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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2017	Aug. 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q2
Trading Symbol	WVE
Entity Registrant Name	WAVE LIFE SCIENCES LTD.
Entity Central Index Key	0001631574
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		27,760,214

Unaudited Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 197,394	$ 150,293
Prepaid expenses and other current assets	3,830	1,483
Deferred tax assets		214
Total current assets	201,224	151,990
Property and equipment, net	20,775	8,607
Deferred tax assets	774	560
Restricted cash	3,606	3,601
Other assets	53	53
Total assets	226,432	164,811
Current liabilities:
Accounts payable	7,983	4,943
Accrued expenses and other current liabilities	4,589	4,434
Current portion of capital lease obligation	47	62
Current portion of deferred revenue	2,705	2,705
Current portion of lease incentive obligation	231	11
Total current liabilities	15,555	12,155
Long-term liabilities:
Capital lease obligation, net of current portion		16
Deferred rent	2,864	680
Deferred revenue, net of current portion	6,959	8,311
Lease incentive obligation, net of current portion	2,197	116
Other liabilities	2,071	796
Total long-term liabilities	14,091	9,919
Total liabilities	29,646	22,074
Series A preferred shares, no par value; 3,901,348 shares issued and outstanding at June 30, 2017 and December 31, 2016	7,874	7,874
Shareholders’ equity:
Ordinary shares, no par value; 27,731,412 and 23,502,169 shares issued and outstanding at June 30, 2017 and December 31, 2016, respectively	309,355	215,602
Additional paid-in capital	15,996	10,029
Accumulated other comprehensive loss	(273)	(291)
Accumulated deficit	(136,166)	(90,477)
Total shareholders’ equity	188,912	134,863
Total liabilities, Series A preferred shares and shareholders’ equity	$ 226,432	$ 164,811

Unaudited Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Series A preferred stock, par value	$ 0	$ 0
Series A preferred stock, shares issued	3,901,348	3,901,348
Series A preferred stock, shares outstanding	3,901,348	3,901,348
Common stock, par value	$ 0	$ 0
Common stock, shares issued	27,731,412	23,502,169
Common stock, shares outstanding	27,731,412	23,502,169

Unaudited Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenue	$ 676	$ 417	$ 1,352	$ 417
Operating expenses:
Research and development	19,103	8,401	33,843	13,137
General and administrative	6,667	3,654	12,517	6,870
Total operating expenses	25,770	12,055	46,360	20,007
Loss from operations	(25,094)	(11,638)	(45,008)	(19,590)
Other income (expense):
Dividend income	482		772
Interest income (expense), net	1	106	4	210
Other income (expense), net	(64)	15	(136)	11
Total other income (expense), net	419	121	640	221
Loss before income tax provision	(24,675)	(11,517)	(44,368)	(19,369)
Income tax provision	(18)	(48)	(1,321)	(43)
Net loss	$ (24,693)	$ (11,565)	$ (45,689)	$ (19,412)
Net loss per share attributable to ordinary shareholders—basic and diluted	$ (0.92)	$ (0.51)	$ (1.81)	$ (0.88)
Weighted-average ordinary shares used in computing net loss per share attributable to ordinary shareholders—basic and diluted	26,899,058	22,708,022	25,224,725	22,126,562

Unaudited Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (24,693)	$ (11,565)	$ (45,689)	$ (19,412)
Other comprehensive income (loss):
Foreign currency translation	3	24	18	35
Comprehensive loss	$ (24,690)	$ (11,541)	$ (45,671)	$ (19,377)

Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities
Net loss	$ (45,689)	$ (19,412)
Adjustments to reconcile net loss to net cash flows used in operating activities:
Amortization of lease incentive obligation	(66)
Depreciation of property and equipment	671	337
Share-based compensation expense	5,966	2,136
Deferred rent	2,184	254
Deferred income taxes		43
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,343)	(2,069)
Accounts payable	1,685	1,183
Accrued expenses and other current liabilities	164	1,208
Deferred revenue	(1,352)	9,583
Other non-current liabilities	1,274	(9)
Net cash used in operating activities	(37,506)	(6,746)
Cash flows from investing activities
Increase in restricted cash	(5)
Proceeds from the sale of property and equipment		4
Purchases of property and equipment	(9,202)	(1,563)
Net cash used in investing activities	(9,207)	(1,559)
Cash flows from financing activities
Proceeds from issuance of ordinary shares, net of offering costs	93,514	30,000
Costs associated with initial public offering		(1,075)
Payments on capital lease obligation	(31)	(31)
Proceeds from the exercise of share options	243	28
Net cash provided by financing activities	93,726	28,922
Effect of foreign exchange rates on cash	88	(72)
Net increase in cash and cash equivalents	47,101	20,545
Cash and cash equivalents at beginning of period	150,293	161,220
Cash and cash equivalents at end of period	197,394	181,765
Supplemental disclosure of cash flow information:
Deferred follow-on offering costs in accrued expenses at period end	5
Property and equipment purchases in accounts payable and accrued expenses at period end	$ 2,987	$ 1,039

The Company	6 Months Ended
The Company	Jun. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company	1. THE COMPANY Organization Wave Life Sciences Ltd. (together with its subsidiaries, “Wave” or the “Company”) is a genetic medicines company with an innovative and proprietary synthetic chemistry drug development platform that the Company is using to design, develop and commercialize a broad pipeline of first-in-class or best-in-class nucleic acid therapeutic candidates for genetically defined diseases. The Company is initially developing oligonucleotides that target genetic defects to either reduce the expression of disease-promoting proteins or transform the production of dysfunctional mutant proteins into the production of functional proteins. The Company was incorporated in Singapore on July 23, 2012 and has its principal U.S. office in Cambridge, Massachusetts. The Company was incorporated with the purpose of combining two commonly held companies, Wave Life Sciences USA, Inc. (“Wave USA”), a Delaware corporation (formerly Ontorii, Inc.), and Wave Life Sciences Japan, Inc. (“Wave Japan”), a company organized under the laws of Japan (formerly Chiralgen., Ltd.), which occurred on September 13, 2012. On May 31, 2016, Wave Life Sciences Ireland Limited (“Wave Ireland”) was formed as a wholly-owned subsidiary of Wave Life Sciences Ltd. On April 3, 2017, Wave Life Sciences UK Limited (“Wave UK”) was formed as a wholly-owned subsidiary of Wave Life Sciences Ltd. Wave UK was formed as a private company organized under the laws of England and Wales. The Company’s primary activities since inception have been developing a synthetic chemistry drug development platform to design, develop and commercialize nucleic acid therapeutic programs, advancing the Company’s neurology franchise, expanding the Company’s research and development activities to enter the clinic, building the Company’s intellectual property, recruiting personnel and raising capital to support these activities. Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, developing internal manufacturing capabilities, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. The Company’s therapeutic programs will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization of any product candidates. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. The Company’s therapeutic programs are currently in the development or discovery stage. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants. Basis of Presentation The Company has prepared the accompanying consolidated financial statements in conformity with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and in U.S. dollars.

Significant Accounting Policies	6 Months Ended
Significant Accounting Policies	Jun. 30, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	2. SIGNIFICANT ACCOUNTING POLICIES The significant accounting policies described in the Company’s audited financial statements as of and for the year ended December 31, 2016, and the notes thereto, which are included in the Company’s 2016 Annual Report on Form 10-K filed with the Securities and Exchange Commission (“SEC”) on March 16, 2017, have had no material changes during the three and six months ended June 30, 2017. Unaudited Interim Financial Data The accompanying interim consolidated balance sheet as of June 30, 2017, the related interim consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2017 and 2016, and cash flows for the six months ended June 30, 2017 and 2016, and the related interim information contained within the notes to the consolidated financial statements have been prepared in accordance with the rules and regulations of the SEC for interim financial information. Accordingly, they do not include all of the information and the notes required by U.S. GAAP for complete financial statements. The financial data and other information disclosed in these notes related to the three and six months ended June 30, 2017 and 2016 are unaudited. In the opinion of management, the unaudited interim consolidated financial statements reflect all adjustments, consisting of normal and recurring adjustments, necessary for the fair presentation of the Company’s financial position and results of operations for the three and six months ended June 30, 2017 and 2016. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the year ending December 31, 2017 or any other interim period or future year or period. Principles of Consolidation The Company’s consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. Recently Issued Accounting Pronouncements The recently issued accounting pronouncements described in the Company’s audited financial statements as of and for the year ended December 31, 2016, and the notes thereto, which are included in the Company’s 2016 Annual Report on Form 10-K filed with the SEC on March 16, 2017, have had no material changes during the three and six months ended June 30, 2017, except as described below. In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. The new standard will be effective on January 1, 2018 and earlier application is permitted only for annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting period. For the year ended December 31, 2016 and the six months ended June 30, 2017, revenue was generated exclusively from the Pfizer Collaboration Agreement. The Company is currently evaluating the potential impact that ASU 2014-09 may have on its financial position and results of operations as it relates to this single arrangement, and expects to elect the modified retrospective application as its transition method. In November 2015, the FASB issued Accounting Standards Update No. 2015-17, Balance Sheet Classification of Deferred Taxes (“ASU 2015-17”), which requires entities to present deferred tax assets and liabilities, along with any related valuation allowance, as noncurrent on the balance sheet. The new standard is effective for annual and interim periods beginning after December 15, 2016. During the three months ended March 31, 2017, the Company elected to adopt ASU 2015-17 on a prospective basis. The adoption of this standard resulted in the reclassification of short-term deferred tax assets to long-term deferred tax assets.

April 2017 Follow-on Underwritten Public Offering	6 Months Ended
April 2017 Follow-on Underwritten Public Offering	Jun. 30, 2017
Equity [Abstract]
April 2017 Follow-on Underwritten Public Offering	3. APRIL 2017 FOLLOW-ON UNDERWRITTEN PUBLIC OFFERING On April 18, 2017, the Company issued and sold in an underwritten public offering (the “Offering”) an aggregate of 4,166,667 ordinary shares at $24.00 per share. The shares were issued pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-215428) that the SEC declared effective on February 6, 2017. A prospectus and prospectus supplement relating to the Offering has been filed with the SEC. The Offering resulted in $93.5 million of net proceeds to the Company, after deducting underwriting discounts and commissions and other offering expenses.

Share-Based Compensation

6 Months Ended

Jun. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

4. SHARE-BASED COMPENSATION

The Wave Life Sciences Ltd. 2014 Equity Incentive Plan (the “2014 Plan”) authorizes the board of directors or a committee of the board to grant incentive share options, non-qualified share options, share appreciation rights and restricted share awards to eligible employees, outside directors and consultants of the Company. Options generally vest over periods of one to four years, and options that lapse or are forfeited are available to be granted again. The contractual life of all options is generally five or ten years from the grant date.

As of June 30, 2017, 692,363 ordinary shares remained available for future grant under the 2014 Plan.

The Company measures and records the value of options granted to non-employees over the period of time that services are provided and, as such, unvested portions are subject to re-measurement at subsequent reporting periods.

Share Options

Share option activity under the 2014 Plan for the six months ended June 30, 2017 is summarized as follows:

	Number of Shares			Weighted- Average Exercise Price
Options outstanding as of January 1, 2017		3,577,766		$	10.58
Granted		360,000		$	26.67
Exercised		(62,576	)	$	3.90
Cancelled or forfeited		(23,844	)	$	20.38
Outstanding as of June 30, 2017		3,851,346		$	12.13
Options exercisable as of June 30, 2017		1,750,269		$	5.46
Options unvested as of June 30, 2017		2,101,077		$	17.68

The Company recorded share-based compensation expense related to options granted to non-employees in the amount of $0.5 million and $0.6 million for the three months ended June 30, 2017 and 2016, respectively. During the six months ended June 30, 2017 and 2016, the Company recorded share-based compensation expense related to options granted to non-employees in the amount of $1.3 million and $1.0 million, respectively. Share-based compensation expense related to non-employees is recorded in research and development expenses.

Restricted Share Units

Restricted share unit (“RSU”) activity for the six months ended June 30, 2017 is summarized as follows:

	RSUs			Average Grant Date Fair Value (in dollars per share)
RSUs Outstanding as of January 1, 2017		22,750		$	21.69
Granted		170,859		$	29.05
Vested		—		$	—
Forfeited		(1,952	)	$	29.05
RSUs Outstanding at June 30, 2017		191,657		$	28.18

The RSUs granted in 2016 fully vest upon the first anniversary of the grant date. The RSUs granted in 2017 vest over a four-year period. Any RSUs that are forfeited or canceled are available to be granted again.

Share-based compensation expense for the three and six months ended June 30, 2017 and 2016 was classified in the consolidated statements of operations as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
	(in thousands)
Research and development expenses	$	1,812	$	922	$	3,768	$	1,510
General and administrative expenses		1,156		348		2,198		626
Total share-based compensation	$	2,968	$	1,270	$	5,966	$	2,136

Pfizer Collaboration and Share Purchase Agreement	6 Months Ended
Pfizer Collaboration and Share Purchase Agreement	Jun. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Pfizer Collaboration and Share Purchase Agreement	5. PFIZER COLLABORATION AND SHARE PURCHASE AGREEMENT On May 5, 2016, the Company entered into a Research, License and Option Agreement (the “Pfizer Collaboration Agreement”) with Pfizer Inc. (“Pfizer”). Pursuant to the terms of the Pfizer Collaboration Agreement, the Company and Pfizer agreed to collaborate on the discovery, development and commercialization of stereopure oligonucleotide therapeutics for up to five programs (the “Pfizer Programs”), each directed at a genetically-defined hepatic target selected by Pfizer (the “Collaboration”). The Company received $10.0 million as an upfront license fee under the Pfizer Collaboration Agreement. Subject to option exercises by Pfizer, assuming five potential products are successfully developed and commercialized, the Company may earn up to $871.0 million in potential research, development and commercial milestone payments, plus royalties, tiered up to low double-digits, on sales of any products that may result from the Collaboration. None of the payments under the Pfizer Collaboration Agreement are refundable. Simultaneously with the entry into the Pfizer Collaboration Agreement, the Company entered into a Share Purchase Agreement (the “Pfizer Equity Agreement,” and together with the Pfizer Collaboration Agreement, the “Pfizer Agreements”) with C.P. Pharmaceuticals International C.V., an affiliate of Pfizer (the “Pfizer Affiliate”). Pursuant to the terms of the Pfizer Equity Agreement, the Pfizer Affiliate purchased 1,875,000 of the Company’s ordinary shares (the “Shares”) at a purchase price of $16.00 per share, for an aggregate purchase price of $30.0 million. The Company did not incur any material costs in connection with the issuance of the Shares. Under the Pfizer Collaboration Agreement, the parties agreed to collaborate during the four-year Research Term. During the Research Term, the Company is responsible to use its commercially reasonable efforts to advance up to five programs through to the selection of clinical candidates. At that stage, Pfizer may elect to license any of these Pfizer Programs exclusively and to have exclusive rights to undertake the clinical development of the resulting clinical candidates into products and the potential commercialization of any such products thereafter. In addition, the Company receives a non-exclusive, royalty-bearing sublicensable license to use Pfizer’s hepatic targeting technology in any of the Company’s own hepatic programs that are outside the scope of the Collaboration (the “Wave Programs”). If the Company uses this technology on the Wave Programs, Pfizer is eligible to receive potential development and commercial milestone payments from the Company. Pfizer is also eligible to receive tiered royalties on sales of any products that include Pfizer’s hepatic targeting technology. Pfizer nominated two hepatic targets upon entry into the Collaboration in May 2016. In August 2016, Pfizer nominated the third hepatic target under the Collaboration and has the option to nominate two additional targets by November 5, 2017. The Collaboration is managed by a joint steering committee in which both parties are represented equally, which will oversee the scientific progression of each Pfizer Program up to the clinical candidate stage. During the four-year Research Term and for a period of two years thereafter, the Company has agreed to work exclusively with Pfizer with respect to using any of the Company’s stereopure oligonucleotide technology that is specific for the applicable hepatic target which is the basis of any Pfizer Program. The stated term of the Pfizer Collaboration Agreement commenced on May 5, 2016 and terminates, with respect to each Pfizer Program, on the date of the last to expire payment obligations and expires, with respect to each Wave Program, on a program-by-program basis accordingly. Pfizer may terminate its rights related to a Pfizer Program under the Pfizer Collaboration Agreement at its own convenience upon 90 days’ notice to the Company. The Company may also terminate its rights related to a Wave Program at its own convenience upon 90 days’ notice to Pfizer. The Pfizer Collaboration Agreement may also be terminated by either party in the event of an uncured material breach of the Pfizer Collaboration Agreement by the other party. During the three and six months ended June 30, 2017, the Company recognized revenue of $0.7 million and $1.4 million, respectively, under the Pfizer Collaboration Agreement. During the three and six months ended June 30, 2016, the Company recognized revenue of $0.4 million under the Pfizer Collaboration Agreement. Deferred revenue amounted to $9.7 million at June 30, 2017, of which $2.7 million is included in current liabilities.

Net Loss Per Ordinary Share

6 Months Ended

Jun. 30, 2017

Earnings Per Share [Abstract]

Net Loss Per Ordinary Share

6. NET LOSS PER ORDINARY SHARE

The Company applies the two-class method to calculate its basic and diluted net loss per share attributable to ordinary shareholders, as its Series A preferred shares are participating securities. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to ordinary shareholders. However, for the periods presented, the two-class method does not impact the net loss per ordinary share as the Company was in a net loss position for each of the periods presented and holders of Series A preferred shares do not participate in losses.

Basic loss per share is computed by dividing net loss attributable to ordinary shareholders by the weighted-average number of ordinary shares used in computing net loss per share attributable to ordinary shareholders.

The Company’s potentially dilutive shares, which include outstanding share options to purchase ordinary shares and Series A preferred shares, are considered to be ordinary share equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive.

The following ordinary share equivalents, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to ordinary shareholders for the periods indicated because including them would have had an anti-dilutive effect:

	As of June 30,
	2017		2016
Options to purchase ordinary shares		3,851,346		3,152,926
Restricted share units		191,657		—
Series A preferred shares		3,901,348		3,901,348

Income Taxes	6 Months Ended
Income Taxes	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	7. INCOME TAXES The Company is a multi-national company subject to taxation in the United States and various other jurisdictions. During the three months ended June 30, 2017 and 2016, the Company recorded a tax provision of less than $0.1 million and less than $0.1 million, respectively, both of which are primarily the result of U.S. income generated under research and management services arrangements between the Company’s U.S. and Singapore entities. During the six months ended June 30, 2017 and 2016, the Company recorded a tax provision of $1.3 million and less than $0.1 million, respectively. The increase in the tax provision for the six months ended June 30, 2017 as compared to the six months ended June 30, 2016, is a result of additional income earned in the United States under the aforementioned research and management services arrangements between the Company’s U.S. and Singapore entities. During the three and six months ended June 30, 2017 and 2016, the Company recorded no income tax benefits for the net operating losses incurred in Japan, Singapore, or the United Kingdom, due to its uncertainty of realizing a benefit from those items. The Company’s reserves related to taxes and its accounting for uncertain tax positions are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more-likely-than-not to be realized following resolution of any potential contingencies present related to the tax benefit.

Related Parties

6 Months Ended

Jun. 30, 2017

Related Parties

8. RELATED PARTIES

The Company had the following related party transactions for the periods presented in the accompanying consolidated financial statements, which have not otherwise been discussed in these notes to the consolidated financial statements:

•

The Company had cash of $116 thousand and $118 thousand at June 30, 2017 and December 31, 2016, respectively, in depository accounts with Kagoshima Bank, Ltd., an affiliate of one of the Company’s shareholders, Kagoshima Shinsangyo Sousei Investment Limited Partnership.

•

Pursuant to the terms of various service agreements with Shin Nippon Biomedical Laboratories Ltd. (“SNBL”), one of the Company’s shareholders, the Company paid SNBL $73 thousand and $210 thousand during the three months ended June 30, 2017 and 2016, respectively, and $78 thousand and $325 thousand during the six months ended June 30, 2017 and 2016, respectively, for contract research services provided to the Company and its affiliates.

•

In 2012, the Company entered into a consulting agreement for scientific advisory services with Dr. Gregory L. Verdine, one of the Company’s founders and the Chairman of the Company’s Board of Directors. The consulting agreement does not have a specific term and may be terminated by either party upon 14 days’ prior written notice. Pursuant to the consulting agreement, the Company pays Dr. Verdine approximately $13 thousand per month, plus reimbursement of certain expenses.

Geographic Data

6 Months Ended

Jun. 30, 2017

Text Block [Abstract]

Geographic Data

9. GEOGRAPHIC DATA

The Company’s long-lived assets consist of property and equipment and are located in the following geographical areas:

	June 30, 2017		December 31, 2016
	(in thousands)
Asia	$	60	$	136
United States		20,715		8,471
Total long-lived assets	$	20,775	$	8,607

Significant Accounting Policies (Policies)	6 Months Ended
Significant Accounting Policies (Policies)	Jun. 30, 2017
Accounting Policies [Abstract]
Unaudited Interim Financial Data	Unaudited Interim Financial Data The accompanying interim consolidated balance sheet as of June 30, 2017, the related interim consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2017 and 2016, and cash flows for the six months ended June 30, 2017 and 2016, and the related interim information contained within the notes to the consolidated financial statements have been prepared in accordance with the rules and regulations of the SEC for interim financial information. Accordingly, they do not include all of the information and the notes required by U.S. GAAP for complete financial statements. The financial data and other information disclosed in these notes related to the three and six months ended June 30, 2017 and 2016 are unaudited. In the opinion of management, the unaudited interim consolidated financial statements reflect all adjustments, consisting of normal and recurring adjustments, necessary for the fair presentation of the Company’s financial position and results of operations for the three and six months ended June 30, 2017 and 2016. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the year ending December 31, 2017 or any other interim period or future year or period.
Principles of Consolidation	Principles of Consolidation The Company’s consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements The recently issued accounting pronouncements described in the Company’s audited financial statements as of and for the year ended December 31, 2016, and the notes thereto, which are included in the Company’s 2016 Annual Report on Form 10-K filed with the SEC on March 16, 2017, have had no material changes during the three and six months ended June 30, 2017, except as described below. In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. The new standard will be effective on January 1, 2018 and earlier application is permitted only for annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting period. For the year ended December 31, 2016 and the six months ended June 30, 2017, revenue was generated exclusively from the Pfizer Collaboration Agreement. The Company is currently evaluating the potential impact that ASU 2014-09 may have on its financial position and results of operations as it relates to this single arrangement, and expects to elect the modified retrospective application as its transition method. In November 2015, the FASB issued Accounting Standards Update No. 2015-17, Balance Sheet Classification of Deferred Taxes (“ASU 2015-17”), which requires entities to present deferred tax assets and liabilities, along with any related valuation allowance, as noncurrent on the balance sheet. The new standard is effective for annual and interim periods beginning after December 15, 2016. During the three months ended March 31, 2017, the Company elected to adopt ASU 2015-17 on a prospective basis. The adoption of this standard resulted in the reclassification of short-term deferred tax assets to long-term deferred tax assets.

Share-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Share Option Activity

Share Options

Share option activity under the 2014 Plan for the six months ended June 30, 2017 is summarized as follows:

	Number of Shares			Weighted- Average Exercise Price
Options outstanding as of January 1, 2017		3,577,766		$	10.58
Granted		360,000		$	26.67
Exercised		(62,576	)	$	3.90
Cancelled or forfeited		(23,844	)	$	20.38
Outstanding as of June 30, 2017		3,851,346		$	12.13
Options exercisable as of June 30, 2017		1,750,269		$	5.46
Options unvested as of June 30, 2017		2,101,077		$	17.68

Summary of Restricted Share Units ("RSU") Activity

Restricted Share Units

Restricted share unit (“RSU”) activity for the six months ended June 30, 2017 is summarized as follows:

	RSUs			Average Grant Date Fair Value (in dollars per share)
RSUs Outstanding as of January 1, 2017		22,750		$	21.69
Granted		170,859		$	29.05
Vested		—		$	—
Forfeited		(1,952	)	$	29.05
RSUs Outstanding at June 30, 2017		191,657		$	28.18

Summary of Share-based Compensation Expense Classified in Consolidated Statements of Operations

Share-based compensation expense for the three and six months ended June 30, 2017 and 2016 was classified in the consolidated statements of operations as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
	(in thousands)
Research and development expenses	$	1,812	$	922	$	3,768	$	1,510
General and administrative expenses		1,156		348		2,198		626
Total share-based compensation	$	2,968	$	1,270	$	5,966	$	2,136

Net Loss Per Ordinary Share (Tables)

6 Months Ended

Jun. 30, 2017

Earnings Per Share [Abstract]

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

	As of June 30,
	2017		2016
Options to purchase ordinary shares		3,851,346		3,152,926
Restricted share units		191,657		—
Series A preferred shares		3,901,348		3,901,348

Geographic Data (Tables)

6 Months Ended

Jun. 30, 2017

Text Block [Abstract]

Summary of Long-Lived Assets by Geographical Areas

The Company’s long-lived assets consist of property and equipment and are located in the following geographical areas:

	June 30, 2017		December 31, 2016
	(in thousands)
Asia	$	60	$	136
United States		20,715		8,471
Total long-lived assets	$	20,775	$	8,607

April 2017 Follow-on Underwritten Public Offering - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended
	Apr. 18, 2017	Jun. 30, 2017	Jun. 30, 2016
Subsidiary Sale Of Stock [Line Items]
Net proceeds from sale of ordinary shares		$ 93,514	$ 30,000
April 2017 Follow-on Underwritten Public Offering [Member]
Subsidiary Sale Of Stock [Line Items]
Number of ordinary shares issued and sold	4,166,667
Number of ordinary shares issued and sold, price per share	$ 24.00
Net proceeds from sale of ordinary shares	$ 93,500

Share-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 2,968	$ 1,270	$ 5,966	$ 2,136
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ordinary shares available for future grant	692,363		692,363
2014 Plan [Member] \| Non-Employees Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 500	$ 600	$ 1,300	$ 1,000
2014 Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year
Contractual life of options			5 years
2014 Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Contractual life of options			10 years

Share-Based Compensation - Summary of Share Option Activity (Detail) - 2014 Plan [Member]	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, Number of Shares, Beginning Balance \| shares	3,577,766
Granted, Number of Shares \| shares	360,000
Exercised, Number of Shares \| shares	(62,576)
Cancelled or forfeited, Number of Shares \| shares	(23,844)
Options outstanding, Number of Shares, Ending Balance \| shares	3,851,346
Options exercisable, Number of Shares \| shares	1,750,269
Options unvested, Number of Shares \| shares	2,101,077
Options outstanding, Weighted Average Exercise Price, Beginning Balance \| $ / shares	$ 10.58
Granted, Weighted Average Exercise Price \| $ / shares	26.67
Exercised, Weighted Average Exercise Price \| $ / shares	3.90
Cancelled or forfeited, Weighted Average Exercise Price \| $ / shares	20.38
Option outstanding, Weighted Average Exercise Price, Ending Balance \| $ / shares	12.13
Options exercisable, Weighted Average Exercise Price \| $ / shares	5.46
Options unvested, Weighted Average Exercise Price \| $ / shares	$ 17.68

Share-Based Compensation - Summary of Restricted Stock Units ("RSU") Activity (Detail) - Restricted Share Units [Member]	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Number of Shares, Beginning Balance \| shares	22,750
Granted, Number of Shares \| shares	170,859
Forfeited, Number of Shares \| shares	(1,952)
Outstanding, Number of Shares, Ending Balance \| shares	191,657
Outstanding, Average Grant Date Fair Value, Beginning Balance \| $ / shares	$ 21.69
Granted, Average Grant Date Fair Value \| $ / shares	29.05
Forfeited, Average Grant Date Fair Value \| $ / shares	29.05
Outstanding, Average Grant Date Fair Value, Ending Balance \| $ / shares	$ 28.18

Share-Based Compensation - Summary of Share-based Compensation Expense Classified in Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation	$ 2,968	$ 1,270	$ 5,966	$ 2,136
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation	1,812	922	3,768	1,510
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation	$ 1,156	$ 348	$ 2,198	$ 626

Pfizer Collaboration and Share Purchase Agreement - Additional Information (Detail)		3 Months Ended		6 Months Ended
	May 05, 2016 USD ($) Program Product $ / shares shares	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Current portion of deferred revenue		$ 2,705,000		$ 2,705,000		$ 2,705,000
Pfizer Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of research programs, counterparty nomination \| Program	5
Research term, description				Under the Pfizer Collaboration Agreement, the parties agreed to collaborate during the four-year Research Term. During the Research Term, the Company is responsible to use its commercially reasonable efforts to advance up to five programs through to the selection of clinical candidates. At that stage, Pfizer may elect to license any of these Pfizer Programs exclusively and to have exclusive rights to undertake the clinical development of the resulting clinical candidates into products and the potential commercialization of any such products thereafter.
Collaboration agreement, additional period after research program	2 years
Revenue recognized		700,000	$ 400,000	$ 1,400,000	$ 400,000
Deferred revenue		9,700,000		9,700,000
Current portion of deferred revenue		$ 2,700,000		$ 2,700,000
Maximum [Member] \| Pfizer Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Expected earnings from milestone payments under research program	$ 871,000,000
Research, License and Option Agreement [Member] \| Pfizer Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront amount related to research and development services	$ 10,000,000
Number of potential products are successfully developed and commercialized \| Product	5
Collaboration agreement refundable	$ 0
Shares issued under equity agreement \| shares	1,875,000
Equity investment aggregate purchase price	$ 30,000,000
Purchase price per share \| $ / shares	$ 16.00
Collaborative agreement research term	4 years
Collaboration agreement termination period	90 days

Net Loss Per Ordinary Share - Anti-Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Ordinary Share (Detail) - shares	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Series A Preferred Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	3,901,348	3,901,348
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	3,851,346	3,152,926
Restricted Share Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	191,657

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Taxes [Line Items]
Income tax benefit (provision)	$ (18,000)	$ (48,000)	$ (1,321,000)	$ (43,000)
United States [Member] \| Research and Management Services Arrangements
Income Taxes [Line Items]
Income tax benefit (provision)			(1,300,000)
United States [Member] \| Research and Management Services Arrangements \| Maximum [Member]
Income Taxes [Line Items]
Income tax benefit (provision)	(100,000)	(100,000)		(100,000)
Japan [Member]
Income Taxes [Line Items]
Income tax benefit (provision)	0	0	0	0
Singapore [Member]
Income Taxes [Line Items]
Income tax benefit (provision)	0	0	0	0
United Kingdom [Member]
Income Taxes [Line Items]
Income tax benefit (provision)	$ 0	$ 0	$ 0	$ 0

Related Parties - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Third-Party Investor [Member]
Related Party Transaction [Line Items]
Related party transaction amount			$ 116		$ 118
Shin Nippon Biomedical Laboratories Ltd. (“SNBL”) [Member]
Related Party Transaction [Line Items]
Payment for contract research services	$ 73	$ 210	$ 78	$ 325
Scientific Advisor [Member] \| Consulting Agreement [Member]
Related Party Transaction [Line Items]
Consulting agreement termination notice period			14 days
Consulting service expenses			$ 13

Geographic Data - Summary of Long-Lived Assets by Geographical Areas (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Geographic Area Information [Line Items]
Property and equipment	$ 20,775	$ 8,607
Asia [Member]
Geographic Area Information [Line Items]
Property and equipment	60	136
United States [Member]
Geographic Area Information [Line Items]
Property and equipment	$ 20,715	$ 8,471