CRISPR Therapeutics (CRSP) 10-Q 29 Apr 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 25, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	CRSP
Entity Registrant Name	CRISPR THERAPEUTICS AG
Entity Central Index Key	0001674416
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		52,909,973

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 437,549	$ 456,649
Accounts receivable, including related party amounts of $331 and $88 as of March 31, 2019 and December 31, 2018, respectively	331	88
Prepaid expenses and other current assets, including related party amounts of $4,775 and $3,417 as of March 31, 2019 and December 31, 2018, respectively	11,916	9,658
Total current assets	449,796	466,395
Property and equipment, net	18,871	18,500
Intangible assets, net	276	289
Restricted cash	3,163	3,163
Operating lease assets	25,098
Other non-current assets	669	669
Total assets	497,873	489,016
Current liabilities:
Accounts payable	7,131	5,069
Accrued expenses, including related party amounts of $2,483 and $1,700 as of March 31, 2019 and December 31, 2018, respectively	15,680	20,852
Accrued tax liabilities	615	402
Deferred rent		1,202
Operating lease liabilities	4,899
Other current liabilities	73	221
Total current liabilities	28,398	27,746
Deferred revenue non-current, including related party amounts of $57,755 and $57,780 as of March 31, 2019 and December 31, 2018, respectively	57,755	57,780
Deferred rent non-current		11,052
Operating lease liabilities, net of current portion	31,728
Other non-current liabilities	182	243
Total liabilities	118,063	96,821
Commitments and contingencies, see Note 5
Shareholders’ equity:
Common shares, CHF 0.03 par value, 53,325,963 and 52,183,139 shares authorized at March 31, 2019 and December 31, 2018, respectively, 52,943,581 and 52,160,798 shares issued at March 31, 2019 and December 31, 2018, respectively, 52,635,645 and 51,852,862 shares outstanding at March 31, 2019 and December 31, 2018, respectively, 20,498,996 shares in conditional capital at March 31, 2019 and December 31, 2018.	1,589	1,584
Treasury shares, at cost, 307,936 shares at March 31, 2019 and December 31, 2018	(57)	(57)
Additional paid-in capital	718,255	682,245
Accumulated deficit	(339,977)	(291,569)
Accumulated other comprehensive loss		(8)
Total shareholders' equity	379,810	392,195
Total liabilities and shareholders’ equity	$ 497,873	$ 489,016

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) $ in Thousands	Mar. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares
Statement Of Financial Position [Abstract]
Accounts receivable, related party amount, current | $	$ 331	$ 88
Prepaid expenses and other current assets, related party amount | $	4,775	3,417
Accrued expenses related party amount, current | $	2,483	1,700
Deferred revenue non-current related party amount | $	$ 57,755	$ 57,780
Common stock, shares authorized	53,325,963	52,183,139
Common stock, shares issued	52,943,581	52,160,798
Common stock, shares outstanding	52,635,645	51,852,862
Common stock, conditional capital	20,498,996	20,498,996
Treasury stock, shares	307,936	307,936

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Collaboration revenue	[1]	$ 328	$ 1,358
Operating expenses:
Research and development	[2]	33,822	19,519
General and administrative		14,929	8,836
Total operating expenses		48,751	28,355
Loss from operations		(48,423)	(26,997)
Other income (expense):
Loss from equity method investment		(1,025)	(1,091)
Other income (expense), net		1,125	(126)
Total other income (expense), net		100	(1,217)
Net loss before income taxes		(48,323)	(28,214)
Provision for income taxes		(85)	(86)
Net loss		(48,408)	(28,300)
Foreign currency translation adjustment		8	12
Comprehensive loss		(48,400)	(28,288)
Reconciliation of net loss to net loss attributable to common shareholders:
Net loss		$ (48,408)	$ (28,300)
Net loss per share attributable to common shareholders—basic and diluted		$ (0.93)	$ (0.62)
Weighted-average common shares outstanding used in net loss per share attributable to common shareholders—basic and diluted		52,093,208	45,877,428
[1]	Including the following revenue from a related party, see Notes 6 & 11:
[2]	Including the following research and development expense with a related party, see Notes 6 & 11:

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue from related party	$ 328	$ 1,082
Research and development expense with a related party	$ 7,587	$ 1,106

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Shares [Member]	Treasury Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2017	$ 187,832	$ 1,240		$ 312,018	$ (125,440)	$ 14
Beginning 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)
Issuance of common stock, net of issuance costs	122,597	$ 174		122,423
Issuance of common stock, net of issuance costs (in shares)		5,750,000
Vesting of restricted shares, value	13			13
Vesting of restricted shares (in shares)		10,042
Exercise of vested options, value	2,656	$ 9		2,647
Exercise of vested options (in shares)		328,525	(6,253)
Stock-based compensation expense	6,673			6,673
Other comprehensive loss	12					12
Net loss	(28,300)				(28,300)
Ending balance at Mar. 31, 2018	290,335	$ 1,423		443,774	(154,888)	26
Ending balance (in shares) at Mar. 31, 2018		46,680,815	438,620
Beginning balance at Dec. 31, 2018	392,195	$ 1,584	$ (57)	682,245	(291,569)	(8)
Beginning balance (in shares) at Dec. 31, 2018		51,852,862	307,936
Issuance of common stock, net of issuance costs	23,472			23,472
Issuance of common stock, net of issuance costs (in shares)		631,580
Vesting of restricted shares, value	15			15
Vesting of restricted shares (in shares)		9,288
Exercise of vested options, value	$ 1,832	$ 5		1,827
Exercise of vested options (in shares)	148,743	141,915
Stock-based compensation expense	$ 10,696			10,696
Other comprehensive loss	8					$ 8
Net loss	(48,408)				(48,408)
Ending balance at Mar. 31, 2019	$ 379,810	$ 1,589	$ (57)	$ 718,255	$ (339,977)
Ending balance (in shares) at Mar. 31, 2019		52,635,645	307,936

