of Stock [Line Items]
Common stock, shares authorized								17,756,799	11,799,005
Debt Instruments [Member]
Class of Stock [Line Items]
Conditional capital reserved for future issuance								4,919,700	4,919,700
Unvested Restricted Share Award [Member]
Class of Stock [Line Items]
Unvested restricted stock award								22,341
Employee Benefit Plans [Member]
Class of Stock [Line Items]
Conditional capital reserved for future issuance								15,579,296	12,418,591

Equity-based Compensation - Opt

Equity-based Compensation - Option and Grant Plans - Additional Information (Detail) - Option and Grant Plans [Member] - shares	1 Months Ended		12 Months Ended
	May 31, 2018	May 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, options, vesting period			4 years
Share-based Compensation, options, contractual life			10 years
Number of options approved	4,000,000	2,012,684
Founder Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, requisite service period				4 years
IPO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award, number of shares granted			0

Equity-based Compensation - Sch

Equity-based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-Based compensation expense	$ 39,260	$ 20,636	$ 10,844
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-Based compensation expense	17,557	8,800	4,848
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-Based compensation expense	17,428	10,073	5,844
Loss from Equity Method Investment [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-Based compensation expense	$ 4,275	$ 1,763	$ 152

Equity-based Compensation - Fai

Equity-based Compensation - Fair Value of Employee and Non-employee Stock Option Award on the Grant Date Using the Black-Scholes Option-Pricing Model (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%
Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted	2,188,097	2,894,850	2,411,240
Weighted - average exercise price	$ 51.82	$ 16.92	$ 12.19
Weighted-average grant date fair value	$ 33.81	$ 10.86	$ 8.47
Weighted-average expected volatility	71.90%	72.10%	81.00%
Expected term (in years)	6 years	6 years	6 years
Weighted-average risk free interest rate	2.80%	2.00%	1.40%
Expected dividend yield	0.00%	0.00%	0.00%
Non Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted	21,500	104,997	215,710
Weighted - average exercise price	$ 42.75	$ 18.74	$ 19.54
Weighted-average grant date fair value	$ 34.74	$ 19.35	$ 17.38
Weighted-average expected volatility	77.90%	81.50%	88.20%
Expected term (in years)	10 years	9 years 4 months 24 days	10 years
Weighted-average risk free interest rate	3.00%	2.40%	2.40%
Expected dividend yield	0.00%	0.00%	0.00%

Equity-based Compensation - Sum

Equity-based Compensation - Summary of Stock Option Activity for Employees and Non-employees (Detail) - Employees and Non-employees [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options, Outstanding, Beginning Balance	6,262,339
Stock Options, Granted	2,209,597
Stock Options, Exercised	(946,131)
Stock Options, Cancelled or forfeited	(836,494)
Stock Options, Outstanding, Ending Balance	6,689,311	6,262,339
Stock Options, Exercisable	2,541,789
Stock Options, Vested or expected to vest	6,689,311
Weighted-Average Exercise Price, Outstanding, Beginning Balance	$ 13.24
Weighted-Average Exercise Price, Granted	51.73
Weighted-Average Exercise Price, Exercised	10.95
Weighted-Average Exercise Price, Cancelled or forfeited	20.11
Weighted-Average Exercise Price, Outstanding, Ending Balance	25.42	$ 13.24
Weighted-Average Exercise Price, Exercisable	15.74
Weighted-Average Exercise Price, Vested or expected to vest	$ 25.42
Weighted-Average Remaining Contractual Term	8 years 3 months 18 days	8 years 9 months 18 days
Weighted-Average Remaining Contractual Term, Exercisable	7 years 8 months 12 days
Weighted-Average Remaining Contractual Term, Vested or expected to vest	8 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding Balance	$ 68,572	$ 64,120
Aggregate Intrinsic Value, Exercisable	38,486
Aggregate Intrinsic Value, Vested or expected to vest	$ 68,572

Equity-based Compensation - Sha

Equity-based Compensation - Share Based Payment Activity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 83,300
Equity-based compensation expense not yet recognized, weighted-average service period for recognition	3 years
Stock-based compensation expense	$ 39,260	$ 20,636	$ 10,844
Founders' [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	300	800	$ 2,600
Weighted-Average Exercise Price, Vested or expected to vest			$ 12.65
Fay Corp Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation, number of shares issued			290,400
Fay Corp Awards [Member] | Founders' [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Transfer of vested shares			268,093
Departing Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 3,800	$ 2,200
Performance-Based [Member] | Vesting Percentage on First Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options, Granted	0	395,000
Share-based compensation, options, vested	790,598
Share-based compensation, options, outstanding	261,135
Market-Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options, Granted		150,000
Share-based compensation, options, vested	0
Share-based compensation, requisite service period	4 years
Share-based compensation, options, earned	150,000
Market-Based [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, eligible to receive		0
Market-Based [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, eligible to receive		150,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense not yet recognized, weighted-average service period for recognition	1 year 10 months 24 days
Total fair value of restricted stock vested	$ 11,300	$ 8,300
Total unrecognized compensation expenses	$ 10,200

