Seres Therapeutics (MCRB) 10-Q 2 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 26, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Trading Symbol	MCRB
Entity Registrant Name	Seres Therapeutics, Inc.
Entity Central Index Key	1,609,809
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		40,795,663

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 57,960	$ 36,088
Investments	38,106	113,895
Prepaid expenses and other current assets	5,471	5,095
Total current assets	101,537	155,078
Property and equipment, net	29,904	32,931
Restricted cash	1,513	1,513
Total assets	132,954	189,522
Current liabilities:
Accounts payable	5,158	7,033
Accrued expenses and other current liabilities	13,651	12,513
Deferred revenue - related party	17,962	12,079
Total current liabilities	36,771	31,625
Lease incentive obligation, net of current portion	8,119	8,989
Deferred Rent	2,231	2,233
Deferred revenue, net of current portion - related party	97,959	84,847
Other long-term liabilities	1,129	1,129
Total liabilities	146,209	128,823
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at June 30, 2018 and December 31, 2017; no shares issued and outstanding at June 30, 2018 and December 31, 2017
Common stock, $0.001 par value; 200,000,000 shares authorized at June 30, 2018 and December 31, 2017; 40,754,681 and 40,571,015 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively	40	40
Additional paid-in capital	332,870	324,376
Accumulated other comprehensive loss	(29)	(146)
Accumulated deficit	(346,136)	(263,571)
Total stockholders’ equity/(deficit)	(13,255)	60,699
Total liabilities and stockholders’ equity	$ 132,954	$ 189,522

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	40,754,681	40,571,015
Common stock, shares outstanding	40,754,681	40,571,015

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Total revenue	$ 4,612	$ 3,014	$ 8,583	$ 6,029
Operating expenses:
Research and development expenses	24,053	23,060	47,513	43,203
General and administrative expenses	8,695	8,370	17,472	17,132
Total operating expenses	32,748	31,430	64,985	60,335
Loss from operations	(28,136)	(28,416)	(56,402)	(54,306)
Other income (expense):
Interest income	349	615	696	1,390
Other income (expense)		(217)		(576)
Total other income, net	349	398	696	814
Net loss	$ (27,787)	$ (28,018)	$ (55,706)	$ (53,492)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.68)	$ (0.69)	$ (1.37)	$ (1.32)
Weighted average common shares outstanding, basic and diluted	40,661,464	40,394,605	40,645,040	40,381,643
Other comprehensive (loss) income:
Unrealized (loss) gain on investments, net of tax of $0	$ 77	$ (25)	$ 117	$ (27)
Total other comprehensive (loss) income	77	(25)	117	(27)
Comprehensive loss	(27,710)	(28,043)	(55,589)	(53,519)
Collaboration Revenue - Related Party [Member]
Revenue:
Total revenue	4,271	$ 3,014	8,037	$ 6,029
Grant Revenue [Member]
Revenue:
Total revenue	$ 341		$ 546

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Unrealized (loss) gain on investment, tax	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net loss	$ (55,706)	$ (53,492)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	8,570	8,781
Depreciation and amortization expense	3,895	3,490
Non-cash interest expense		2
Accretion of discount on investments	(132)	(116)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(376)	287
Deferred revenue	(7,863)	(6,029)
Accounts payable	(1,537)	(3,651)
Accrued expenses and other current liabilities	712	(577)
Net cash (used in) operating activities	(52,437)	(51,305)
Cash flows from investing activities:
Purchases of property and equipment	(1,655)	(3,527)
Purchases of investments	(15,456)	(43,795)
Sales and maturities of investments	91,495	77,807
Net cash provided by investing activities	74,384	30,485
Cash flows from financing activities:
Proceeds from exercise of stock options	96	36
Proceeds from issuance of common stock and restricted common stock	26
Payments of employee tax obligations related to vesting of restricted stock units	(197)
Net cash (used in) provided by financing activities	(75)	36
Net increase (decrease) in cash and cash equivalents	21,872	(20,784)
Cash, cash equivalents and restricted cash at beginning of period	37,601	55,939
Cash, cash equivalents and restricted cash at end of period	59,473	35,155
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued expenses	$ 90	$ 140