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2019SFr / shares	Mar. 31, 2018SFr / shares
Common shares, par value			SFr 0.03
Common Shares [Member]
Issuance costs | $	$ 1.2	$ 8.2
Common shares, par value			SFr 0.03	SFr 0.03

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net loss	$ (48,408)	$ (28,300)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	812	826
Equity-based compensation	9,671	5,582
Loss from equity method investment	1,025	1,091
Changes in:
Accounts receivable	(243)	1,366
Prepaid expenses and other assets	(3,051)	(2,426)
Accounts payable and accrued expenses	(3,324)	(439)
Deferred revenue	(25)	(218)
Deferred rent		(195)
Other liabilities, net	(194)	25
Net cash used in operating activities	(43,737)	(22,688)
Investing activities:
Purchase of property and equipment	(1,097)	(555)
Net cash used in investing activities	(1,097)	(555)
Financing activities:
Proceeds from issuance of common shares, net of issuance costs	23,894	122,597
Proceeds from exercise of options	1,832	2,654
Net cash provided by financing activities	25,726	125,251
Effect of exchange rate changes on cash	8	12
(Decrease) increase in cash	(19,100)	102,020
Cash, cash equivalents and restricted cash, beginning of period	459,812	242,912
Cash, cash equivalents and restricted cash, end of period	440,712	344,932
Supplemental disclosure of non-cash investing and financing activities
Property and equipment purchases in accounts payable and accrued expenses	579	$ 307
Equity issuance costs in accounts payable and accrued expenses	$ 181

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Reconciliation to amounts within the condensed consolidated balance sheets
Cash and cash equivalents	$ 437,549	$ 456,649	$ 341,767
Restricted cash	3,163	3,163	3,165
Cash, cash equivalents and restricted cash at end of period	$ 440,712	$ 459,812	$ 344,932	$ 242,912

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	1. Basis of Presentation and Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the financial position and results of operations for the interim periods ended March 31, 2019 and 2018. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements for the year ended December 31, 2018, which are contained in the 2018 Annual Report on Form 10-K. Use of Estimates 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. Significant estimates in these consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses and equity-based compensation expense. The Company bases its estimates on historical experience and various other assumptions, including in certain circumstances future projections that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Changes in estimates are reflected in reported results in the period in which they become known. Significant Accounting Policies The significant accounting policies used in preparation of these condensed consolidated financial statements for the three months ended March 31, 2019 are consistent with those discussed in Note 2 to the consolidated financial statements in the Company’s 2018 Annual Report on Form 10-K, except with respect to the Company’s lease accounting policy noted within the “Recently adopted accounting standards” section below. Recently Adopted Accounting Standards The Company adopted ASC 842, Leases Impact of Adopting ASC 842 on the Financial Statements January 1, 2019 Prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 As Adjusted Consolidated Balance Sheet Data (in thousands): Prepaid expenses and other current assets (1) $ 9,658 $ (553 ) $ 9,105 Operating lease assets (2) $ — $ 26,087 $ 26,087 Deferred rent (3)(4) $ 1,026 $ (1,026 ) $ — Deferred rent non-current (3) $ 11,052 $ (11,052 ) $ — Operating lease liabilities (5) $ — $ 4,930 $ 4,930 Non-current operating lease liabilities (5) $ — $ 32,682 $ 32,682 (1) Represents reclassification of prepaid rent to operating lease assets. (2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets. (3) Represents reclassification of deferred rent and tenant incentives to operating lease assets. (4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019. (5) Represents recognition of operating lease liabilities.

Property and Equipment, net

Property and Equipment, net	3 Months Ended
	Mar. 31, 2019
Property Plant And Equipment [Abstract]
Property and Equipment, net	2. Property and Equipment, net Property and equipment, net, consists of the following (in thousands): As of March 31, December 31, 2019 2018 Computer equipment $ 592 $ 443 Furniture, fixtures and other 2,453 2,453 Laboratory equipment 9,571 8,964 Leasehold improvements 13,776 13,776 Construction work in process 825 239 Total property and equipment, gross 27,217 25,875 Accumulated depreciation (8,346 ) (7,375 ) Total property and equipment, net $ 18,871 $ 18,500 Depreciation expense for the three months ended March 31, 2019 and 2018 was $1.0 million and $0.8 million, respectively.

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Accrued Expenses	3. Accrued Expenses Accrued expenses consist of the following (in thousands): As of March 31, December 31, 2019 2018 Payroll and employee-related costs $ 3,834 $ 7,321 Research costs 8,023 7,973 Licensing fees 105 625 Professional fees 2,446 1,848 Intellectual property costs 1,101 2,193 Accrued property and equipment 103 294 Other 68 598 Total $ 15,680 $ 20,852

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	4. Commitments and Contingencies Litigation In the ordinary course of business, we are from time to time involved in lawsuits, claims, investigations, proceedings, and threats of litigation relating to intellectual property, commercial arrangements, employment and other matters. While the outcome of these proceedings and claims cannot be predicted with certainty, we are not party to any legal or arbitration proceedings that may have significant effects on our financial position. We are not a party to any material proceedings in which any director, member of executive management or affiliate of ours is either a party adverse to us or our subsidiaries or has a material interest adverse to us or our subsidiaries. Letters of Credit As of March 31, 2019, the Company had restricted cash of $3.2 million representing letters of credit securing the Company’s obligations under certain leased facilities in Cambridge, Massachusetts, 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 March 31, 2019. Research Agreements The Company has engaged several research institutions and companies to identify new delivery strategies and applications of the gene-editing technology. 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, as well as 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 of $2.1 million and $1.9 million in 2019 and 2020, respectively. For the three months ended March 31, 2019, the Company paid $1.7 million related to these research agreements. The Company is also 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 paid $4.0 million in upfront payments, which were recorded as prepaid expenses as of March 31, 2019. The Company will amortize the prepaid balance as services are performed.

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	5. Leases In June 2015, the Company entered into a lease agreement for the lease of approximately 19,817 square feet of research facility space with a commencement date of November 15, 2015 (the “2015 Lease”). The lease expires in February 2022. The 2015 Lease contains escalating rent clauses which require higher rent payments in future years. With the adoption of ASC 842, the Company has recorded a right-of-use asset and corresponding lease liability. In May 2016, the Company entered into a sublease agreement for its primary office and research facility in Cambridge, Massachusetts, with a commencement date of December 23, 2016 (the “2016 Sublease”). The sublease expires in December 2026 with an option to extend the term of sublease for an additional five-year period if, at the time of expiration of the initial term, the sublessor does not intend to utilize the space for itself or its affiliates. The 2016 Sublease contains escalating rent clauses which require higher rent payments in future years. With the adoption of ASC 842, the Company has recorded a right-of-use asset and corresponding lease liability. The right-of-use asset and corresponding lease liability does not include the additional five-year period under the option. In addition, the Company rents certain offices space in Zug, Switzerland, on a short-term basis for which a right-of-use asset and liability are not recorded, in accordance with the practical expedient elected. The Company has embedded leases in certain research and license agreements for which the Company has recorded a right of use asset and liability. These arrangements are not significant in comparison to the Company’s total operating lease assets and liabilities. In addition, the Company has identified certain short-term leases embedded within its manufacturing contracts which are not recorded on the Company’s balance sheet in accordance with the practical expedient elected. The Company identified and assessed the following estimates in recognizing the right-of-use asset and corresponding liability: • Expected lease term : The expected lease term for those leases commencing prior to January 1, 2019 did not change with the adoption of ASC 842. The expected lease term for leases commencing after the adoption of ASC 842 includes noncancelable lease periods and, when applicable, periods covered by an option to extend the lease if the Company is reasonably certain to exercise that option, as well as periods covered by an option to terminate the lease if the Company is reasonably certain not to exercise that option. • Incremental borrowing rate : As the discount rates in the Company’s lease are not implicit, the Company estimated the incremental borrowing rate based on the rate of interest the Company would have to pay to borrow a similar amount on a collateralized basis over a similar term. The following table summarizes the lease assets and liabilities as of March 31, 2019 (in thousands): As of March 31, 2019 Assets Operating lease assets $ 25,098 Total lease assets 25,098 Liabilities Current Operating lease liabilities 4,899 Non-current Operating lease liabilities, net of current portion 31,728 Total lease liabilities $ 36,627 The following table summarizes operating lease costs included in research and development and general and administrative expense, as well as sublease income for the three months ended March 31, 2019 (in thousands): Three months ended March 31, 2019 Operating lease costs $ 1,822 Short-term lease costs 1,138 Variable lease costs 730 Sublease income (525 ) Net lease cost $ 3,165 The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of March 31, 2019 (in thousands): Total 2019 $ 6,367 2020 6,866 2021 7,072 2022 5,874 2023 5,855 Thereafter 18,639 Total $ 50,673 Present value adjustment (14,046 ) Present value of lease liabilities $ 36,627 The following table summarizes the lease term and discount rate as of March 31, 2019: As of March 31, 2019 Weighted-average remaining lease term (years) Operating leases 7.2 Weighted-average discount rate Operating leases 9.7 % The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the three months ended March 31, 2019 (in thousands): Three months ended March 31 2019 Cash paid for amounts included in the measurement of lease liabilities $ 1,818 Operating cash flows from operating leases $ 1,818