Equity-based Compensation - S_2

Equity-based Compensation - Summary of the Company's Restricted Stock Activity (Detail)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common shares, Number of Shares, Beginning Balance	366,401
Unvested restricted common shares, Number of Shares, Granted	251,500
Unvested restricted common shares, Number of Shares, Vested	(246,286)
Unvested restricted common shares, Number of Shares, Cancelled or forfeited	(44,273)
Unvested restricted common shares, Number of Shares, Ending Balance	327,342
Restricted Stock Outstanding Upon Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common shares, Number of Shares, Beginning Balance	157,515
Unvested restricted common shares, Number of Shares, Granted	251,500
Unvested restricted common shares, Number of Shares, Vested	(77,673)
Unvested restricted common shares, Number of Shares, Cancelled or forfeited	(4,000)
Unvested restricted common shares, Number of Shares, Ending Balance	327,342
Restricted Stock Outstanding Upon Grant Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common shares, Number of Shares, Beginning Balance	208,886
Unvested restricted common shares, Number of Shares, Vested	(168,613)
Unvested restricted common shares, Number of Shares, Cancelled or forfeited	(40,273)
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 8.49
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Granted | $ / shares	44.51
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Vested | $ / shares	7.58
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Cancelled or forfeited | $ / shares	8.51
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Ending Balance | $ / shares	$ 36.72

401(k) Savings Plan - Additiona

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Company contributions toward the plan	$ 0.6	$ 0.5	$ 0.1

Income Taxes - Schedule of Loss

Income Taxes - Schedule of Loss Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Domestic	$ 5,966	$ 5,184	$ 3,322
Foreign	(170,394)	(71,792)	(26,040)
Total	$ (164,428)	$ (66,608)	$ (22,718)

Income Taxes - Schedule of (Pro

Income Taxes - Schedule of (Provision for) Benefit from Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income taxes:
Federal	$ (416)	$ (1,533)	$ (649)
State	(131)	(42)	11
Foreign		6	17
Total current income taxes	(547)	(1,569)	(621)
Deferred income taxes:
Federal	(6)	(477)	30
State		297	105
Foreign			2
Total deferred income taxes	(6)	(180)	137
Total income tax provision	$ (553)	$ (1,749)	$ (484)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Tax Expense Computed at Statutory Corporate Income Tax Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Effective Income Tax Rate
Income tax expense at statutory rate	9.30%	9.30%	10.30%
State income tax, net of federal benefit	0.70%	0.30%	1.30%
Nondeductible expenses	0.00%	0.00%	1.60%
Foreign rate differential	(0.40%)	(2.50%)	(3.30%)
Statutory to US GAAP permanent differences	1.00%	1.80%	6.60%
Stock-based compensation	1.40%	(2.90%)	(4.90%)
Research credits	1.80%	0.80%	3.10%
Change in valuation allowance	(14.10%)	(9.40%)	(16.80%)
Effective income tax rate	(0.30%)	(2.60%)	(2.10%)

Income Taxes - Schedule of Sign

Income Taxes - Schedule of Significant Components of Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 25,418	$ 9,987
Accruals and reserves	1,816	1,123
Deferred Rent	3,300	3,494
Other deferred tax assets	51	36
Stock based compensation	2,871
Deferred revenue	3,264	1,721
Research credit	3,322	543
Total deferred tax assets	40,042	16,904
Less valuation allowance	(36,208)	(13,041)
Net deferred tax assets	3,834	3,863
Deferred tax liabilities:
Depreciation	(3,785)	(3,791)
Intangible assets	(49)	(59)
Other deferred tax liabilities	(22)	(31)
Total deferred tax liabilities	(3,856)	(3,881)
Long term deferred taxes, liabilities	$ (22)	$ (18)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation Allowance [Line Items]
Corporate tax rate	9.30%	9.30%	10.30%
Non-US Net operating loss carryforwards	$ 541,100,000
Operating loss carryforwards expiration period	2,020
Domestic state research and development credit carryforwards	$ 1,800,000
Research and development credit carryforwards expiration period	2,033
Uncertain tax positions	$ 700,000
Unrecognized tax benefits, gross	1,595,000	$ 354,000	$ 163,000	$ 49,000
Unrecognized tax benefits would favorably impact the effective tax rate if recognized	1,500,000
Accrued interest or penalties related to uncertain tax positions	0	0	0
Uncertain tax positions recognized	0	$ 0	$ 0
U.S. Domestic Federal [Member] | Research and Development [Member]
Valuation Allowance [Line Items]
Uncertain tax positions	900,000
Tax credit carryforward amount	$ 1,900,000
Tax credit carryforward, expiration year	2,038
Maximum [Member]
Valuation Allowance [Line Items]
Corporate tax rate	21.00%	35.00%
Switzerland [Member]
Valuation Allowance [Line Items]
Increase in valuation allowance	$ 23,200,000