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Seres Therapeutics, Inc. (the “Company”) was incorporated under the laws of the State of Delaware in October 2010 under the name Newco LS21, Inc. In October 2011, the Company changed its name to Seres Health, Inc., and in May 2015, the Company changed its name to Seres Therapeutics, Inc. The Company is a microbiome therapeutics platform company developing a novel class of biological drugs, which are designed to restore health by repairing the function of a dysbiotic microbiome. The Company’s lead product candidate, SER-109, is designed to reduce recurrences of Clostridium difficile infection (“CDI”), a debilitating infection of the colon, and, if approved by the U.S. Food and Drug Administration (“FDA”), could be a first-in-field oral microbiome drug. The Company’s second product candidate, SER-287, is being developed to treat inflammatory bowel disease (“IBD”) including ulcerative colitis (“UC”). The Company is also developing SER-401, a microbiome therapeutic candidate for use with checkpoint inhibitors (“CPI’s”) in patients with solid tumors. In addition, using its microbiome therapeutics platform, the Company is developing product candidates to treat diseases where the microbiome is implicated, including SER-262, a rationally designed product candidate, to prevent an initial recurrence of primary CDI, SER-301, a rationally designed IBD product candidate, and SER-155, a rationally designed product candidate to prevent infections and improve gastrointestinal barrier function (including the consequences of graft versus host disease) in patients following allogeneic hematopoietic stem cell transplants or solid organ transplants. The Company is also using its microbiome therapeutics platform to conduct research on various indications, including: infectious diseases, metabolic diseases, and inflammatory and immune diseases, including immuno-oncology. 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, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive pre-clinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. The Company’s product candidates are in development. 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. Under Accounting Standards Update, or ASU, 2014-15, Presentation of Financial Statements—Going Concern As of June 30, 2018, the Company had an accumulated deficit of $346.1 million and cash, cash equivalents and short-term investments of $96.1 million. Management has assessed the Company’s ability to continue as a going concern in accordance with the requirements of ASC 205-40 and determined that the Company’s accumulated deficit, history of losses, and future expected losses meet the ASC 205-40 standard for raising substantial doubt about the Company’s ability to continue as a going concern within one year of the issuance date of these condensed consolidated financial statements. The Company’s current financial resources and currently forecasted operating plan would allow the Company to operate into the second quarter of 2019 which is within one year from the issuance of these condensed consolidated financial statements. The Company has developed plans to mitigate this risk, which primarily consist of raising additional capital through some combination of equity or debt financings, and/or potentially new collaborations and reducing cash expenditures. If the Company is not able to secure adequate additional funding, the Company plans to make reductions in spending. In that event, the Company may have to delay, scale back, or eliminate some or all of the Company’s planned clinical trials. The actions necessary to reduce spending under this plan at a level that mitigates the factors described above is not considered probable, as defined in the accounting standards; as such, under the requirements of ASC 205-40, the full extent to which management may extend the Company’s funds through these actions may not be considered in management’s assessment of the Company’s ability to continue as a going concern for the next 12 months as defined by ASC-205-40. As a result, in accordance with the requirements of ASC 205-40, management has concluded that it is required to disclose that substantial doubt exists about the Company’s ability to continue as a going concern for one year from the date these financial statements are issued. The Company is eligible to receive contingent milestone payments under its license and collaboration agreement with Nestec Ltd. (“NHS”), an affiliate of Nestlé Health Science US Holdings, Inc. (“Nestlé Health Science”), a significant stockholder of the Company, if certain development milestones are achieved. However, these milestones are uncertain and there is no assurance that the Company will receive any of them. Until such time, if ever, as the Company can generate substantial product revenue, the Company will finance its cash needs through a combination of public or private equity offerings, debt financings, governmental funding, collaborations, strategic partnerships or marketing, distribution or licensing arrangements with third parties. The Company may not be able to obtain funding on acceptable terms, or at all. If the Company is unable to raise additional funds as and when needed, it would have a negative impact on the Company’s financial condition, which may require the Company to delay, reduce or eliminate certain research and development activities and reduce or eliminate discretionary operating expenses, which could constrain the Company’s ability to pursue its business strategies. Unaudited Interim Financial Information The accompanying unaudited condensed consolidated financial statements as of June 30, 2018 and for the three and six months ended June 30, 2018 and 2017 The unaudited interim financial statements have been prepared on the same basis as the audited consolidated financial statements. The condensed consolidated balance sheet at December 31, 2017 was derived from audited annual financial statements, but does not contain all of the footnote disclosures from the annual financial statements. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments which are necessary for a fair presentation of the Company’s financial position as of June 30, 2018 and consolidated results of operations for the three and six months ended June 30, 2018 and 2017 and its cash flows for the six months ended June 30, 2018 and 2017. Such adjustments are of a normal and recurring nature. The results of operations for the three and six months ended June 30, 2018 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2018.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The significant accounting policies and estimates used in preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2017, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K. There have been no material changes to the Company’s significant accounting policies during the six months ended June 30, 2018 except for the adoption of the new revenue standard discussed in Note 8, Collaboration Revenue. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. Net Loss per Share Basic net loss per share is computed using the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed using the sum of the weighted average number of common shares outstanding during the period and, if dilutive, the weighted average number of potential shares of common stock, including the assumed exercise of stock options and warrants and unvested restricted stock. The restricted stock units granted by the Company entitle the holder of such awards to dividends declared or paid by the board of directors, regardless of whether such awards are unvested, as if such shares were outstanding common shares at the time of the dividend. However, the unvested restricted stock units are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three and Six Months Ended June 30, 2018 2017 Stock options to purchase common stock 7,481,478 6,314,838 Unvested restricted stock units 289,248 408,400 7,770,726 6,723,238 Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board (the “FASB”) issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers The Company has adopted this standard as of the required effective date of January 1, 2018, In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Leases (Topic 842) In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU 2016-18, Restricted Cash The Company’s statements of cash flows includes restricted cash with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on such statements. A reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows is as follows: June 30, December June 30, December 2018 2017 2017 2016 Cash and cash equivalents $ 57,960 $ 36,088 $ 33,642 $ 54,539 Restricted cash 1,513 1,513 1,513 1,400 Total cash, cash equivalents and restricted cash as shown in the statement of cash flows $ 59,473 $ 37,601 $ 35,155 $ 55,939 In June 2018, the FASB issued ASU 2018-07, “Compensation – Stock Compensation (Topic 718).” ASU 2018-07 simplifies the accounting for nonemployee share-based payment transactions. This ASU is effective for public entities for interim and annual reporting periods beginning after December 15, 2018. The Company is currently in the process of evaluating the impact of the guidance on its consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above. The Company’s investments in certificates of deposit are carried at amortized cost, which approximates fair value. Certain cash equivalents or investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The following table presents information about the Company’s assets as of June 30, 2018 and December 31, 2017 that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (note there were no liabilities measured at fair value on a recurring basis in either of the periods presented): Fair Value Measurements as of June 30, 2018 Using: Level 1 Level 2 Level 3 Not Subject to Leveling (1) Total Assets: Cash Equivalents $ — $ 2,992 $ — $ 44,306 $ 47,298 Investments: Commercial Paper $ — $ 10,717 $ — $ — $ 10,717 Certificates of Deposit — 3,430 — — 3,430 Corporate Bonds — 6,744 — — 6,744 Government Securities — 3,746 — — 3,746 Treasury Bonds — 13,469 — — 13,469 $ — $ 41,098 $ — $ 44,306 $ 85,404 (1) Fair Value Measurements as of December 31, 2017 Using: Level 1 Level 2 Level 3 Not Subject to Leveling (1) Total Assets: Cash Equivalents $ — $ — $ — $ 25,964 $ 25,964 Investments: Commercial Paper $ — $ 6,198 $ — $ — $ 6,198 Certificates of Deposit — 8,916 8,916 Corporate Bonds — 58,865 — — 58,865 Government Securities — 22,954 — — 22,954 Treasury Bonds — 16,962 — — 16,962 $ — $ 113,895 $ — $ 25,964 $ 139,859 (1) As of June 30, 2018, the Company’s cash equivalents, which were invested in money market funds and corporate bonds with original maturities of less than 90 days from the date of purchase, were valued based on Level 2 inputs. As of December 31, 2017, the Company’s cash equivalents consisted of money market funds and corporate bonds with original maturities of less than 90 days from the date of purchase and were valued based on Level 2 inputs. The fair value of the Company’s investments, which consisted of commercial paper, certificates of deposit, corporate bonds, government securities and treasury bonds as of June 30, 2018 and December 31, 2017 were determined using Level 2 inputs. During the six months ended June 30, 2018, there were no transfers between Level 1, Level 2 and Level 3.

Investments

Investments	6 Months Ended
	Jun. 30, 2018
Investments Debt And Equity Securities [Abstract]
Investments	4. Investments As of June 30, 2018 and December 31, 2017, the fair value of available-for-sale investments by type of security was as follows: June 30, 2018 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Commercial Paper $ 10,717 $ — $ — $ 10,717 Certificates of Deposit 3,430 — — 3,430 Corporate Bonds 6,754 — (10 ) 6,744 Government Securities 3,747 — (1 ) 3,746 Treasury Bonds 13,486 — (17 ) 13,469 $ 38,134 $ — (28 ) $ 38,106 December 31, 2017 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Commercial Paper $ 6,198 $ — $ — $ 6,198 Certificates of Deposit 8,916 — — 8,916 Corporate Bonds 58,937 — (72 ) 58,865 Government Securities 22,997 — (43 ) 22,954 Treasury Bonds 16,992 — (30 ) 16,962 $ 114,040 $ — $ (145 ) $ 113,895 Investments with original maturities of less than 90 days are included in cash and cash equivalents on the consolidated balance sheets and are not included in the table above. Investments with maturities of less than 12 months are considered current and those investments with maturities greater than 12 months are considered non-current. All investments with unrealized losses at June 30, 2018 have been in a loss position for less than 12 months or the loss is not material and temporary in nature. The Company does not intend to sell the investments that are in an unrealized loss position before recovery of their amortized cost basis.

Property and Equipment, Net

Property and Equipment, Net	6 Months Ended
	Jun. 30, 2018
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consisted of the following: June 30, 2018 December 31, 2017 Laboratory equipment $ 13,988 13,181 Computer equipment 2,852 2,832 Furniture and office equipment 1,033 1,033 Leasehold improvements 27,977 27,963 Construction in progress 388 361 46,238 45,370 Less: Accumulated depreciation and amortization $ (16,334 ) $ (12,439 ) $ 29,904 $ 32,931 Depreciation and amortization expense was $1,954, $ 3,895, $1,760 and $3,490 for the three and six months ended June 30, 2018 and 2017, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	6 Months Ended
	Jun. 30, 2018
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: June 30, 2018 December 31, 2017 Development and manufacturing costs $ 7,163 $ 3,910 Payroll and payroll-related costs 3,132 4,962 Professional fees 455 344 Facility and other 2,901 3,297 $ 13,651 $ 12,513

Stockholders' Equity Common Sto

Stockholders' Equity Common Stock	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Stockholders' Equity Common Stock	7 . Stockholders’ Equity Common Stock Stock Options The following table summarizes the Company’s stock option activity since December 31, 2017: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding as of December 31, 2017 6,125,692 $ 13.00 7.70 $ 15,808 Granted 1,732,276 10.16 Exercised (140,066 ) 0.68 Forfeited (236,424 ) 16.95 Outstanding as of June 30, 2018 7,481,478 $ 12.45 7.75 $ 11,509 Options vested and expected to vest as of June 30, 2018 7,481,478 12.45 7.75 11,509 Options exercisable as of June 30, 2018 3,987,920 $ 11.87 6.78 $ 11,390 The weighted average grant-date fair value of stock options granted during the three and six months ended June 30, 2018 and 2017 was $6.89, $5.82, $7.44 and $6.98 per share, respectively. Restricted Stock The Company has granted restricted stock units with time-based vesting conditions. The table below summarizes the Company’s restricted stock unit activity since December 31, 2017: Number of Shares Weighted Average Grant Date Fair Value Unvested restricted stock units as of December 31, 2017 356,778 $ 10.01 Granted — $ — Forfeited (6,030 ) $ 9.78 Vested (61,500 ) $ 10.12 Unvested restricted stock units as of June 30, 2018 289,248 $ 10.00 Stock-based Compensation Expense The Company recorded stock-based compensation expense related to stock options, restricted stock units and ESPP plan in the following expense categories of its condensed consolidated statements of operations and comprehensive loss: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Research and development expenses $ 2,262 $ 2,094 $ 4,190 $ 3,967 General and administrative expenses 2,072 2,409 4,380 4,814 $ 4,334 $ 4,503 $ 8,570 $ 8,781 Employee Stock Purchase Plan The Company’s Employee Stock Purchase Plan (“ESPP”) provides that eligible employees may contribute up to 15% of their eligible earnings toward the semi-annual purchase of the Company' common stock. The ESPP is qualified under Section 423 of the Internal Revenue Code. The employee's purchase price is derived from a formula based on the closing price of the common stock on the first day of the offering period versus the closing price on the date of purchase (or, if not a trading day, on the immediately preceding trading day). The offering period under the ESPP has a duration of six months, and the purchase price with respect to each offering period beginning on or after such date is, until otherwise amended, equal to 85% of the lesser of (i) the fair market value of the Company's common stock at the commencement of the applicable six-month offering period or (ii) the fair market value of the Company's common stock on the purchase date. The Company estimates the fair value of common stock under the ESPP using a Black-Scholes valuation model. The fair value was estimated on the date of grant using the Black-Scholes option valuation model and the straight-line attribution approach with the following weighted-average assumptions: risk-free interest rate (1.89%); expected term (0.5 years); expected volatility (65.5%); and an expected dividend yield (0%). The Company recorded an immaterial amount of stock-based compensation expense under the ESPP for the three and six months ended June 30, 2018 The total number of available ESPP shares is increased annually, beginning in 2016 and ending in 2025. The ESPP allows for share replenishment equal to the lesser of (i) 400,000 shares and (ii) 1% of the number of shares of the Company’s common stock outstanding on the last day of the preceding calendar year, or an amount determined by the Company’s Board of Directors. As of June 30, 2018, a total of 1.6 million shares were reserved and available for issuance under the ESPP.

Collaboration Revenue

Collaboration Revenue	6 Months Ended
	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Revenue	8 . Collaboration Revenue Adoption of ASC Topic 606, Revenue from Contracts with Customers The Company adopted ASC 606 on January 1, 2018, using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for 2018 reflect the application of ASC 606 guidance while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition (“ASC 605”), which is also referred to herein as "legacy GAAP" or the "previous guidance". The adoption of ASC 606 represents a change in accounting principle that will more closely align revenue recognition with the delivery of the Company's services and will provide financial statement readers with enhanced disclosures. Financial Statement Impact of Adopting ASC 606 The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018, was recorded as an adjustment to accumulated deficit as of the adoption date. As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made to accounts on the condensed consolidated balance sheet as of January 1, 2018: As Reported at Adjustments Due to Balance at December 31, 2017 ASC 606 January 1, 2018 Deferred revenue - related party 12,079 5,339 17,418 Deferred revenue, net of current portion - related party 84,847 21,518 106,365 Accumulated deficit (263,571 ) (26,857 ) (290,428 ) Collaboration Revenue The adoption of ASC 606 changed the pattern and timing of revenue recognition under the Company’s license and collaboration agreement with NHS. Under ASC 605, the upfront fee of $120,000 received by the Company in the first quarter of 2016 was deferred and recognized on a straight-line basis over the estimated performance period of 10 years. In addition, the Company recognized revenue associated with substantive development milestones not considered probable at the inception of the license and collaboration agreement with NHS in their entirety in the period in which the milestone was achieved, in accordance with FASB ASC Topic 605-28, Revenue Recognition-Milestone Method . Under ASC 606, the Company recognizes revenue using the cost-to-cost method which best depicts the transfer of control to the customer. Under the cost-to-cost method, the extent of progress towards completion is measured based on the ratio of actual costs incurred to the total estimated costs expected upon satisfying the identified performance obligation. Under this method, revenue will be recorded as a percentage of the estimated transaction price based on the extent of progress towards completion. The estimate of the Company’s measure of progress and estimate of transaction price will be updated at each reporting date, as a change in estimate, and will require judgement. The amount of consideration allocated to satisfied performance obligations, based on the Company’s measure of progress will be recognized immediately on a cumulative catch-up basis, resulting in an adjustment to revenue in the period of change. The amount related to the unsatisfied portion will be recognized as that portion is satisfied over time. In addition, substantive development milestones, which were previously recognized in the period when the milestone was achieved, will be recognized over the remaining performance period under ASC 606. As the adoption method does not result in a recast of the prior year consolidated financial statements, ASC 606 requires the Company to provide additional disclosures during the year of adoption of the amount by which each financial statement line item is affected by adoption of the new standard and explanations of the reasons for significant changes . We do not assess whether a contract has a significant financing component if the expectation at contract inception is that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. We expense incremental costs of obtaining a contract as and when incurred if the expected amortization period of the asset that we would have recognized is one year, or less or the amount is immaterial. At June 30, 2018, we have not capitalized any costs to obtain any of our contracts. Income Taxes The adoption of ASC 606 resulted in an increase to deferred revenue, which in turn generated an additional deferred tax asset that increased the Company’s net deferred tax asset position. As the Company fully reserves its net deferred tax assets, the impact was offset by the valuation allowance. Impact of New Revenue Guidance on Financial Statement Line Items The following table compares the reported condensed consolidated balance sheet, statement of operations and cash flows, as of and for the three and six months ended June 30, 2018 to the pro-forma amounts had the previous guidance (ASC 605) been in effect: As of June 30, 2018 As Reported under ASC 606 Pro forma as if accounted for under ASC 605 Deferred revenue - related party 17,962 12,097 Deferred revenue, net of current portion - related party 97,959 78,922 Accumulated deficit (346,136 ) (321,234 ) Total reported liabilities were $24,902 greater as reported under ASC 606 than would have been reported under ASC 605 as of June 30, 2018. This change consists of a $19,037 increase in deferred revenue, net of current portion, related party, and a $5,865 increase in deferred revenue - related parties. Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As Reported under ASC 606 Pro forma as if accounted for under ASC 605 As Reported under ASC 606 Pro forma as if accounted for under ASC 605 Collaboration revenue - related party $ 4,271 $ 3,024 $ 8,037 $ 6,083 Loss from operations (28,136 ) (29,383 ) (56,402 ) (58,356 ) Net loss $ (27,787 ) $ (29,034 ) $ (55,706 ) $ (57,660 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.68 ) $ (0.71 ) $ (1.37 ) $ (1.42 ) Collaboration revenue – related party increased by approximately $1,247 and $1,954 as reported under ASC 606 when compared to what would have been reported under ASC 605 for the three and six months ended June 30, 2018 Six Months Ended June 30, 2018 As Reported under ASC 606 Pro forma as if accounted for under ASC 605 Net loss $ (55,706 ) $ (57,660 ) Deferred revenue (7,863 ) (5,909 ) The adoption of ASC 606 resulted in a $1,954 decrease in net loss for the period, due to a corresponding increase in revenue. This was offset by an increase of $1,954 in the change in deferred revenue for the quarter. Revenue Recognition Revenue is recognized when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaboration Revenue The Company currently generates its revenue through a collaboration and license agreement for the development and commercialization of product candidates. The collaboration and license agreement is within the scope of ASC 606. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligation(s); and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for an arrangement that contains multiple performance obligations, the Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associate milestone value is allocated to that distinct good or service and revenue is recognized in the period in which the milestone is achieved. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the Company evaluates the milestone to determine whether the milestone is considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall allocation. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and earnings in the period of adjustment. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). Transaction Price Allocated to Future Performance Obligations Remaining performance obligations represents the transaction price of contracts for which work has not been performed (or has been partially performed) and excludes unexercised contract options. As of June 30, 2018, the aggregate amount of the transaction price allocated to the remaining performance obligation was approximately $151,000. Contract Balances from Contracts with Customers The following table presents changes in the Company’s contract assets, which are included in prepaid expenses and other current assets, and contract liabilities during the six months ended June 30, 2018 and 2017 (in thousands): Balance as of January 1, 2018 Additions Deductions Balance as of June 30, 2018 Six months ended June 30, 2018 Contract assets 510 175 (510 ) 175 Contract liabilities: Deferred revenue 123,783 175 (8,037 ) 115,921 Balance as of January 1, 2017 Additions Deductions Balance as of June 30, 2017 Six months ended June 30, 2017 Contract assets 306 — (8 ) 298 Contract liabilities: Deferred revenue 108,814 — (6,029 ) 102,785 During the three and six months ended June 30, 2018 we recognized the following revenues as a result of changes in the contract asset and the contract liability balances in the respective periods (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Revenue recognized in the period from: Amounts included in the contract liability at the beginning of the period 4,271 3,014 8,037 6,029 The timing of revenue recognition, billings and cash collections results in contract assets and contract liabilities on the consolidated balance sheets. When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded. Contract liabilities are recognized as revenue after control of the products or services is transferred to the customer and all revenue recognition criteria have been met. License and Collaboration Arrangements In January 2016, the Company entered into the Collaboration and License Agreement (“License Agreement”) with NHS for the development and commercialization of certain product candidates in development for the treatment and management of CDI and IBD, including UC and Crohn’s disease. The License Agreement supports the development of the Company’s portfolio of products for CDI and IBD in markets outside of the United States and Canada (the “Licensed Territory”). The Company has retained full commercial rights to its entire portfolio of product candidates with respect to the United States and Canada. Under the License Agreement, the Company granted to NHS an exclusive, royalty-bearing license to develop and commercialize, in the Licensed Territory, certain products based on its microbiome technology that are being developed for the treatment of CDI and IBD, including SER-109, SER-262, SER-287 and SER-301 (collectively, the “NHS Collaboration Products”). The License Agreement sets forth the Company’s and NHS’ respective obligations for development, commercialization, regulatory and manufacturing and supply activities for the NHS Collaboration Products with respect to the licensed fields and the Licensed Territory. In exchange for the license, NHS agreed to pay the Company an upfront cash payment of $120,000, which the Company received in February 2016. NHS also agreed to pay the Company tiered royalties, at percentages ranging from the high single digits to high teens, of net sales of NHS Collaboration Products in the Licensed Territory. The Company is eligible to receive up to $285,000 in development milestone payments, $375,000 in regulatory payments and up to an aggregate of $1,125,000 for the achievement of certain commercial milestones related to the sales of NHS Collaboration Products. The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty NHS, is a customer. The Company identified the following promises under the contract: (i) a license to develop and commercialize the NHS Collaboration Products in the Licensed Territory, (ii) obligation to perform research and development services, (iii) participation on a joint steering committee, and (iv) manufacturing services to provide clinical supply to complete future clinical trials. In addition, the Company identified a contingent obligation to perform manufacturing services to provide commercial supply if commercialization occurs, which is contingent upon regulatory approval. This contingent obligation has been excluded from allocation performed at the inception of the arrangement. The Company assessed the promised goods and services to determine if they are distinct. Based on this assessment, the Company determined that the promised goods and services do not have standalone value and are highly interrelated. Accordingly, the promised goods and services represent one performance obligation. At contract inception, the Company determined that the $120,000 non-refundable upfront amount constituted the entirety of the consideration to be included in the transaction price as the development, regulatory, and commercial milestones were fully constrained. During the year ended December 31, 2016, the Company received $10,000 from NHS in connection with the initiation of the Phase 1b study for SER-262 in CDI. During the year ended December 31, 2017, the Company received $20,000 from NHS in connection with the initiation of the Phase 3 study for SER-109. The transaction price as of January 1, 2018 was approximately $151,000. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as they were determined to relate predominantly to the license granted to NHS and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. During the three and six months ended June 30, 2018 and 2017 the Company recognized $4,271, $8,037, $3,014 and $6,029, respectively, of related party revenue (see Note 12 “Related Party Transactions”) associated with the License Agreement. As of June 30, 2018, there was $115,921 of deferred revenue related to the License Agreement, which is classified as current or non-current in the consolidated balance sheets based on the Company’s estimate of revenue that will be recognized within the next 12 months. All costs associated with the License Agreement are recorded in research and development expense in the condensed consolidated statements of operations and comprehensive loss.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	9 . Income Taxes The Company did not provide for any income taxes for the six-month period ended June 30, 2018 or 2017. The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of June 30, 2018 and December 31, 2017. Management reevaluates the positive and negative evidence at each reporting period. As of June 30, 2018 and December 31, 2017, the Company had no accrued interest or tax penalties recorded. The Company files income tax returns in the United States and various state jurisdictions. The Company is no longer subject to U.S. federal income tax examinations by tax authorities for years before 2012. However, to the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated my still be adjusted upon examination by the Internal Revenue Service or state tax authorities to the extent it is utilized in a future period. There are no currently ongoing or pending examinations in any jurisdictions. As disclosed in the Company’s 2017 Form 10-K, the Company recorded the tax effects of the 2017 Tax Cuts and Jobs Act (TCJA) based on provisional amounts permitted in accordance with Staff Accounting Bulletin No. 118. The Company is still analyzing certain aspects of the TCJA and refining its calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts, but the Company does not expect there to be a material change in the estimates.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	10 . Commitments and Contingencies Leases On November 11, 2015, the Company entered into a non-cancelable property lease with BMR-Sidney Research Campus LLC (“BMR”) for 83,396 square feet of office, laboratory and pilot manufacturing space at 200 Sidney Street, Cambridge, Massachusetts. The lease term commenced in March 2016 and ends in November 2023. The Company has the option to extend the lease twice, each for a five-year period. The Company moved its corporate headquarters to this location in April 2016. BMR has contributed a total of $12,509 toward the cost of tenant improvements. BMR’s contributions toward the cost of tenant improvements is recorded as a lease incentive obligation on the Company’s consolidated balance sheet. The lease incentive obligation is amortized to the Company’s consolidated statement of operations as reductions to rent expense over the lease term. As of June 30, 2018, the Company has recorded a lease incentive obligation of $9,428. During the six months ended June 30, 2018, the Company amortized $884 of this lease incentive obligation as a reduction to rent expense. During the three and six months ended June 30, 2018 and 2017, the Company recognized $1,107, $2,206, $1,145 and $2,244 respectively, of rental expense related to office and laboratory space. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of June 30, 2018 or December 31, 2017. Legal Contingencies The Company accrues a liability for legal contingencies when it believes that it is both probable that a liability has been incurred and that the Company can reasonably estimate the amount of the loss. The Company reviews these accruals and adjusts them to reflect ongoing negotiations, settlements, rulings, advice of legal counsel and other relevant information. To the extent new information is obtained and the views on the probable outcomes of claims, suits, assessments, investigations or legal proceedings change, changes in the Company’s accrued liabilities would be recorded in the period in which such determination is made. In addition, in accordance with the relevant authoritative guidance, for any matters in which the likelihood of material loss is at least reasonably possible, the Company will provide disclosure of the possible loss or range of loss. If a reasonable estimate cannot be made, however, the Company will provide disclosure to that effect. The Company expenses legal costs as they are incurred. On March 30, 2018, the U.S. District Court for the District of Massachusetts granted the Company’s motion to dismiss the a putative class action lawsuit filed September 28, 2016, entitled Mazurek v. Seres Therapeutics, Inc., et.al., The Company did not accrue any liabilities related to legal contingencies in its consolidated financial statements as of June 30, 2018 or December 31, 2017.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	11 . Related Party Transactions As described in Note 8, in January 2016 the Company entered into a License Agreement with NHS for the development and commercialization of certain product candidates in development for the treatment and management of CDI and IBD, including UC and Crohn’s disease. NHS is a related party since NHS is an affiliate of Nestlé Health Science, one of the Company’s significant stockholders. During the three and six months ended June 30, 2018 and 2017, the Company recognized $4,271, $8,037, $3,014 and $6,029 of related party revenue associated with the License Agreement. As of June 30, 2018, there was $115,921 of deferred revenue related to the License Agreement, which is classified as current or non-current in the consolidated balance sheets. The Company has made no payments to NHS during the three and six months ended June 30, 2018. There is $175 due from NHS as of June 30, 2018 for the reimbursement of development costs, which is classified as other current assets in the Company’s consolidated balance sheet.

Summary of Significant Accoun18

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
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 reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Net Loss per Share	Net Loss per Share Basic net loss per share is computed using the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed using the sum of the weighted average number of common shares outstanding during the period and, if dilutive, the weighted average number of potential shares of common stock, including the assumed exercise of stock options and warrants and unvested restricted stock. The restricted stock units granted by the Company entitle the holder of such awards to dividends declared or paid by the board of directors, regardless of whether such awards are unvested, as if such shares were outstanding common shares at the time of the dividend. However, the unvested restricted stock units are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three and Six Months Ended June 30, 2018 2017 Stock options to purchase common stock 7,481,478 6,314,838 Unvested restricted stock units 289,248 408,400 7,770,726 6,723,238
Recently Issued Accounting Standards	Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board (the “FASB”) issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers The Company has adopted this standard as of the required effective date of January 1, 2018, In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Leases (Topic 842) In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU 2016-18, Restricted Cash The Company’s statements of cash flows includes restricted cash with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on such statements. A reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows is as follows: June 30, December June 30, December 2018 2017 2017 2016 Cash and cash equivalents $ 57,960 $ 36,088 $ 33,642 $ 54,539 Restricted cash 1,513 1,513 1,513 1,400 Total cash, cash equivalents and restricted cash as shown in the statement of cash flows $ 59,473 $ 37,601 $ 35,155 $ 55,939 In June 2018, the FASB issued ASU 2018-07, “Compensation – Stock Compensation (Topic 718).” ASU 2018-07 simplifies the accounting for nonemployee share-based payment transactions. This ASU is effective for public entities for interim and annual reporting periods beginning after December 15, 2018. The Company is currently in the process of evaluating the impact of the guidance on its consolidated financial statements.

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share	The following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three and Six Months Ended June 30, 2018 2017 Stock options to purchase common stock 7,481,478 6,314,838 Unvested restricted stock units 289,248 408,400 7,770,726 6,723,238
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	A reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows is as follows: June 30, December June 30, December 2018 2017 2017 2016 Cash and cash equivalents $ 57,960 $ 36,088 $ 33,642 $ 54,539 Restricted cash 1,513 1,513 1,513 1,400 Total cash, cash equivalents and restricted cash as shown in the statement of cash flows $ 59,473 $ 37,601 $ 35,155 $ 55,939

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table presents information about the Company’s assets as of June 30, 2018 and December 31, 2017 that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (note there were no liabilities measured at fair value on a recurring basis in either of the periods presented): Fair Value Measurements as of June 30, 2018 Using: Level 1 Level 2 Level 3 Not Subject to Leveling (1) Total Assets: Cash Equivalents $ — $ 2,992 $ — $ 44,306 $ 47,298 Investments: Commercial Paper $ — $ 10,717 $ — $ — $ 10,717 Certificates of Deposit — 3,430 — — 3,430 Corporate Bonds — 6,744 — — 6,744 Government Securities — 3,746 — — 3,746 Treasury Bonds — 13,469 — — 13,469 $ — $ 41,098 $ — $ 44,306 $ 85,404 (1) Fair Value Measurements as of December 31, 2017 Using: Level 1 Level 2 Level 3 Not Subject to Leveling (1) Total Assets: Cash Equivalents $ — $ — $ — $ 25,964 $ 25,964 Investments: Commercial Paper $ — $ 6,198 $ — $ — $ 6,198 Certificates of Deposit — 8,916 8,916 Corporate Bonds — 58,865 — — 58,865 Government Securities — 22,954 — — 22,954 Treasury Bonds — 16,962 — — 16,962 $ — $ 113,895 $ — $ 25,964 $ 139,859 (1)

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2018
Investments Debt And Equity Securities [Abstract]
Schedule of Fair Value of Available-for-Sale Investments by Type of Security	As of June 30, 2018 and December 31, 2017, the fair value of available-for-sale investments by type of security was as follows: June 30, 2018 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Commercial Paper $ 10,717 $ — $ — $ 10,717 Certificates of Deposit 3,430 — — 3,430 Corporate Bonds 6,754 — (10 ) 6,744 Government Securities 3,747 — (1 ) 3,746 Treasury Bonds 13,486 — (17 ) 13,469 $ 38,134 $ — (28 ) $ 38,106 December 31, 2017 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Commercial Paper $ 6,198 $ — $ — $ 6,198 Certificates of Deposit 8,916 — — 8,916 Corporate Bonds 58,937 — (72 ) 58,865 Government Securities 22,997 — (43 ) 22,954 Treasury Bonds 16,992 — (30 ) 16,962 $ 114,040 $ — $ (145 ) $ 113,895

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	6 Months Ended
	Jun. 30, 2018
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following: June 30, 2018 December 31, 2017 Laboratory equipment $ 13,988 13,181 Computer equipment 2,852 2,832 Furniture and office equipment 1,033 1,033 Leasehold improvements 27,977 27,963 Construction in progress 388 361 46,238 45,370 Less: Accumulated depreciation and amortization $ (16,334 ) $ (12,439 ) $ 29,904 $ 32,931

Accrued Expenses and Other Cu23

Accrued Expenses and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2018
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: June 30, 2018 December 31, 2017 Development and manufacturing costs $ 7,163 $ 3,910 Payroll and payroll-related costs 3,132 4,962 Professional fees 455 344 Facility and other 2,901 3,297 $ 13,651 $ 12,513

Stockholders' Equity Common S24

Stockholders' Equity Common Stock (Tables)	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity since December 31, 2017: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding as of December 31, 2017 6,125,692 $ 13.00 7.70 $ 15,808 Granted 1,732,276 10.16 Exercised (140,066 ) 0.68 Forfeited (236,424 ) 16.95 Outstanding as of June 30, 2018 7,481,478 $ 12.45 7.75 $ 11,509 Options vested and expected to vest as of June 30, 2018 7,481,478 12.45 7.75 11,509 Options exercisable as of June 30, 2018 3,987,920 $ 11.87 6.78 $ 11,390
Summary of Restricted Stock Unit Activity	The Company has granted restricted stock units with time-based vesting conditions. The table below summarizes the Company’s restricted stock unit activity since December 31, 2017: Number of Shares Weighted Average Grant Date Fair Value Unvested restricted stock units as of December 31, 2017 356,778 $ 10.01 Granted — $ — Forfeited (6,030 ) $ 9.78 Vested (61,500 ) $ 10.12 Unvested restricted stock units as of June 30, 2018 289,248 $ 10.00
Summary of Stock Based Compensation Expense	The Company recorded stock-based compensation expense related to stock options, restricted stock units and ESPP plan in the following expense categories of its condensed consolidated statements of operations and comprehensive loss: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Research and development expenses $ 2,262 $ 2,094 $ 4,190 $ 3,967 General and administrative expenses 2,072 2,409 4,380 4,814 $ 4,334 $ 4,503 $ 8,570 $ 8,781

Collaboration Revenue (Tables)

Collaboration Revenue (Tables) - ASU 2014-09 [Member]	6 Months Ended
	Jun. 30, 2018
Adjustments to Accounts on Condensed Consolidated Balance Sheet	The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018, was recorded as an adjustment to accumulated deficit as of the adoption date. As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made to accounts on the condensed consolidated balance sheet as of January 1, 2018: As Reported at Adjustments Due to Balance at December 31, 2017 ASC 606 January 1, 2018 Deferred revenue - related party 12,079 5,339 17,418 Deferred revenue, net of current portion - related party 84,847 21,518 106,365 Accumulated deficit (263,571 ) (26,857 ) (290,428 )
Comparison of Reported Condensed Consolidated Balance Sheet, Statement of Operations and Cash Flows to Pro-forma Amounts	The following table compares the reported condensed consolidated balance sheet, statement of operations and cash flows, as of and for the three and six months ended June 30, 2018 to the pro-forma amounts had the previous guidance (ASC 605) been in effect: As of June 30, 2018 As Reported under ASC 606 Pro forma as if accounted for under ASC 605 Deferred revenue - related party 17,962 12,097 Deferred revenue, net of current portion - related party 97,959 78,922 Accumulated deficit (346,136 ) (321,234 ) Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As Reported under ASC 606 Pro forma as if accounted for under ASC 605 As Reported under ASC 606 Pro forma as if accounted for under ASC 605 Collaboration revenue - related party $ 4,271 $ 3,024 $ 8,037 $ 6,083 Loss from operations (28,136 ) (29,383 ) (56,402 ) (58,356 ) Net loss $ (27,787 ) $ (29,034 ) $ (55,706 ) $ (57,660 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.68 ) $ (0.71 ) $ (1.37 ) $ (1.42 ) Six Months Ended June 30, 2018 As Reported under ASC 606 Pro forma as if accounted for under ASC 605 Net loss $ (55,706 ) $ (57,660 ) Deferred revenue (7,863 ) (5,909 )
Changes in Contract Asset Included in Prepaid Expenses and Other Current Assets, and Contract Liabilities	The following table presents changes in the Company’s contract assets, which are included in prepaid expenses and other current assets, and contract liabilities during the six months ended June 30, 2018 and 2017 (in thousands): Balance as of January 1, 2018 Additions Deductions Balance as of June 30, 2018 Six months ended June 30, 2018 Contract assets 510 175 (510 ) 175 Contract liabilities: Deferred revenue 123,783 175 (8,037 ) 115,921 Balance as of January 1, 2017 Additions Deductions Balance as of June 30, 2017 Six months ended June 30, 2017 Contract assets 306 — (8 ) 298 Contract liabilities: Deferred revenue 108,814 — (6,029 ) 102,785 During the three and six months ended June 30, 2018 we recognized the following revenues as a result of changes in the contract asset and the contract liability balances in the respective periods (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Revenue recognized in the period from: Amounts included in the contract liability at the beginning of the period 4,271 3,014 8,037 6,029

Nature of the Business and Ba26

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Entity incorporated year	Oct. 31, 2010
Entity incorporated state name	State of Delaware
Accumulated deficit	$ 346,136	$ 263,571
Cash, cash equivalents and short-term investments	$ 96,100

Summary of Significant Accoun27

Summary of Significant Accounting Policies - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	7,770,726	6,723,238	7,770,726	6,723,238
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	7,481,478	6,314,838	7,481,478	6,314,838
Unvested Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	289,248	408,400	289,248	408,400

Summary of Significant Accoun28

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 57,960	$ 36,088	$ 33,642	$ 54,539
Restricted cash	1,513	1,513	1,513	1,400
Total cash, cash equivalents and restricted cash as shown in the statement of cash flows	$ 59,473	$ 37,601	$ 35,155	$ 55,939

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair value of liabilities on recurring basis	$ 0	$ 0
Fair value, assets transfers from Level 1 to Level 2 measurement	0
Fair value, assets transfers from Level 2 to Level 1 measurement	0
Fair Value, assets transfers into (out of) Level 3 measurement	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Assets:
Cash Equivalents		$ 47,298	$ 25,964
Investments:
Total assets		85,404	139,859
Fair Value, Inputs, Level 2 [Member]
Assets:
Cash Equivalents		2,992
Investments:
Total assets		41,098	113,895
Not Subject to Leveling [Member]
Assets:
Cash Equivalents	[1]	44,306	25,964
Investments:
Total assets	[1]	44,306	25,964
Commercial Paper [Member]
Investments:
Investments		10,717	6,198
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		10,717	6,198
Certificates of Deposit [Member]
Investments:
Investments		3,430	8,916
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		3,430	8,916
Corporate Bonds [Member]
Investments:
Investments		6,744	58,865
Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		6,744	58,865
Government Securities [Member]
Investments:
Investments		3,746	22,954
Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		3,746	22,954
Treasury Bonds [Member]
Investments:
Investments		13,469	16,962
Treasury Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Investments:
Investments		$ 13,469	$ 16,962
[1]	Certain cash equivalents and investments that are valued using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy.

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Available-for-Sale Investments by Type of Security (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 38,134	$ 114,040
Gross Unrealized Loss	(28)	(145)
Fair Value	38,106	113,895
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,717	6,198
Fair Value	10,717	6,198
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,430	8,916
Fair Value	3,430	8,916
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,754	58,937
Gross Unrealized Loss	(10)	(72)
Fair Value	6,744	58,865
Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,747	22,997
Gross Unrealized Loss	(1)	(43)
Fair Value	3,746	22,954
Treasury Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,486	16,992
Gross Unrealized Loss	(17)	(30)
Fair Value	$ 13,469	$ 16,962

Investments - Additional Inform

Investments - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018
Investments [Abstract]
Maximum maturity days for cash equivalents	90 days

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 46,238	$ 45,370
Less: Accumulated depreciation and amortization	(16,334)	(12,439)
Property and equipment, net	29,904	32,931
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	13,988	13,181
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,852	2,832
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,033	1,033
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,977	27,963
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 388	$ 361

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 1,954	$ 1,760	$ 3,895	$ 3,490

Accrued Expenses and Other Cu35

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Development and manufacturing costs	$ 7,163	$ 3,910
Payroll and payroll-related costs	3,132	4,962
Professional fees	455	344
Facility and other	2,901	3,297
Total Accrued Expenses and Other Current Liabilities	$ 13,651	$ 12,513

Stockholders' Equity Common S36

Stockholders' Equity Common Stock - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Equity [Abstract]
Number of Shares, Beginning Balance	6,125,692
Number of Shares, Granted	1,732,276
Number of Shares, Exercised	(140,066)
Number of Shares, Forfeited	(236,424)
Number of Shares, Ending Balance	7,481,478	6,125,692
Number of Shares, Options vested and expected to vest	7,481,478
Number of Shares, Options exercisable	3,987,920
Weighted Average Exercise Price, Beginning Balance	$ 13
Weighted Average Exercise Price, Granted	10.16
Weighted Average Exercise Price, Exercised	0.68
Weighted Average Exercise Price, Forfeited	16.95
Weighted Average Exercise Price, Ending Balance	12.45	$ 13
Weighted Average Exercise Price, Options vested and expected to vest	12.45
Weighted Average Exercise Price, Options exercisable	$ 11.87
Weighted Average Remaining Contractual Term, Outstanding	7 years 9 months	7 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	7 years 9 months
Weighted Average Remaining Contractual Term, Options exercisable	6 years 9 months 10 days
Aggregate Intrinsic Value, Outstanding	$ 11,509	$ 15,808
Aggregate Intrinsic Value, Options vested and expected to vest	11,509
Aggregate Intrinsic Value, Options exercisable	$ 11,390

Stockholders' Equity Common S37

Stockholders' Equity Common Stock - Stock Options - Additional Information (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Weighted average grant-date fair value of stock options	$ 6.89	$ 7.44	$ 5.82	$ 6.98

Stockholders' Equity Common S38

Stockholders' Equity Common Stock - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member]	6 Months Ended
	Jun. 30, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested restricted stock units, Beginning balance | shares	356,778
Number of Shares, Forfeited | shares	(6,030)
Number of Shares, Vested | shares	(61,500)
Number of Shares, Unvested restricted stock units, Ending balance | shares	289,248
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Beginning balance | $ / shares	$ 10.01
Weighted Average Grant Date Fair Value, Forfeited | $ / shares	9.78
Weighted Average Grant Date Fair Value, Vested | $ / shares	10.12
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Ending balance | $ / shares	$ 10

Stockholders' Equity Common S39

Stockholders' Equity Common Stock - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 4,334	$ 4,503	$ 8,570	$ 8,781
Research and development expenses [Member] | Stock Options, Restricted Stock Units and ESPP Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	2,262	2,094	4,190	3,967
General and administrative expenses [Member] | Stock Options, Restricted Stock Units and ESPP Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,072	$ 2,409	$ 4,380	$ 4,814

Stockholders' Equity Common S40

Stockholders' Equity Common Stock - Employee Stock Purchase Plan - Additional Information (Detail) - Employee Stock Purchase Plan [Member]	6 Months Ended
	Jun. 30, 2018shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of eligible earning contributed toward semi-annual purchase of common stock	15.00%
Offering period under the plan	6 months
Percentage of purchase price with respect to each offering period	85.00%
Risk-free interest rate	1.89%
Expected term (in years)	6 months
Expected volatility	65.50%
Expected dividend yield	0.00%
Aggregate shares of common stock reserved for issuance	1,600,000
Shares issued under ESPP	400,000
Percentage of common stock shares outstanding	1.00%

Collaboration Revenue - Adjustm

Collaboration Revenue - Adjustments to Accounts on Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party	$ 17,962		$ 12,079
Deferred revenue, net of current portion - related party	97,959		84,847
Accumulated deficit	$ (346,136)		$ (263,571)
ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party		$ 17,418
Deferred revenue, net of current portion - related party		106,365
Accumulated deficit		(290,428)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party		5,339
Deferred revenue, net of current portion - related party		21,518
Accumulated deficit		$ (26,857)

Collaboration Revenue - Additio

Collaboration Revenue - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Jan. 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Feb. 29, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration/license fee				$ 120,000	$ 120,000
Period of performance identifiable deliverables					10 years
Total reported liabilities		$ 146,209			$ 146,209		$ 128,823
Deferred revenue, net of current portion - related party		97,959			97,959		84,847
Deferred revenue - related party		17,962			17,962		12,079
Collaboration revenue - related party		4,271			8,037
Net Loss		(27,787)	$ (28,018)		(55,706)	$ (53,492)
Transaction price allocated to remaining performance obligations		151,000			151,000
Nestlé Health Science [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party		4,271	3,014		8,037	6,029
Transaction price allocated to remaining performance obligations									$ 151,000
Upfront cash payment		115,921			115,921					$ 120,000
Development milestone payments	$ 285,000
Regulatory payments	375,000
Sales based milestones	$ 1,125,000
Proceeds on achievement of development milestone							20,000	$ 10,000
Deferred revenue		115,921			115,921
ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, net of current portion - related party									106,365
Deferred revenue - related party									17,418
Upfront cash payment		115,921	$ 102,785		115,921	$ 102,785	$ 123,783	$ 108,814
Previous Accounting in Effect [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total reported liabilities		24,902			24,902
Deferred revenue, net of current portion - related party		(19,037)			(19,037)
Deferred revenue - related party		(5,865)			(5,865)
Difference Between Proforma Value and Reported Value [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party		1,247			$ 1,954
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, net of current portion - related party									21,518
Deferred revenue - related party									$ 5,339
Net Loss		$ (1,954)

Collaboration Revenue - Compari

Collaboration Revenue - Comparison of Reported Condensed Consolidated Balance Sheet to Pro-forma Amounts (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party	$ 17,962		$ 12,079
Deferred revenue, net of current portion - related party	97,959		84,847
Accumulated deficit	(346,136)		$ (263,571)
ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party		$ 17,418
Deferred revenue, net of current portion - related party		106,365
Accumulated deficit		$ (290,428)
Previous Accounting in Effect [Member] | ASU 2014-09 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party	(5,865)
Deferred revenue, net of current portion - related party	(19,037)
Previous Accounting in Effect [Member] | ASU 2014-09 [Member] | Pro Forma [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue - related party	12,097
Deferred revenue, net of current portion - related party	78,922
Accumulated deficit	$ (321,234)

Collaboration Revenue - Compa44

Collaboration Revenue - Comparison of Reported Condensed Consolidated Statement of Operations to Pro-forma Amounts (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party	$ 4,271		$ 8,037
Loss from operations	(28,136)	$ (28,416)	(56,402)	$ (54,306)
Net loss	$ (27,787)	$ (28,018)	$ (55,706)	$ (53,492)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.68)	$ (0.69)	$ (1.37)	$ (1.32)
Previous Accounting in Effect [Member] | ASU 2014-09 [Member] | Pro Forma [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party	$ 3,024		$ 6,083
Loss from operations	(29,383)		(58,356)
Net loss	$ (29,034)		$ (57,660)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.71)		$ (1.42)

Collaboration Revenue - Compa45

Collaboration Revenue - Comparison of Reported Condensed Consolidated Cash Flows to Pro-forma Amounts (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Net loss	$ (27,787)	$ (28,018)	$ (55,706)	$ (53,492)
Deferred revenue			(7,863)	$ (6,029)
Previous Accounting in Effect [Member] | ASU 2014-09 [Member] | Pro Forma [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Net loss	$ (29,034)		(57,660)
Deferred revenue			$ (5,909)

Collaboration Revenue - Changes

Collaboration Revenue - Changes in Contract Asset Included in Prepaid Expenses and Other Current Assets, and Contract Liabilities (Detail) - ASU 2014-09 [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract assets, Balance at Beginning of Period			$ 510	$ 306
Contract assets, Additions			175
Contract assets, Deductions			(510)	(8)
Contract assets, Balance at End of Period	$ 175	$ 298	175	298
Contract liabilities:
Balance at Beginning of Period			123,783	108,814
Additions			175
Deductions	(4,271)	(3,014)	(8,037)	(6,029)
Balance at End of Period	$ 115,921	$ 102,785	$ 115,921	$ 102,785

Collaboration Revenue - Schedul

Collaboration Revenue - Schedule of Revenue Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
ASU 2014-09 [Member]
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$ 4,271	$ 3,014	$ 8,037	$ 6,029

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0
Accrued interest or tax penalties	$ 0		$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Nov. 11, 2015USD ($)ft²	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Indemnification Agreement [Member]
Other Commitments [Line Items]
Indemnification obligations accrued		$ 0		$ 0		$ 0
Office and Laboratory Space [Member]
Other Commitments [Line Items]
Rental expense related to office and laboratory space		1,107,000	$ 1,145,000	$ 2,206,000	$ 2,244,000
BMR Sidney Research Campus LLC [Member]
Other Commitments [Line Items]
Non-cancelable property lease, description				On November 11, 2015, the Company entered into a non-cancelable property lease with BMR-Sidney Research Campus LLC (“BMR”) for 83,396 square feet of office, laboratory and pilot manufacturing space at 200 Sidney Street, Cambridge, Massachusetts. The lease term commenced in March 2016 and ends in November 2023. The Company has the option to extend the lease twice, each for a five-year period. The Company moved its corporate headquarters to this location in April 2016
Square feet of property subject to non-cancelable lease | ft²	83,396
Lease commencement period				2016-03
Lease expiration period				2023-11
Cost of tenant improvements	$ 12,509,000
Lease incentive obligation		$ 9,428,000		$ 9,428,000
Amortized of lease incentive obligation				$ 884,000

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - Nestlé Health Science [Member] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Feb. 29, 2016
Related Party Transaction [Line Items]
Collaboration revenue - related party	$ 4,271,000	$ 3,014,000	$ 8,037,000	$ 6,029,000
Deferred revenue	115,921,000		115,921,000		$ 120,000,000
Payments under agreements with related party	0		0
Due from related party for the reimbursement of development costs	$ 175,000		$ 175,000