Significant Contracts

Significant Contracts	3 Months Ended
	Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Significant Contracts	6. Significant Contracts Collaboration Agreement with and Joint Development Agreement with Vertex Pharmaceuticals, Inc. Summary of Agreement On October 26, 2015, the Company entered into a strategic collaboration, option and license agreement (“Collaboration Agreement”) with Vertex Pharmaceuticals, Inc. (“Vertex”). The Collaboration Agreement is focused on the use of the Company’s CRISPR/Cas9 gene editing technology 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. In connection with the Collaboration Agreement, Vertex made a nonrefundable upfront payment of $75.0 million. Under the Collaboration Agreement, Vertex will fund 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 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 sales. In connection with 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 The arrangements include components of a customer-vendor relationship and collaborative arrangements as defined under ASC 808, Collaborative Arrangements Revenue from Contracts with Customers Accounting Analysis Under ASC 606 As the overall arrangement was modified in December 2017, the Company elected a practical expedient within ASC 606 that allowed entities to reflect the aggregate effect of all contract modifications when identifying the satisfied and unsatisfied performance obligations for contracts that were modified prior to the adoption of ASC 606. As of the December 2017 contract modification date, the Company concluded the arrangement contained 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 research and development (“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. 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, the Company recognizes revenue related to the R&D Services as invoiced, in line with the practical expedient in ASC 606-10-55-18. The transaction price was 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 is 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 recognized $0.1 million and $0.2 million of revenue related to the collaboration with Vertex for the three months ended March 31, 2019 and 2018, respectively. As of March 31, 2019, there was $57.8 million of non-current deferred revenue related to the collaboration with Vertex, which is unchanged from December 31, 2018. The transaction price allocated to the remaining performance obligations is $57.9 million. The remaining performance obligations will be recognized as follows: four material rights to obtain an exclusive commercialization and development license at a point in time, upon exercise; and the non-exclusive research license ratably over/within the remaining two-and-a-half-year research term. As of March 31, 2019, the remaining amount to be recognized for the non-exclusive research license is not significant. R&D Services are recognized as invoiced under the practical expedient and, as such, are not disclosed within the remaining performance obligation balance. Milestones under the Collaboration Agreement The Company evaluated 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 Milestone Events 1. Initiation of the first Clinical Trial of a Product 2. Establishment of Proof of Concept for a Product 3. Initiation of the first Phase 3 Clinical Trial of a Product 4. Acceptance of Approval Application by the U.S. Food and Drug Administration for a Product 5. Acceptance of Approval Application by the European Medicines Agency for a Product 6. Acceptance of Approval Application by a Regulatory Authority in Japan for a Product 7. Marketing Approval in the U.S. 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; and 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 CRISPR/Cas9 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 are accounted for under the royalty recognition constraint and will be accounted for as constrained variable consideration. The Company applies 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. Accounting Analysis under ASC 808 The Company identified the following collaborative elements which are accounted for under ASC 808: (i) development and commercialization services for shared products; (ii) R&D Services for follow-on products; and (iii) committee participation. The related impact of the cost sharing associated with research and development is included in research and development expense. Expenses related to services performed by the Company are classified as research and development expense. Payments received from Vertex for partial reimbursement of expenses are recorded as a reduction of research and development expense. The Company recognized $7.1 million and $4.4 million of research and development expense related to the collaboration with Vertex for the three months ended March 31, 2019 and 2018, respectively. Research and development expense for the three months ended March 31, 2019 and 2018 was net of $4.5 million and $3.1 million of reimbursements from Vertex, respectively. Joint Venture with Bayer Healthcare LLC On December 19, 2015, the Company entered into an agreement with Bayer Healthcare LLC (“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 Therapeutics LLP (“Casebia”). 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 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 also entered into a separate services agreement with Casebia, under which the Company agreed to provide compensated research and development services. During 2016, the Company recorded an equity method investment of $36.5 million equal to the fair value of the Company’s interest in Casebia and subsequently recorded unrealized equity method losses for the same amount. The Company has no further contractual obligations to provide cash financing to Casebia and accordingly, no additional losses have been recorded beyond the initial equity amount. Casebia’s net losses were $14.2 million and $12.5 million for the three months ended March 31, 2019 and 2018, respectively. Unrecognized equity method losses in excess of the Company’s equity investment in Casebia were $51.9 million and $45.3 million as of March 31, 2019 and December 31, 2018, respectively. The remaining performance obligations include research and development services, which are recorded as revenue under ASC 606 and cost sharing activities with Casebia related to shared research and technology licenses are accounted for as a cost/profit sharing arrangement under ASC 808, with the related impact of the cost sharing included as research and development expense. During the three months ended March 31, 2019 and 2018, the Company recognized $0.2 million and $1.1 million of revenue, respectively, related to the collaboration with Casebia. During the three months ended March 31, 2019 and 2018, the Company recognized $0.5 million and $1.1 million, respectively, of research and development expense, related to the collaboration with Casebia. During the three months ended March 31, 2019 and 2018, the Company recognized a loss from equity method investment of $1.0 million and $1.1 million, respectively, related to stock-based compensation expense for Casebia employees.

Share Capital

Share Capital	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Share Capital	7. Share Capital The Company had 53,325,963 authorized common shares as of March 31, 2019, with a par value of CHF 0.03 per share. Included in the authorized common shares as of March 31, 2019 are 13,962 shares of unvested restricted stock awards, 307,936 treasury shares which are legally outstanding but not considered outstanding for accounting purposes and 368,420 shares registered and reserved for future issuance. The Company had conditional capital reserved for future issuance of 15,579,296 common shares for employee benefit plans and 4,919,700 common shares for debt instruments as of March 31, 2019. Under Swiss law, authorized share capital consisted of 17,756,799 common shares as of March 31, 2019. At-the-Market Offering In August 2018, the Company entered into an At-The-Market (“ATM”) sales agreement with Jefferies LLC (“Jefferies”), under which Jefferies may offer and sell, from time to time, common shares having aggregate gross proceeds of up to $125.0 million. In the first quarter of 2019, we began to issue and sell securities under this sales agreement. During the three months ended March 31, 2019, the Company sold 631,580 shares of common stock for net cash proceeds of $23.9 million, after deducting commission fees of $0.7 million. The Company sold an additional 493,017 shares of common stock under this agreement subsequent to March 31, 2019 through April 29, 2019, resulting in net cash proceeds of approximately $18.7 million.

Stock-based Compensation

Stock-based Compensation	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	8. Stock-based Compensation During the three months ended March 31, 2019 and 2018, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 4,962 $ 2,916 General and administrative 4,709 2,666 Loss from equity method investment 1,025 1,091 Total $ 10,696 $ 6,673 Stock option activity The following table summarizes stock option activity for the three months ended March 31, 2019 (intrinsic value in thousands): Stock Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2018 6,689,311 $ 25.42 8.3 $ 68,572 Granted 1,545,573 $ 35.25 Exercised (148,743 ) $ 13.35 Cancelled or forfeited (53,559 ) $ 39.57 Outstanding at March 31, 2019 8,032,582 $ 27.44 8.5 $ 102,371 Exercisable at March 31, 2019 2,798,109 $ 17.17 7.7 $ 58,010 Vested and expected to vest at March 31, 2019 8,032,582 $ 27.44 8.5 $ 102,371 The Company estimated the fair value of each stock option award using the Black-Scholes option-pricing model based on the following assumptions: Three Months Ended March 31, 2019 2018 Assumptions Weighted-average expected volatility 69.3 % 70.5 % Expected term (in years) 6.0 6.0 Risk-free interest rate 2.5 % 2.7 % Expected dividend yield 0.0 % 0.0 % As of March 31, 2019, total unrecognized compensation expense related to stock options was $107.6 million which the Company expects to recognize over a remaining weighted-average period of 3.1 years. Restricted stock activity The following table summarizes restricted stock activity for the three months ended March 31, 2019: Restricted Stock Weighted- Average Grant Date Fair Value Unvested balance as of December 31, 2018 327,342 $ 36.72 Granted 40,000 32.06 Vested (10,046 ) 4.88 Cancelled or forfeited (12,000 ) 38.33 Unvested balance as of March 31, 2019 345,296 $ 37.05 As of March 31, 2019, total unrecognized compensation expense related to unvested restricted common shares was $9.4

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Shareholders	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Shareholders	9. Basic net loss per share is calculated by dividing net 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 common share equivalents, presented on an as-converted basis, were excluded from the calculation of net loss per share for the periods presented due to their anti-dilutive effect (in common stock equivalent shares): As of March 31, 2019 March 31, 2018 Outstanding options 8,032,582 6,638,120 Unvested restricted common shares 345,296 147,472 Total 8,377,878 6,785,592

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes During the three months ended March 31, 2019 and 2018, the Company recorded an income tax provision of $0.1 million and $0.1 million, respectively, representing an effective tax rate of -0.2% and -0.3%, respectively. The income tax provision is primarily attributable to the year-to-date pre-tax income earned by the Company’s U.S. subsidiary. The difference in the statutory tax rate and effective tax rate is primarily a result of the jurisdictional mix of earnings and losses that are not benefited. The Company maintains a valuation allowance against certain deferred tax assets that are not more-likely-than-not realizable. As a result, the Company has not recognized a tax benefit related to losses generated in Switzerland in the current periods.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	11. Related Party Transactions In the fourth quarter of 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 “Collaboration Agreement with and Joint Development Agreement with Vertex Pharmaceuticals, Inc. Joint Venture with Bayer Healthcare LLC

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the financial position and results of operations for the interim periods ended March 31, 2019 and 2018. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements for the year ended December 31, 2018, which are contained in the 2018 Annual Report on Form 10-K.
Use of Estimates	Use of Estimates 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. Significant estimates in these consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses and equity-based compensation expense. The Company bases its estimates on historical experience and various other assumptions, including in certain circumstances future projections that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Changes in estimates are reflected in reported results in the period in which they become known.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards The Company adopted ASC 842, Leases Impact of Adopting ASC 842 on the Financial Statements January 1, 2019 Prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 As Adjusted Consolidated Balance Sheet Data (in thousands): Prepaid expenses and other current assets (1) $ 9,658 $ (553 ) $ 9,105 Operating lease assets (2) $ — $ 26,087 $ 26,087 Deferred rent (3)(4) $ 1,026 $ (1,026 ) $ — Deferred rent non-current (3) $ 11,052 $ (11,052 ) $ — Operating lease liabilities (5) $ — $ 4,930 $ 4,930 Non-current operating lease liabilities (5) $ — $ 32,682 $ 32,682 (1) Represents reclassification of prepaid rent to operating lease assets. (2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets. (3) Represents reclassification of deferred rent and tenant incentives to operating lease assets. (4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019. (5) Represents recognition of operating lease liabilities.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2019
ASC 842 [Member]
Impact of Adoption ASC 842 on the Financial Statements	Impact of Adopting ASC 842 on the Financial Statements January 1, 2019 Prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 As Adjusted Consolidated Balance Sheet Data (in thousands): Prepaid expenses and other current assets (1) $ 9,658 $ (553 ) $ 9,105 Operating lease assets (2) $ — $ 26,087 $ 26,087 Deferred rent (3)(4) $ 1,026 $ (1,026 ) $ — Deferred rent non-current (3) $ 11,052 $ (11,052 ) $ — Operating lease liabilities (5) $ — $ 4,930 $ 4,930 Non-current operating lease liabilities (5) $ — $ 32,682 $ 32,682 (1) Represents reclassification of prepaid rent to operating lease assets. (2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets. (3) Represents reclassification of deferred rent and tenant incentives to operating lease assets. (4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019. (5) Represents recognition of operating lease liabilities.

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	3 Months Ended
	Mar. 31, 2019
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net, consists of the following (in thousands): As of March 31, December 31, 2019 2018 Computer equipment $ 592 $ 443 Furniture, fixtures and other 2,453 2,453 Laboratory equipment 9,571 8,964 Leasehold improvements 13,776 13,776 Construction work in process 825 239 Total property and equipment, gross 27,217 25,875 Accumulated depreciation (8,346 ) (7,375 ) Total property and equipment, net $ 18,871 $ 18,500

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): As of March 31, December 31, 2019 2018 Payroll and employee-related costs $ 3,834 $ 7,321 Research costs 8,023 7,973 Licensing fees 105 625 Professional fees 2,446 1,848 Intellectual property costs 1,101 2,193 Accrued property and equipment 103 294 Other 68 598 Total $ 15,680 $ 20,852

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Summary of Lease Assets and Liabilities	The following table summarizes the lease assets and liabilities as of March 31, 2019 (in thousands): As of March 31, 2019 Assets Operating lease assets $ 25,098 Total lease assets 25,098 Liabilities Current Operating lease liabilities 4,899 Non-current Operating lease liabilities, net of current portion 31,728 Total lease liabilities $ 36,627
Summary of Operating Lease Costs Included in Research and Development and General and Administrative Expense, as well as Sublease Income	The following table summarizes operating lease costs included in research and development and general and administrative expense, as well as sublease income for the three months ended March 31, 2019 (in thousands): Three months ended March 31, 2019 Operating lease costs $ 1,822 Short-term lease costs 1,138 Variable lease costs 730 Sublease income (525 ) Net lease cost $ 3,165
Summary of Maturity of Undiscounted Payments Due under Lease Liabilities and Present Value of Those Liabilities	The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of March 31, 2019 (in thousands): Total 2019 $ 6,367 2020 6,866 2021 7,072 2022 5,874 2023 5,855 Thereafter 18,639 Total $ 50,673 Present value adjustment (14,046 ) Present value of lease liabilities $ 36,627
Summary of Lease Term and Discount Rate	The following table summarizes the lease term and discount rate as of March 31, 2019: As of March 31, 2019 Weighted-average remaining lease term (years) Operating leases 7.2 Weighted-average discount rate Operating leases 9.7 %
Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities	The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the three months ended March 31, 2019 (in thousands): Three months ended March 31 2019 Cash paid for amounts included in the measurement of lease liabilities $ 1,818 Operating cash flows from operating leases $ 1,818

Stock-based Compensation (Table

Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock-Based Compensation Expense	During the three months ended March 31, 2019 and 2018, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 4,962 $ 2,916 General and administrative 4,709 2,666 Loss from equity method investment 1,025 1,091 Total $ 10,696 $ 6,673
Summary of Stock Option Activity	The following table summarizes stock option activity for the three months ended March 31, 2019 (intrinsic value in thousands): Stock Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2018 6,689,311 $ 25.42 8.3 $ 68,572 Granted 1,545,573 $ 35.25 Exercised (148,743 ) $ 13.35 Cancelled or forfeited (53,559 ) $ 39.57 Outstanding at March 31, 2019 8,032,582 $ 27.44 8.5 $ 102,371 Exercisable at March 31, 2019 2,798,109 $ 17.17 7.7 $ 58,010 Vested and expected to vest at March 31, 2019 8,032,582 $ 27.44 8.5 $ 102,371
Assumptions to Estimate Fair Value of Stock Option Award Using the Black-Scholes Option-Pricing Model	The Company estimated the fair value of each stock option award using the Black-Scholes option-pricing model based on the following assumptions: Three Months Ended March 31, 2019 2018 Assumptions Weighted-average expected volatility 69.3 % 70.5 % Expected term (in years) 6.0 6.0 Risk-free interest rate 2.5 % 2.7 % Expected dividend yield 0.0 % 0.0 %
Summary of Restricted Stock Activity	The following table summarizes restricted stock activity for the three months ended March 31, 2019: Restricted Stock Weighted- Average Grant Date Fair Value Unvested balance as of December 31, 2018 327,342 $ 36.72 Granted 40,000 32.06 Vested (10,046 ) 4.88 Cancelled or forfeited (12,000 ) 38.33 Unvested balance as of March 31, 2019 345,296 $ 37.05

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Shareholders (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Calculation of Net Loss per Share	The following common share equivalents, presented on an as-converted basis, were excluded from the calculation of net loss per share for the periods presented due to their anti-dilutive effect (in common stock equivalent shares): As of March 31, 2019 March 31, 2018 Outstanding options 8,032,582 6,638,120 Unvested restricted common shares 345,296 147,472 Total 8,377,878 6,785,592

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Net lease assets	$ 25,098
Net lease liabilities	$ 36,627
ASC 842 [Member]
Summary Of Significant Accounting Policies [Line Items]
Net lease assets		$ 26,087
Net lease liabilities		$ 37,600

Basis of Presentation and Sig_5

Basis of Presentation and Significant Accounting Policies - Impact of Adopting ASC 842 on Financial Statements (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets	$ 11,916		$ 9,658
Operating lease assets	25,098
Deferred rent			1,202
Deferred rent non-current			$ 11,052
Operating lease liabilities	4,899
Non-current operating lease liabilities	$ 31,728
ASC 842 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets		$ 9,105
Operating lease assets		26,087
Operating lease liabilities		4,930
Non-current operating lease liabilities		32,682
Prior [Member] | ASC 842 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets		9,658
Deferred rent		1,026
Deferred rent non-current		11,052
Adjustment [Member] | ASC 842 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets		(553)
Operating lease assets		26,087
Deferred rent		(1,026)
Deferred rent non-current		(11,052)
Operating lease liabilities		4,930
Non-current operating lease liabilities		$ 32,682

Basis of Presentation and Sig_6

Basis of Presentation and Significant Accounting Policies - Impact of Adopting ASC 842 on Financial Statements (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Deferred rent		$ 1,202
Sublease income	$ 525	$ 176

Property and Equipment, net - S

Property and Equipment, net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 27,217	$ 25,875
Accumulated depreciation	(8,346)	(7,375)
Total property and equipment, net	18,871	18,500
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	592	443
Furniture, Fixtures and Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	2,453	2,453
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	9,571	8,964
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	$ 825	$ 239

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 1	$ 0.8

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Payroll and employee-related costs	$ 3,834	$ 7,321
Research costs	8,023	7,973
Licensing fees	105	625
Professional fees	2,446	1,848
Intellectual property costs	1,101	2,193
Accrued property and equipment	103	294
Other	68	598
Total	$ 15,680	$ 20,852

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Contingencies And Commitments [Line Items]
Research and development expense	[1]	$ 33,822	$ 19,519
Research Agreements [Member]
Contingencies And Commitments [Line Items]
Research and development expense		1,700
Research Agreements [Member] | Scenario Forecast [Member]
Contingencies And Commitments [Line Items]
Research and development expense				$ 1,900	$ 2,100
Manufacturing Agreements [Member] | Prepaid Expenses [Member]
Contingencies And Commitments [Line Items]
Upfront payment recorded as prepaid expense		4,000
Letter of Credit [Member]
Contingencies And Commitments [Line Items]
Letters of credit secured by cash held in restricted depository account		$ 3,200
[1]	Including the following research and development expense with a related party, see Notes 6 & 11:

Leases - Additional Information

Leases - Additional Information (Detail) - ft²	1 Months Ended		3 Months Ended
	May 31, 2016	Jun. 30, 2015	Mar. 31, 2019
2015 Lease [Member]
Lessee Lease Description [Line Items]
Lease commencement date		Nov. 15, 2015
Lease expiration date		Feb. 28, 2022
2016 Sublease [Member]
Lessee Lease Description [Line Items]
Lease commencement date	Dec. 23, 2016
Lease expiration date	Dec. 31, 2026
Lessee, operating sublease, option to extend			an option to extend the term of sublease for an additional five-year period if, at the time of expiration of the initial term
Lessee, operating sublease, existence of option to extend	true
Extended term of lease expiration	5 years
Operating Lease, Research Facility Space [Member]
Lessee Lease Description [Line Items]
Leased space		19,817

Leases - Summary of Lease Asset

Leases - Summary of Lease Assets and Liabilities (Detail) $ in Thousands	Mar. 31, 2019USD ($)
Assets
Operating lease assets	$ 25,098
Total lease assets	25,098
Liabilities
Operating lease liabilities, current	4,899
Operating lease liabilities, net of current portion	31,728
Total lease liabilities	$ 36,627

Leases - Summary of Operating L

Leases - Summary of Operating Lease Costs Included in Research and Development and General and Administrative Expense, as well as Sublease Income (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease costs	$ 1,822
Short-term lease costs	1,138
Variable lease costs	730
Sublease income	(525)	$ (176)
Net lease cost	$ 3,165

Leases - Summary of Maturity of

Leases - Summary of Maturity of Undiscounted Payments Due under Lease Liabilities and Present Value of Those Liabilities (Detail) $ in Thousands	Mar. 31, 2019USD ($)
Leases [Abstract]
2019	$ 6,367
2020	6,866
2021	7,072
2022	5,874
2023	5,855
Thereafter	18,639
Total	50,673
Present value adjustment	(14,046)
Present value of lease liabilities	$ 36,627

Leases - Summary of Lease Term

Leases - Summary of Lease Term and Discount Rate (Detail)	Mar. 31, 2019
Leases [Abstract]
Operating leases, weighted-average remaining lease term (years)	7 years 2 months 12 days
Operating leases, weighted-average discount rate	9.70%

Leases - Summary of Cash Paid f

Leases - Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 1,818
Operating cash flows from operating leases	$ 1,818

Significant Contracts - Additio

Significant Contracts - Additional Information (Detail)		Feb. 12, 2016USD ($)	Oct. 26, 2015USD ($)Milestone	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2016USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue	[1]			$ 328,000	$ 1,358,000
Non-current deferred revenue				57,755,000		$ 57,780,000
Research and development expense	[2]			$ 33,822,000	19,519,000
Date of joint venture agreement				Dec. 19, 2015
Equity method investment							$ 36,500,000
Unrealized equity method losses				$ 1,025,000	1,091,000		$ 36,500,000
Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue				200,000	1,100,000
Research and development expense				$ 500,000	1,100,000
Date of formation of joint venture entity				Feb. 12, 2016
Equity method investment, ownership percentage		50.00%
Cash contribution		$ 100,000
Other payments due to company from joint venture entity		0
Unrealized equity method losses				$ 1,000,000	1,100,000
Net loss of joint venture				14,200,000	12,500,000
Unrecognized equity method losses in excess of Company's interest				51,900,000		$ 45,300,000
License and Service [Member] | Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue		35,000,000
Royalty [Member] | Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue		$ 0
Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Nonrefundable upfront payment received			$ 75,000,000
Milestone payment receivable			420,000,000
Revenue, remaining performance obligation			82,000,000	57,900,000
Non-current deferred revenue				57,800,000
Research and development expense				7,100,000	4,400,000
Reimbursements from research and license agreements				4,500,000	3,100,000
Vertex Pharmaceuticals Inc [Member] | License and Service [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue				100,000	$ 200,000
Vertex Pharmaceuticals Inc [Member] | Research and Development [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Variable consideration received			19,300,000
Vertex Pharmaceuticals Inc [Member] | Joint Development Agreement [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 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.
Vertex Pharmaceuticals Inc [Member] | Non-Exclusive Research License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			500,000
Vertex Pharmaceuticals Inc [Member] | Material Right to Discounts for Exclusive Licenses [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			57,700,000
Vertex Pharmaceuticals Inc [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Unit One [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			22,200,000
Vertex Pharmaceuticals Inc [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Unit Two [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			18,700,000
Vertex Pharmaceuticals Inc [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Unit Three [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			8,400,000
Vertex Pharmaceuticals Inc [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Unit Four [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			8,400,000
Vertex Pharmaceuticals Inc [Member] | Co-exclusive Development and Commercialization Licenses and Research License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			$ 23,800,000
Vertex Pharmaceuticals Inc [Member] | Clinical Development And Regulatory Milestone [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of developmental milestone events | Milestone			9
Vertex Pharmaceuticals Inc [Member] | Clinical Development Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			$ 90,000,000
Vertex Pharmaceuticals Inc [Member] | Regulatory Approval Milestone [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			235,000,000
Vertex Pharmaceuticals Inc [Member] | Commercial Milestones [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
Vertex Pharmaceuticals Inc [Member] | Exercise of Exclusive Option [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			$ 10,000,000
Vertex Pharmaceuticals Inc [Member] | Collaborative Arrangement Copromotion [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			10,000,000
Vertex Pharmaceuticals Inc [Member] | Commercial Milestone Event One [Member] | Minimum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue			500,000,000
Vertex Pharmaceuticals Inc [Member] | Commercial Milestone Event Two [Member] | Minimum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue			$ 1,000,000,000
[1]	Including the following revenue from a related party, see Notes 6 & 11:
[2]	Including the following research and development expense with a related party, see Notes 6 & 11:

Share Capital - Additional Info

Share Capital - Additional Information (Detail)	1 Months Ended		3 Months Ended
	Apr. 29, 2019USD ($)shares	Aug. 31, 2018USD ($)	Mar. 31, 2019USD ($)shares	Mar. 31, 2018USD ($)	Mar. 31, 2019SFr / sharesshares	Dec. 31, 2018SFr / sharesshares
Class of Stock [Line Items]
Common stock, shares authorized					53,325,963	52,183,139
Common shares, par value | SFr / shares					SFr 0.03	SFr 0.03
Treasury stock, shares					307,936	307,936
Capital reserved for future issuance					368,420
Net cash proceeds from sale of common stock | $			$ 23,894,000	$ 122,597,000
Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common stock, shares sold			631,580
Net cash proceeds from sale of common stock | $			$ 23,900,000
Issuance costs | $			$ 700,000
Sales Agreement With Jefferies LLC [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Common stock, shares sold	493,017
Net cash proceeds from sale of common stock | $	$ 18,700,000
Sales Agreement With Jefferies LLC [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds | $		$ 125,000,000
Swiss Law [Member]
Class of Stock [Line Items]
Common stock, shares authorized					17,756,799
Debt Instruments [Member]
Class of Stock [Line Items]
Capital reserved for future issuance					4,919,700
Unvested Restricted Share Award [Member]
Class of Stock [Line Items]
Unvested restricted stock award					13,962
Employee Benefit Plans [Member]
Class of Stock [Line Items]
Capital reserved for future issuance					15,579,296

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 10,696	$ 6,673
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	4,962	2,916
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	4,709	2,666
Loss from Equity Method Investment [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,025	$ 1,091

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Stock Options, Outstanding, Beginning Balance	6,689,311
Stock Options, Granted	1,545,573
Stock Options, Exercised	(148,743)
Stock Options, Cancelled or forfeited	(53,559)
Stock Options, Outstanding, Ending Balance	8,032,582	6,689,311
Stock Options, Exercisable	2,798,109
Stock Options, Vested or expected to vest	8,032,582
Weighted-Average Exercise Price, Outstanding, Beginning Balance	$ 25.42
Weighted-Average Exercise Price, Granted	35.25
Weighted-Average Exercise Price, Exercised	13.35
Weighted-Average Exercise Price, Cancelled or forfeited	39.57
Weighted-Average Exercise Price, Outstanding, Ending Balance	27.44	$ 25.42
Weighted-Average Exercise Price, Exercisable	17.17
Weighted-Average Exercise Price, Vested or expected to vest	$ 27.44
Weighted-Average Remaining Contractual Term	8 years 6 months	8 years 3 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 6 months
Aggregate Intrinsic Value, Outstanding Balance	$ 102,371	$ 68,572
Aggregate Intrinsic Value, Exercisable	58,010
Aggregate Intrinsic Value, Vested or expected to vest	$ 102,371

Stock-based Compensation - Assu

Stock-based Compensation - Assumptions to Estimate Fair Value of Stock Option Award Using the Black-Scholes Option-Pricing Model (Detail)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted-average expected volatility	69.30%	70.50%
Expected term (in years)	6 years	6 years
Risk-free interest rate	2.50%	2.70%
Expected dividend yield	0.00%	0.00%

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock options	$ 107.6
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition	3 years 1 month 6 days
Restricted Common Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition	1 year 7 months 6 days
Total unrecognized compensation expense	$ 9.4

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted Stock [Member]	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock, Unvested Beginning Balance | shares	327,342
Restricted Stock, Granted | shares	40,000
Restricted Stock, Vested | shares	(10,046)
Restricted Stock, Cancelled or forfeited | shares	(12,000)
Restricted Stock, Unvested Ending Balance | shares	345,296
Weighted-Average Grant Date Fair Value, Unvested Beginning Balance | $ / shares	$ 36.72
Weighted-Average Grant Date Fair Value, Granted | $ / shares	32.06
Weighted-Average Grant Date Fair Value, Vested | $ / shares	4.88
Weighted-Average Grant Date Fair Value, Cancelled or forfeited | $ / shares	38.33
Weighted-Average Grant Date Fair Value, Unvested Ending Balance | $ / shares	$ 37.05

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Shareholders - Schedule of Antidilutive Securities Excluded from Calculation of Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of net loss per share	8,377,878	6,785,592
Outstanding Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of net loss per share	8,032,582	6,638,120
Unvested Restricted Common Shares [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of net loss per share	345,296	147,472

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income tax provision	$ 85	$ 86
Effective income tax rate	(0.20%)	(0.30%)

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail)	3 Months Ended
	Dec. 31, 2018
Collaboration Agreement [Member] | Vertex Pharmaceuticals Inc [Member] | Minimum [Member]
Related Party Transaction [Line Items]
Voting interest Percentage	10.00%