Income Taxes - Schedule of Aggr

Income Taxes - Schedule of Aggregate Changes in Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 354	$ 163	$ 49
Increases for tax positions taken during current period	1,212	178	134
Increases for tax positions taken in prior periods	29	13
Decreases for tax positions taken in prior periods			(20)
Balance at end of year	$ 1,595	$ 354	$ 163

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Collaboration revenue	$ 115	$ 563	$ 1,088	$ 1,358	$ 32,325	$ 2,387	$ 3,582	$ 2,703	$ 3,124	[1]	$ 40,997	[1]	$ 5,164	[1]
Total operating expenses	45,343	49,995	38,374	28,355	31,353	25,957	24,888	23,447	162,067		105,645		73,294
(Loss) income from operations	(45,228)	(49,432)	(37,286)	(26,997)	972	(23,570)	(21,306)	(20,744)	(158,943)		(64,648)		(68,130)
Net (loss) income	(47,590)	(50,711)	(38,380)	(28,300)	140	(24,707)	(22,315)	(21,475)	(164,981)		(68,357)		(23,202)
Net (loss) income attributable to common shareholders	$ (47,590)	$ (50,711)	$ (38,380)	$ (28,300)	$ 140	$ (24,707)	$ (22,315)	$ (21,475)	$ (164,981)		$ (68,357)		$ (23,177)
Net (loss) income per share attributable to common shareholders:
Basic	$ (0.92)	$ (1.07)	$ (0.82)	$ (0.62)	$ 0	$ (0.62)	$ (0.56)	$ (0.54)
Diluted	$ (0.92)	$ (1.07)	$ (0.82)	$ (0.62)	$ 0	$ (0.62)	$ (0.56)	$ (0.54)
Weighted-average common shares outstanding used in net (loss) income per share attributable to common shareholders:
Basic	51,688,383	47,391,988	46,842,316	45,877,428	40,509,897	40,088,718	39,895,938	39,725,947
Diluted	51,688,383	47,391,988	46,842,316	45,877,428	41,635,843	40,088,718	39,895,938	39,725,947
[1]	Including the following amounts of revenue from a related party, see Note 15:

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($)		Feb. 12, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Related Party Transaction [Line Items]
Collaboration revenue			$ 115,000	$ 563,000	$ 1,088,000	$ 1,358,000	$ 32,325,000	$ 2,387,000	$ 3,582,000	$ 2,703,000	$ 3,124,000	[1]	$ 40,997,000	[1]	$ 5,164,000	[1]
Research and development expense	[2]										113,773,000		69,800,000		42,238,000
Casebia Therapeutics LLP [Member]
Related Party Transaction [Line Items]
Collaboration revenue											112,600,000
Research and development expense											3,800,000		4,500,000		1,700,000
Reimbursements from research and license agreements											900,000		4,400,000		0
Casebia Therapeutics LLP [Member] | License and Service [Member]
Related Party Transaction [Line Items]
Collaboration revenue		$ 35,000,000									2,500,000		4,800,000		1,200,000
Research and Development Services [Member] | Casebia Therapeutics LLP [Member]
Related Party Transaction [Line Items]
Research and development expense											3,800,000		4,500,000		1,700,000
Reimbursements from research and license agreements											900,000		4,400,000		0
Research and Development Services [Member] | Casebia Therapeutics LLP [Member] | License and Service [Member]
Related Party Transaction [Line Items]
Collaboration revenue											2,500,000		$ 4,800,000		$ 1,200,000
Collaboration Agreement [Member] | Vertex Pharmaceuticals Inc [Member]
Related Party Transaction [Line Items]
Research and development expense											20,200,000
Reimbursements from research and license agreements											$ 13,800,000
Collaboration Agreement [Member] | Vertex Pharmaceuticals Inc [Member] | Minimum [Member]
Related Party Transaction [Line Items]
Voting interest Percentage											10.00%
Collaboration Agreement [Member] | License and Service [Member] | Vertex Pharmaceuticals Inc [Member]
Related Party Transaction [Line Items]
Collaboration revenue											$ 600,000
[1]	Including the following amounts of revenue from a related party, see Note 15:
[2]	Including the following amounts of research and development from a related party, see Note 15: