View Filing Data

Research and development expenses

^[1]

$ 21,766

Total revenue

21,766

Operating expenses:

81,989

$ 38,095

$ 10,718

General and administrative expenses

32,616

16,761

4,364

Total operating expenses

114,605

54,856

15,082

Loss from operations

(92,839)

(54,856)

(15,082)

Other income (expense):

Interest income

2,229

638

Interest expense

(969)

(555)

(209)

Revaluation of preferred stock warrant liability

(7)

(1,418)

Total other income (expense), net

1,260

(1,627)

Net loss

(91,579)

(54,780)

(16,709)

Accretion of convertible preferred stock to redemption value

(1,291)

Net loss attributable to common stockholders

$ (91,579)

$ (54,780)

$ (18,000)

Net loss per share attributable to common stockholders, basic and diluted

$ (2.30)

$ (2.33)

$ (2.67)

Weighted average common shares outstanding, basic and diluted

39,846,928

23,532,400

6,748,037

Other comprehensive income (loss):

Unrealized gain (loss) on investments, net of tax of $0

$ (179)

$ 30

Total other comprehensive income (loss)

(179)

Comprehensive loss

$ (91,758)

$ (54,750)

$ (18,000)

[1]

In January 2016, the Company entered into a Collaboration and License Agreement with NHS for the development and commercialization of certain of its product candidates. In exchange for the license, NHS paid the Company an upfront cash payment of $120 million, which the Company received in February 2016 and is being recognized as revenue over the ten year performance period. During the quarter ended September 30, 2016, the Company received $10 million from NHS related to achievement of a milestone within this agreement, which was recognized in full as related party collaboration revenue during 2016.

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Unrealized gain (loss) on investment, tax	$ 0	$ 0	$ 0

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]	Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member]	Series B Convertible Preferred Stock [Member]	Series C Convertible Preferred Stock [Member]	Series D and D-1 Convertible Preferred Stock [Member]	Series D Convertible Preferred Stock [Member]
Stockholders' (deficit), value, beginning balance at Dec. 31, 2013	$ (11,116)	$ 7			$ (11,123)
Stockholders' (deficit), shares, beginning balance at Dec. 31, 2013		6,855,000
Convertible preferred stock, value, beginning balance at Dec. 31, 2013						$ 11,583
Convertible preferred stock, shares, beginning balance at Dec. 31, 2013						10,478,189
Issuance of convertible preferred stock, net of issuance costs, value							$ 10,558	$ 47,813	$ 64,832
Issuance of convertible preferred stock, net of issuance costs, shares							4,831,359	3,946,328	3,611,111
Issuance of common stock upon exercise of stock options, value	5		$ 5
Issuance of common stock upon exercise of stock options, shares		28,687
Issuance of common stock upon completion of initial public offering, net of offering costs, value	5		5
Issuance of common stock upon completion of initial public offering, net of offering costs, shares		6,563
Issuance of common stock upon exercise of common stock warrant, value	317		317
Stock-based compensation expense	2,068		2,068
Accretion of convertible preferred stock to redemption value						$ 1,291
Accretion of convertible preferred stock to redemption value, impact on permanent equity	(1,291)		(1,291)
Issuance costs of convertible preferred stock							$ (71)	$ (187)	$ (168)
Net loss	(16,709)				(16,709)
Stockholders' (deficit), value, ending balance at Dec. 31, 2014	(26,721)	$ 7	1,104		(27,832)
Stockholders' (deficit), shares, ending balance at Dec. 31, 2014		6,890,250
Convertible preferred stock, value, ending balance at Dec. 31, 2014						$ 136,077
Convertible preferred stock, shares, ending balance at Dec. 31, 2014						22,866,987
Issuance of common stock upon exercise of stock options, value	93		93
Issuance of common stock upon exercise of stock options, shares		232,970
Issuance of common stock upon completion of initial public offering, net of offering costs, value	139,267	$ 8	139,259
Issuance of common stock upon completion of initial public offering, net of offering costs, shares		8,545,138
Issuance of common stock upon exercise of common stock warrant, value	169	$ 1	168
Issuance of common stock upon exercise of common stock warrant, shares		546,672
Stock-based compensation expense	9,694		9,694
Issuance costs of convertible preferred stock										$ (24)
Reclassification of preferred stock warrant liability	1,589		1,589
Conversion of convertible preferred stock upon listing, value	136,053	$ 23	136,030			$ (136,053)
Conversion of convertible preferred stock upon listing, shares		22,866,987				(22,866,987)
Unrealized gain (loss) on investments	30			$ 30
Net loss	(54,780)				(54,780)
Stockholders' (deficit), value, ending balance at Dec. 31, 2015	$ 205,394	$ 39	287,937	30	(82,612)
Stockholders' (deficit), shares, ending balance at Dec. 31, 2015	39,082,017	39,082,017
Issuance of common stock upon exercise of stock options, value	$ 2,138	$ 1	2,137
Issuance of common stock upon exercise of stock options, shares	1,273,736	1,273,736
Stock-based compensation expense	$ 16,857		16,857
Unrealized gain (loss) on investments	(179)			(179)
Net loss	(91,579)				(91,579)
Stockholders' (deficit), value, ending balance at Dec. 31, 2016	$ 132,631	$ 40	$ 306,931	$ (149)	$ (174,191)
Stockholders' (deficit), shares, ending balance at Dec. 31, 2016	40,355,753	40,355,753

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2014 USD ($)
Series B Convertible Preferred Stock [Member]
Issuance costs of convertible preferred stock	$ 71
Series C Convertible Preferred Stock [Member]
Issuance costs of convertible preferred stock	187
Series D and D-1 Convertible Preferred Stock [Member]
Issuance costs of convertible preferred stock	$ 168

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (91,579)	$ (54,780)	$ (16,709)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense	16,857	9,694	2,068
Depreciation and amortization expense	4,205	728	190
Loss from revaluation of preferred stock warrant liability		7	1,418
Licensing fees paid in common stock warrant			317
Non-cash interest expense		367	81
Accretion of discount on investments	(386)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,598)	(2,470)	(7)
Deferred revenue	108,814
Accounts payable	3,581	2,682	810
Accrued expenses and other liabilities	5,027	2,928	1,474
Net cash provided by (used in) operating activities	43,921	(40,844)	(10,358)
Cash flows from investing activities:
Purchases of property and equipment	(21,492)	(4,362)	(1,001)
Purchases of investments	(290,594)	(267,761)
Sales and maturities of investments	246,494	136,390
Changes in restricted cash	139	(1,400)	(102)
Net cash used in investing activities	(65,453)	(137,133)	(1,103)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs		(24)	123,203
Proceeds from issuance of notes payable and preferred stock warrant, net of issuance costs			2,000
Proceeds from exercise of stock options and common stock warrants	2,138	262	5
Proceeds from issuance of common stock upon completion of initial public offering		143,015
Proceeds from issuance of common stock and restricted common stock			5
Repayment of notes payable		(2,600)	(400)
Payments of initial public offering costs		(2,928)	(821)
Net cash provided by financing activities	2,138	137,725	123,992
Net increase (decrease) in cash and cash equivalents	(19,394)	(40,252)	112,531
Cash and cash equivalents at beginning of year	73,933	114,185	1,654
Cash and cash equivalents at end of year	54,539	73,933	114,185
Supplemental disclosure of cash flow information:
Cash paid for interest	109	163	122
Supplemental disclosure of non-cash investing and financing activities:
Accretion of convertible preferred stock to redemption value			1,291
Deferred offering costs included in accounts payable			863
Property and equipment purchases included in accounts payable and accrued expenses	$ 1,650	$ 2,953	$ 101

Nature of the Business and Basis of Presentation

12 Months Ended

Dec. 31, 2016

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 prevent further 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. Using its microbiome therapeutics platform, the Company is developing additional product candidates to treat diseases where the microbiome is implicated, including SER-262, a synthetic product candidate, to prevent an initial recurrence of primary CDI, SER-287 to treat ulcerative colitis, SER-301, a synthetic inflammatory bowel disease product candidate, and SER-155, a synthetic product candidate, to improve clinical outcomes following allogeneic hematopoietic stem cell transplantation (allo-HSCT) due to infections and graft-versus-host disease. The Company is also using its microbiome therapeutics platform to conduct research on metabolic diseases, such as non-alcoholic steatohepatitis (NASH); inflammatory diseases, such as Crohn’s disease; rare liver disorders such as primary sclerosing cholangitis (PSC); and immuno-oncology treatments.

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.

The Company’s consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. The Company has experienced negative cash flows and had an accumulated deficit of $174,191 and $82,612 as of December 31, 2016 and 2015, respectively. The Company expects that its cash, cash equivalents and investments at December 31, 2016 of $229,995 will enable it to fund its operating expense and capital expenditure requirements through 2018. The future viability of the Company is dependent on its ability to generate cash from operating activities or to raise additional capital to finance its operations. The Company’s failure to raise capital as and when needed could have a negative impact on its financial condition and ability to pursue its business strategies.

On July 1, 2015, the Company completed an initial public offering (“IPO”) of its common stock, and issued and sold 8,545,138 shares of common stock at a price to the public of $18.00 per share, resulting in net proceeds of approximately $139,267 after deducting underwriting discounts and commissions and offering expenses. The shares issued upon closing of the IPO included 1,114,583 shares of the Company’s common stock, which were sold to the underwriters pursuant to the full exercise of their option to purchase additional shares of common stock. Upon the listing of the Company’s common stock on The NASDAQ Global Select Market (“NASDAQ”) on June 26, 2015, all outstanding shares of the Company’s convertible preferred stock automatically converted into 22,866,987 shares of the Company’s common stock. In addition, at this time, the warrant to purchase shares of the Company’s Series A-2 convertible preferred stock was converted into a warrant to purchase shares of the Company’s common stock.

The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries after elimination of all intercompany accounts and transactions.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

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, the accrual of research and development expenses and the valuation of common stock, stock-based awards and the preferred stock warrant liability. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Cash Equivalents

The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market accounts, corporate bonds, and certificates of deposit purchased with original maturities of less than 90 days from the date of purchase, are stated at fair value.

Restricted Cash

The Company held cash of $1,400 as of December 31, 2016 and $1,539 as of December 31, 2015 in a separate restricted bank account as a security deposit for the lease of the Company’s facilities. The Company has classified these deposits as long-term restricted cash on its balance sheet.

Investments

The Company classifies its available-for-sale investments as current assets on the consolidated balance sheet if they mature within one year from the balance sheet date.

The Company classifies all of its investments as available-for-sale securities. The Company’s investments are measured and reported at fair value using quoted prices in active markets for similar securities. Unrealized gains and losses on available-for-sale securities are reported as a separate component of stockholders’ equity (deficit). The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the consolidated statement of operations and comprehensive loss. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary”, the Company reduces the investment to fair value through a charge to the consolidated statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company has all cash, cash equivalents and investments balances at one accredited financial institution, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third-party manufacturers to supply products for research and development activities of its programs, including pre-clinical and clinical testing. These programs could be adversely affected by a significant interruption in the supply of such drug substance products.

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 (see Note 3). 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 carrying values of the Company’s accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities.

Deferred Offering Costs

The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs (non-current) until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the financing. As of December 31, 2016 and 2015 the Company had recorded no deferred offering costs. On July 1, 2015, the Company reclassified $3,748 of deferred offering costs to additional paid in capital as a reduction of the proceeds from the IPO.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the useful life of the asset. Laboratory equipment is depreciated over five years. Computer equipment and furniture and office equipment are depreciated over three years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expenses include salaries, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both pre-clinical studies and clinical trials.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.

Accounting for Stock-Based Compensation

The Company measures all stock options and other stock-based awards granted to employees and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock options, restricted stock units and restricted stock awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. For stock options or restricted stock units issued with performance-based vesting conditions, the stock compensation expense related to these awards is recognized based on the grant date fair value when achievement of the performance condition is deemed probable.

The Company measures stock-based awards granted to consultants and non-employees based on the fair value of the award on the date on which the related service is complete. Compensation expense is recognized over the period during which services are rendered by such consultants and non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is remeasured using the then-current fair value of the Company’s common stock and updated assumption inputs in the Black-Scholes option-pricing model.

The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified.

The Company recognizes adjustments to stock compensation expense for forfeitures as they occur.

The fair value of each stock option grant is estimated on the date of grant using the Black- Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

Revenue Recognition

The Company currently generates its revenue through collaboration and license arrangements with strategic partners for the development and commercialization of product candidates.

The Company recognizes revenue in accordance with FASB ASC Topic 605, Revenue Recognition (“ASC 605”). Accordingly, revenue is recognized for each unit of accounting when all of the following criteria are met:

•

Persuasive evidence of an arrangement exists

•

Delivery has occurred or services have been rendered

•

The seller’s price to the buyer is fixed or determinable

•

Collectability is reasonably assured

Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s consolidated balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, current portion. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as long-term deferred revenue.

Collaboration Revenue

In January 2016 the Company entered into a Collaboration and License Agreement (the “License Agreement”) with Nestec Ltd. (“NHS”), an affiliate of Nestlé Health Science US Holdings, Inc. In connection with the License Agreement, the Company received an upfront, non-refundable payment of $120,000. Other non-refundable payments to the Company under this arrangement may include: (i) payments for research and development services, (ii) payments for the supply of clinical product, (iii) payments for the supply of commercial product, (iv) payments based on the achievement of certain development, regulatory, commercial, and sales-based milestones and (v) royalties on product sales.

The Company evaluates multiple-element arrangements based on the guidance in FASB ASC Topic 605-25, Revenue Recognition-Multiple-Element Arrangements (“ASC 605-25”). Pursuant to this guidance, the Company identifies the deliverables included in the arrangement and determines: (1) whether the individual deliverables have value to the customer on a standalone basis and represent separate units of accounting or whether they must be accounted for as a combined unit of accounting; and (2) if the arrangement includes a general right of return relative to the delivered item. This evaluation requires management to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer on a standalone basis and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in the control of the Company. In assessing whether an item has standalone value, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner, the retention of any key rights by the Company, and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can use the other deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s).

In situations where the Company has identified multiple units of accounting, the arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. The Company determines the selling price of a unit of accounting following the hierarchy of evidence prescribed by ASC 605-25. Accordingly, the Company determines the estimated selling price for units of accounting within each arrangement using vendor-specific objective evidence (“VSOE”) of selling price, if available, third-party evidence (“TPE”) of selling price if VSOE is not available, or best estimate of selling price (“BESP”) if neither VSOE nor TPE is available.

Then, the applicable revenue recognition criteria in ASC 605-25 are applied to each of the separate units of accounting to determine the appropriate period and pattern of recognition. The Company recognizes arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605-25 are satisfied for that particular unit of accounting. The Company will recognize as revenue, upon delivery, arrangement consideration attributed to licenses that have standalone value from the other deliverables to be provided in an arrangement. For licenses that do not have standalone value from the other deliverables to be provided in an arrangement over the Company’s estimated performance period as the arrangement would be accounted for as a single unit of accounting.

The Company recognizes arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605-25 are satisfied for that particular unit of accounting. The Company will recognize as revenue arrangement consideration attributed to licenses that have standalone value from the other deliverables to be provided in an arrangement upon delivery. The Company will recognize as revenue arrangement consideration attributed to licenses that do not have standalone value from the other deliverables to be provided in an arrangement over the Company’s estimated performance period as the arrangement would be accounted for as a single unit of accounting.

If there is no discernible pattern of performance and/or objectively measurable performance measures do not exist, then the Company recognizes revenue under the arrangement for the single unit of accounting on a straight-line basis over the period the Company is expected to complete its performance obligations. Alternatively, if the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance measures exist, then the Company recognizes revenue under the arrangement using the proportional performance method. Revenue recognized is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the straight-line method or proportional performance method, as applicable.

At the inception of an arrangement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. The Company recognizes revenue associated with substantive milestones in accordance with FASB ASC Topic 605-28, Revenue Recognition-Milestone Method upon successful accomplishment of each milestone, assuming all other revenue recognition criteria are met. Milestones that are not considered substantive would be recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria are met.

The Company will recognize royalty revenue in the period of sale of the related product(s), based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met.

Refer to footnote 10 for further information related to the Company’s collaboration and license agreement with Nestec, Ltd.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Warrant to Purchase Convertible Preferred Stock

The Company classified a warrant to purchase shares of its Series A-2 convertible preferred stock as a liability on its consolidated balance sheets as this warrant was a free-standing financial instrument that could have required the Company to transfer assets upon exercise. The warrant was initially recorded at fair value on date of grant, and it was subsequently remeasured to fair value at each balance sheet date. Changes in fair value of the warrant were recognized as a component of other income (expense), net in the consolidated statement of operations and comprehensive loss. The Company continued to adjust the liability for changes in fair value until the warrant became a warrant to purchase common stock in connection with the IPO.

The Company used the Black-Scholes option-pricing model, which incorporates assumptions and estimates, to value the preferred stock warrant. The Company assessed these assumptions and estimates on a quarterly basis as additional information impacting the assumptions was obtained. Estimates and assumptions impacting the fair value measurement included the fair value per share of the underlying Series A-2 convertible preferred stock, the remaining contractual term of the warrant, the risk-free interest rate, the expected dividend yield and the expected volatility of the price of the underlying preferred stock. The Company determined the fair value per share of the underlying preferred stock by taking into consideration the most recent sales of its convertible preferred stock, results obtained from third-party valuations and additional factors that were deemed relevant. The Company historically has been a private company and lacks company-specific historical and implied volatility information of its stock. Therefore, it estimated its expected stock volatility based on the historical volatility of publicly traded peer companies for a term equal to the remaining contractual term of the warrant. The risk-free interest rate was determined by reference to the U.S. Treasury yield curve for time periods approximately equal to the remaining contractual term of the warrant. Expected dividend yield was based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

Segment Data

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing Ecobiotic microbiome therapeutics to treat dysbiosis in the colonic microbiome. Revenue to date has been generated solely through the Company's collaboration with Nestle Health Science, all of which has been earned in the United States. All tangible assets are held in the United States

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. There was no difference between net loss and comprehensive loss for the year ended December 31, 2014. For the years ended December 31, 2016 and 2015, other comprehensive income (loss) consisted of changes in unrealized gains (losses) from available-for-sale investments.

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 Company applies the two-class method to calculate its basic and diluted net loss per share attributable to common stockholders, as its convertible preferred stock, which converted to Common Stock upon completion of the listing of the Company’s common stock on the NASDAQ on June 26, 2015, and common stock are participating securities. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to common stockholders. However, the two-class method does not impact the net loss per share of common stock as the Company was in a net loss position for each of the periods presented and preferred stockholders do not participate in losses.

The Company’s convertible preferred stock contractually entitles the holders of such shares to participate in dividends but does not contractually require the holders of such shares to participate in losses of the Company. Similarly, restricted stock awards 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 awards 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.

Recently Issued and Adopted Accounting Pronouncements

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. In August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which delayed the effective date of the new standard from January 1, 2017 to January 1, 2018. The FASB also agreed to allow entities to choose to adopt the standard as of the original effective date. In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations, which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies how a company identifies promised goods or services and clarifies whether an entity’s promise to grant a license provides a customer with either a right to use the entity’s intellectual property (which is satisfied at a point in time) or a right to access the entity’s intellectual property (which is satisfied over time). In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients related to disclosures of remaining performance obligations, as well as other amendments to guidance on collectibility, non-cash consideration and the presentation of sales and other similar taxes collected from customers. In December 2016 the FASB issued ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, which amends certain narrow aspects of the guidance issued in ASU 2014-09 including guidance related to the disclosure of remaining performance obligations and prior-period performance obligations, as well as other amendments to the guidance on loan guarantee fees, contract costs, refund liabilities, advertising costs and the clarification of certain examples. We are currently evaluating the method of adoption and the potential impact that Topic 606 may have on the Company’s financial position and results of operation.

In August 2014, the FASB issued guidance that explicitly requires a company’s management to assess an entity’s ability to continue as a going concern and to provide related footnote disclosures in certain circumstances. The standard was effective for us on December 31, 2016. The adoption of this standard did not have a material impact on our consolidated financial statements and related disclosures.

In May 2015, the FASB issued ASU 2015-07, Fair Value Measurement (Topic 820): Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent). The new standard removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the net asset value per share practical expedient. The new standard became effective for us on January 1, 2016. Refer to the Fair Value Measurements significant accounting policy for the impact of this change.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e. lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. ASC 842 supersedes the previous leases standard, ASC 840 Leases. The standard is effective on January 1, 2019, with early adoption permitted. The Company is in the process of evaluating the impact of this new guidance.

In March 2016, the FASB issued ASU 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, which amends the accounting for employee share-based payment transactions to require recognition of the tax effects resulting from the settlement of stock-based awards as income tax expense or benefit in the income statement in the reporting period in which they occur. In addition, the ASU requires that all tax-related cash flows resulting from share-based payments, including the excess tax benefits related to the settlement of stock-based awards, be classified as cash flows from operating activities in the statement of cash flows. The ASU also requires that cash paid by directly withholding shares for tax withholding purposes be classified as a financing activity in the statement of cash flows. In addition, the ASU also allows companies to make an accounting policy election to either estimate the number of awards that are expected to vest, consistent with current U.S. GAAP, or account for forfeitures when they occur. The Company has elected to early adopt ASU 2016-09 for the year ended December 31, 2016. The adoption of this standard did not have a material impact on our consolidated financial statements.

In August 2016, the FASB issued ASU No. 2016-15, Classification of Certain Cash Receipts and Cash Payments. The new standard addresses specific cash flow issues with the objective of reducing existing diversity in practice. The new standard will be effective for the Company on January 1, 2018. The Company is in the process of evaluating the impact of this new guidance.

In November 2016, the FASB issued ASU 2016-18, Restricted Cash. The new standard requires restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the total beginning and ending amounts for the periods shown on the statement of cash flows. The new standard will be effective for the Company on January 1, 2018. The Company is in the process of evaluating the impact of this new guidance.

Fair Value of Financial Assets and Liabilities

12 Months Ended

Dec. 31, 2016

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities

3.	Fair Value of Financial Assets and Liabilities

The following tables present information about the Company’s assets and liabilities as of December 31, 2016 and 2015 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:

	Fair Value Measurements as of December 31, 2016 Using:
	Level 1		Level 2		Level 3		Not Subject to Leveling ⁽¹⁾		Total
Assets:
Cash Equivalents	$	—	$	4,740	$	—	$	1,567	$	6,307
Repurchase Agreements		—		7,000		—		—		7,000
Investments:
Commercial Paper		—		19,689		—		—		19,689
Certificates of Deposit		—		10,629		—		—		10,629
Corporate Bonds		—		94,609		—		—		94,609
Government Securities		—		33,466		—		—		33,466
Treasury Bonds		—		17,063		—		—		17,063
	$	—	$	187,196	$	—	$	1,567	$	188,763

⁽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.

	Fair Value Measurements as of December 31, 2015 Using:
	Level 1		Level 2		Level 3		Not Subject to Leveling ⁽¹⁾		Total
Assets:
Cash Equivalents	$	—	$	11,952	$	—	$	11,173	$	23,125
Repurchase Agreements		—		20,000		—		—		20,000
Investments:
Commercial Paper		—		64,820		—		—		64,820
Corporate Bonds		—		46,490		—		—		46,490
Government Securities		—		15,819		—		—		15,819
Treasury Bonds		—		4,020		—		—		4,020
	$	—	$	163,101	$	—	$	11,173	$	174,274

⁽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.

As of December 31, 2016, the Company’s cash equivalents consisted of money market funds, corporate bonds, certificates of deposits, and repurchase agreements with original maturities of less than 90 days from the date of purchase and were valued based on Level 2 inputs. Repurchase agreements are agreements with banks to repurchase notes that are collateralized by U.S. government securities. All repurchase agreements have overnight maturities.

As of December 31, 2015, the Company’s cash equivalents consisted of money market funds, corporate bonds, commercial paper, and repurchase agreements with original maturities of less than 90 days from the date of purchase and were valued based on Level 2 inputs. Repurchase agreements are agreements with banks to repurchase notes that are collateralized by U.S. government securities.

The fair value of the Company’s investments, which consisted of corporate bonds, commercial paper, certificates of deposit, government securities, and treasury bonds as of December 31, 2016 and 2015, were determined using Level 2 inputs. During the years ended December 31, 2016 and 2015, there were no transfers between Level 1, Level 2 and Level 3.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Investments

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

Property Plant And Equipment [Abstract]

4.	Investments

As of December 31, 2016 and 2015, the fair value of available-for-sale investments by type of security was as follows:

	December 31, 2016
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial Paper	$	19,631	$	58	$	—		$	19,689
Certificates of Deposit		10,629		—		—			10,629
Corporate Bonds		94,764		—		(155	)		94,609
Government Securities		33,513		—		(47	)		33,466
Treasury Bonds		17,066		1		(4	)		17,063
	$	175,603	$	59	$	(206	)	$	175,456

	December 31, 2015
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial Paper	$	64,733	$	87	$	—		$	64,820
Corporate Bonds		46,538		—		(48	)		46,490
Government Securities		15,823		—		(4	)		15,819
Treasury Bonds		4,022		—		(2	)		4,020
	$	131,116	$	87	$	(54	)	$	131,149

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.

As of December 31, 2015, the Company’s corporate bonds, commercial paper, government securities and treasury bonds had remaining maturities of less than 12 months.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2016

Property and Equipment, Net

5.	Property and Equipment, Net

Property and equipment, net consisted of the following:

	December 31, 2016			December 31, 2015
Laboratory equipment	$	10,711		$	4,370
Computer equipment		1,335			408
Furniture and office equipment		1,010			285
Leasehold improvements		27,807			1,856
Construction in progress		442			1,843
		41,305			8,762
Less: Accumulated depreciation and amortization		(5,180	)		(1,011	)
	$	36,125		$	7,751

Depreciation and amortization expense was $4,205, $728 and $190 for the years ended December 31, 2016, 2015 and 2014, respectively.

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2016

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:

	December 31, 2016		December 31, 2015
Development and clinical manufacturing costs	$	3,350	$	1,436
Payroll and payroll-related costs		3,698		2,756
Professional fees		448		184
Facility and other		3,316		1,147
	$	10,812	$	5,523

Preferred Stock Warrant Liability

12 Months Ended

Dec. 31, 2016

Class Of Stock Disclosures [Abstract]

Preferred Stock Warrant Liability

7.	Preferred Stock Warrant Liability

In September 2013, the Company issued a warrant to purchase 92,127 shares of Series A-2 convertible preferred stock in connection with the loan security agreement. The warrant was immediately exercisable at an exercise price of $1.78 per share and had a contractual term of ten years from issuance. The fair value of the warrant at issuance was estimated to be $156 and was recorded as a debt discount and as a preferred stock warrant liability.

The Company classified the warrant to purchase shares of its Series A-2 convertible preferred stock as a liability on its consolidated balance sheets and subsequently re-measured to fair value at each balance sheet date. Changes in fair value of the warrant were recognized as a component of other income (expense), net, in the consolidated statement of operations and comprehensive loss.

The Company recorded losses of $7 and $1,418 for the years ended December 31, 2015 and 2014, respectively, to reflect the change in fair value of this preferred stock warrant.

The following assumptions and inputs were used in determining the fair value of the preferred stock warrant liability valued using the Black-Scholes option-pricing model:

	Year Ended December 31,
	2015			2014
Risk-free interest rate		2.40	%		2.17	%
Expected term (in years)		8.2			8.7
Expected volatility		91.2	%		84.0	%
Expected dividend yield		0	%		0	%
Fair value of Series A-2 convertible preferred stock	$	17.26		$	17.18

The following table provides a rollforward of the fair value of the Company’s preferred stock warrant liability:

	Fair Value
Balance as of December 31, 2013		164
Loss on revaluation		1,418
Balance as of December 31, 2014	$	1,582
Loss on revaluation		7
Reclassification to stockholders’ equity		(1,589	)
Balance as of December 31, 2015	$	—

In connection with the automatic conversion of the Company’s convertible preferred stock, which occurred upon the listing of the Company’s common stock on the NASDAQ on June 26, 2015, the preferred stock warrant became a warrant to purchase common stock. The Company performed the final mark to market adjustment on the preferred stock warrant using the fair value of the underlying common shares of $18.00 per share on June 26, 2015 and recorded the change in fair value in other income (expense), net in the consolidated statement of operations and comprehensive loss. The preferred stock warrant liability was then reclassified to additional paid-in-capital as it became a warrant to purchase common stock.

On August 17, 2015, the common stock warrant was exercised in full at an exercise price of $1.78 per share of common stock. The Company received proceeds of $164 in connection with the exercise of the common stock warrant.

There was no balance related to the preferred stock warrant liability as of December 31, 2016 and 2015.

Convertible Preferred Stock

12 Months Ended

Dec. 31, 2016

Equity [Abstract]

Convertible Preferred Stock

8.	Convertible Preferred Stock

On July 1, 2015, in connection with the closing of the IPO, the Company effected its Restated Certificate of Incorporation, which authorizes the Company to issue 10,000,000 shares of preferred stock, $0.001 par value per share.

Stockholders’ Equity Common Stock

12 Months Ended

Dec. 31, 2016

Equity [Abstract]

Stockholders’ Equity Common Stock

9.	Stockholders’ Equity Common Stock

On July 1, 2015, the Company completed an IPO, and issued and sold 8,545,138 shares of common stock at a public offering price of $18.00 per share, resulting in net proceeds of approximately $139,267 after deducting underwriting discounts and commissions and other offering expenses totaling $3,748. The shares issued upon closing of the IPO included 1,114,583 shares of the Company’s common stock, which were sold to the underwriters pursuant to the full exercise of their option to purchase additional shares of common stock. Upon the listing of the Company’s common stock on the NASDAQ on June 26, 2015, all outstanding shares of the Company’s convertible preferred stock automatically converted into 22,866,987 shares of the Company’s common stock.

As of December 31, 2014, the Company’s Amended and Restated Certificate of Incorporation, as further amended, authorized the Company to issue 38,000,000 shares of common stock, $0.001 par value per share. On July 1, 2015, in connection with the closing of the IPO, the Company effected its Restated Certificate of Incorporation, which authorizes the Company to issue 200,000,000 shares of common stock, $0.001 par value per share.

Common Stock Warrants

In June 2014, the Company entered into a research agreement with the Mayo Foundation for Medical Education and Research (“Mayo”) under which the Company acquired a license to intellectual property. In exchange for the license, the Company issued to Mayo a warrant to purchase 454,545 shares of common stock at an exercise price of $0.01 per share, which was immediately exercisable. Upon issuance of the warrant, the Company recorded research and development expense of $317 for the fair value of the warrant, determined using the following assumptions in the Black-Scholes option-pricing model: expected volatility of 86.0%, risk-free interest rate of 2.3%, expected term of seven years (equaling the contractual term of the warrant) and no expected dividends. Because this warrant was indexed to the Company’s stock and could only be settled by gross physical delivery of shares the Company determined that this warrant qualified for equity classification. This warrant was exercised on April 29, 2015.

The Company also issued to Mayo an additional warrant (the “performance warrant”) to purchase up to 284,090 shares of common stock at an exercise price equal to the per share price at which the Company most recently sold shares of its preferred stock. The performance warrant was exercisable for a number of shares to be determined by the Company’s board of directors from time to time, upon the achievement by Mayo of specified milestones. The performance warrant provided for termination upon the closing of an initial public offering by the Company. The IPO closed prior to any probable achievement of the specified milestones, therefore, the warrant terminated and the Company did not record any expense for the performance warrant from the date of issuance through the closing of the IPO.

2012 Stock Incentive Plan

The Company’s 2012 Stock Incentive Plan, as amended, (the “2012 Plan”) provides for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company. The 2012 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. The Company generally grants stock-based awards with service conditions only (“service-based” awards).

Stock options granted under the 2012 Plan generally vest over four years and expire after ten years, although options have been granted with vesting terms less than four years.

The total number of shares of common stock that may be issued under the 2012 Plan was 1,261,836 shares as of December 31, 2013. In May 2014, the Company effected an increase in the number of shares of common stock reserved for issuance under the 2012 Plan to 3,561,836 shares. In December 2014, the Company effected an increase in the number of shares of common stock reserved for issuance under the 2012 Plan to 3,608,029 shares. The total number of shares of common stock that may be issued under the 2012 Plan was 3,608,029 shares as of December 31, 2014. In March 2015, the Company effected an increase in the number of shares of common stock reserved for issuance under the 2012 Plan to 4,309,653 shares. As of December 31, 2016, there were no shares available for future grant under the 2012 Plan.

As required by the 2012 Plan, the exercise price for stock options granted is not to be less than the fair value of common shares as determined by the Company as of the date of grant. The Company values its common stock by taking into consideration its most recently available valuation of common shares performed by management and the board of directors as well as additional factors which may have changed since the date of the most recent contemporaneous valuation through the date of grant.

2015 Incentive Award Plan

On June 16, 2015, the Company’s stockholders approved the 2015 Incentive Award Plan (the “2015 Plan”), which became effective on June 25, 2015. The 2015 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. The number of shares initially reserved for issuance under the 2015 Plan is the sum of (i) 2,200,000 shares of common stock and (ii) the number of shares subject to awards outstanding under the 2012 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company on or after the effective date of the 2015 Plan. In addition, the number of shares of common stock that may be issued under the 2015 Plan is subject to increase on the first day of each calendar year, beginning in 2016 and ending in 2025, equal to the lesser of (i) 4% of the number of shares of the Company’s common stock outstanding on the last day of the preceding applicable calendar year and (ii) an amount determined by the Company’s board of directors. As of December 31, 2016, there were 1,352,907 shares available for future grant under the 2015 Plan.

2015 Employee Stock Purchase Plan

On June 16, 2015, the Company’s stockholders approved the 2015 Employee Stock Purchase Plan (the “ESPP”), which became effective on June 25, 2015. A total of 365,000 shares of common stock were reserved for issuance under the ESPP. In addition, the number of shares of common stock that may be issued under the ESPP will automatically increase on the first day of each calendar year, beginning in 2016 and ending in 2025, by an amount equal to the least of (i) 400,000 shares, (ii) 1% of the number of shares of the Company’s common stock outstanding on the last day of the applicable preceding calendar year and (iii) an amount determined by the Company’s board of directors. Offering periods under the ESPP will commence when determined by the plan administrator. As of December 31, 2016, there were no shares issued under the ESPP.

Stock Option Valuation

The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors were as follows, presented on a weighted average basis:

	Year Ended December 31,
	2016			2015			2014
Risk-free interest rate		1.54	%		1.80	%		1.83	%
Expected term (in years)		6.0			6.0			6.0
Expected volatility		84.2	%		81.4	%		83.5	%
Expected dividend yield		0	%		0	%		0	%

Stock Options

The following table summarizes the Company’s stock option activity for the twelve months ended December 31, 2016:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2015		5,026,246		$	8.01		8.70	$	136,945
Granted		1,695,125			26.04
Exercised		(1,273,736	)		1.68
Forfeited		(378,502	)		24.93
Outstanding as of December 31, 2016		5,069,133		$	14.36		8.26	$	16,736
Options vested and expected to vest as of December 31, 2016		5,069,133		$	14.36		8.26	$	16,736
Options exercisable as of December 31, 2016		1,686,284		$	8.05	7.62		$	9,048

The weighted average grant-date fair value of stock options granted during the years ended December 31, 2016, 2015 and 2014 was $18.45, $14.56, and $4.25 per share, respectively. The total intrinsic value of stock options exercised during the years ended December 31, 2016, 2015, and 2014 was $34,871, $4,125, and $512.

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock.

The Company granted performance-based stock options to certain employees. These stock options were exercisable only upon achievement of specified performance targets. During the year ended December 31, 2016, the Company determined that the achievement of these specified performance targets occurred. Upon achievement of the performance targets, 60,000 options became immediately vested. The Company recorded stock based compensation expense of $235 during the year ended December 31, 2016 related to these awards. The grant date fair value of these awards was $3.92 per share.

As of December 31, 2016 and 2015, there were outstanding unvested service-based stock options held by non-employees for the purchase of 63,375 and 27,750 shares, respectively, of common stock.

Restricted Stock Units

The Company has granted restricted stock units with time-based vesting conditions. The table below summarizes the Company’s restricted stock activity for the twelve months ended December 31, 2016:

	Number of Shares		Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2015		—	$	—
Granted		115,500	$	9.78
Vested		—	$	—
Unvested restricted stock units as of December 31, 2016		115,500	$	9.78

The aggregate intrinsic value of restricted stock units that vested during the years ended December 31, 2016, 2015 and 2014 was $0, $1,508, and $684, respectively.

Stock-based Compensation

The Company recorded stock-based compensation expense related to stock options and restricted stock units in the following expense categories of its consolidated statements of operations and comprehensive loss:

	Year Ended December 31,
	2016		2015		2014
Research and development expenses	$	8,310	$	5,297	$	1,068
General and administrative expenses		8,547		4,397		1,000
	$	16,857	$	9,694	$	2,068

As of December 31, 2016, the Company had an aggregate of $35,405 of unrecognized stock- based compensation cost, which is expected to be recognized over a weighted average period of 2.66 years.

Collaboration Revenue	12 Months Ended
Collaboration Revenue	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Revenue	10. Collaboration Revenue Nestec Ltd. In January 2016 the Company entered into the License Agreement with NHS, an affiliate of Nestlé Health Science US Holdings, Inc., a significant stockholder of the Company, for the development and commercialization of certain product candidates in development for the treatment and management of CDI and IBD, including ulcerative colitis and Crohn’s disease. The License Agreement will support 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. Under the License Agreement, the Company’s and NHS’ development activities will be governed by global and regional development plans, including the conduct of additional clinical studies. The Company has agreed to manufacture and supply NHS Collaboration Products to support development and commercialization of NHS Collaboration Products in the licensed fields and in the Licensed Territory. NHS will have the right to obligate the Company to transfer technology necessary to manufacture Collaboration Products in the event that the Company materially fails to meet its supply commitments to NHS under the commercial supply agreement. The Company has also agreed to use diligent efforts to develop NHS Collaboration Products under a global development plan and to obtain approval for such NHS Collaboration Products in the European Union. 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. For the development of NHS Collaboration Products for IBD under a global development plan, the Company agreed to pay the costs of clinical trials of such products up to and including Phase 2 clinical trials, and 67% of the costs for Phase 3 and other clinical trials of such products, with NHS bearing the remaining 33% of such costs. For other clinical development of NHS Collaboration Products for IBD, the Company agreed to pay the costs of such activities to support approval in the United States and Canada, and NHS agreed to bear the cost of such activities to support approval of NHS Collaboration Products in the Licensed Territory. With respect to development of NHS Collaboration Products for CDI under a global development plan, the Company agreed to pay all costs of an ongoing Phase 2 clinical trial for SER-109 and of Phase 3 clinical trials for SER-109. The Company agreed to bear all costs of conducting any Phase 1 or Phase 2 clinical trials under a global development plan for NHS Collaboration Products other than SER-109 for CDI. The Company agreed to pay 67% and NHS agreed to pay 33% of other costs of Phase 3 clinical trials conducted for NHS Collaboration Products other than SER-109 for CDI under a global development plan. For other clinical development of NHS Collaboration Products for CDI, the Company agreed to pay costs of such development activities to support approval in the United States and Canada, and NHS agreed to bear the cost of such activities to support approval of NHS Collaboration Products in the Licensed Territory. The License Agreement continues in effect until terminated by either the Company or NHS on the following bases: (i) NHS may terminate the License Agreement in the event of serious safety issues related to any of the NHS Collaboration Products; (ii) the Company may terminate the License Agreement if NHS challenges the validity or enforceability of any of the Company’s licensed patents; and (iii) either the Company or NHS may terminate the License Agreement in the event of the other party’s uncured material breach or insolvency. Upon termination of the License Agreement, all licenses granted to NHS by the Company will terminate, and all rights in and to the NHS Collaboration Products in the Licensed Territory will revert to the Company. If the Company commits a material breach of the License Agreement, NHS may elect not to terminate the License Agreement but instead apply specified adjustments to its payment obligations and other terms and conditions of the License Agreement. The License Agreement contains customary representations and warranties, intellectual property protection provisions, certain indemnification rights in favor of each party and customary confidentiality provisions and limitations of liability. At the inception of the License Agreement, the Company identified the following deliverables: (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. The Company also identified a contingent deliverable, the obligation to perform manufacturing services to provide commercial supply if commercialization occurs, which is contingent upon regulatory approval. This contingent deliverable has been excluded from the initial allocation and will be treated as a separate unit of accounting when and if delivered. The Company concluded that none of the four deliverables identified at the inception of the License Agreement has standalone value from the other undelivered elements. Accordingly, all deliverables represent a single unit of accounting. All consideration received relating to the four identified deliverables that comprise the single unit of accounting will be recognized over the period of performance. The period of performance will be through the completion of development services for the NHS Collaboration Products which has been estimated to be ten years. The Company will periodically review and, if necessary, revise the estimated development period. The Company will recognize revenue utilizing a time-based proportional performance model where revenue related to each payment is recognized over the ten year performance period. As of December 31, 2016, the only consideration that is fixed and determinable is the non-refundable upfront payment of $120,000 and $580 for the reimbursement of development services since the inception of the arrangement. For additional consideration that could be received for research and development services and/or manufacturing services for clinical supply, the Company will recognize a cumulative catch-up for the amount of time that has elapsed and spread the unrecognized portion over the remaining performance period. Development and regulatory milestones that involve substantial effort on the Company’s part and the achievement of which are not considered probable at the inception of the License Agreement are considered substantive milestones, and will be recognized in their entirety in the period in which the milestone is achieved, assuming all other revenue recognition criteria are met. All commercial milestones will be recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met. The Company has evaluated all of the milestones that may be received in connection with the License Agreement with NHS. In evaluating if a milestone is substantive, the Company assesses whether, (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. All development, approval and commercialization milestones that may be received under the License Agreement are considered substantive on the basis of the contingent nature of the milestone. The Company has specifically reviewed factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the milestone as well as the level of effort and investment required. Accordingly, such amounts will be recognized as revenue in full in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. 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. The Company recognizes revenue associated with substantive milestones in accordance with FASB ASC Topic 605-28, Revenue Recognition-Milestone Method. The $10,000 was recognized in full as related party collaboration revenue during the year ended December 31, 2016. Royalties will be recorded as revenue in the period they are earned assuming all other revenue recognition criteria are met. During the year ended December 31, 2016, the Company recognized $21.8 million of related party revenue associated with the License Agreement. As of December 31, 2016, there was $108.8 million 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 twelve months. All costs associated with the License Agreement are recorded in research and development expense in the consolidated statements of operations and comprehensive loss.

Net Loss per Share

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Net Loss per Share

11.	Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:

	Year Ended December 31,
	2016			2015			2014
Numerator:
Net loss	$	(91,579	)	$	(54,780	)	$	(16,709	)
Accretion of convertible preferred stock to redemption value		—			—			(1,291	)
Net loss attributable to common stockholders	$	(91,579	)	$	(54,780	)	$	(18,000	)
Denominator:
Weighted average common shares outstanding, basic and diluted		39,846,928			23,532,400			6,748,037
Net loss per share attributable to common stockholders, basic and diluted	$	(2.30	)	$	(2.33	)	$	(2.67	)

The Company’s potential dilutive securities, which include stock options, unvested restricted common stock, convertible preferred stock and warrants to purchase convertible preferred stock or common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. 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:

	Year Ended December 31,
	2016		2015		2014
Stock options to purchase common stock		5,069,133		5,026,246		3,579,342
Unvested restricted stock units		115,500		—		—
Unvested restricted common stock		—		—		52,500
Warrants for the purchase of convertible preferred stock		—		—		92,127
Warrants for the purchase of common stock		—		—		738,635
Convertible preferred stock (as converted to common stock)		—		—		21,478,098
		5,184,633		5,026,246		25,940,702

Commitments and Contingencies

12 Months Ended

Dec. 31, 2016

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

12.	Commitments and Contingencies

Leases

The Company previously leased office and laboratory space with a lease term expiring in January 2018 and no extension periods. In May 2016, upon mutual agreement with the landlord, the Company accelerated the termination of the operating lease to June 30, 2016. Upon termination of the lease, the Company recorded a benefit to rent expense of $136 to write off amounts previously recorded as deferred rent. The outstanding security deposit of $119, which was secured by a cash collateralized letter of credit, was released in September 2016.

On April 1, 2015, the Company entered into a lease for additional office and laboratory space with a term expiring in April 2020.

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 December 31, 2016, we recorded a lease incentive obligation of $12,080. During the year ended December 31, 2016, we amortized $429 of this lease incentive obligation as a reduction to rent expense.

During the years ended December 31, 2016, 2015 and 2014, the Company recognized $3,826 , $1,246, and $543, respectively, of rental expense related to office and laboratory space.

Future minimum lease payments for these operating leases as of December 31, 2016 are as follows:

Year Ending December 31,
2017	$	5,978
2018		6,158
2019		6,342
2020		6,120
2021		6,222
2022 and thereafter		11,529
Total	$	42,349

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 December 31, 2016 or 2015.

Legal Proceedings

On September 28, 2016, a purported stockholder of the Company filed a putative class action lawsuit in the U.S. District Court for the District of Massachusetts against the Company entitled Mariusz Mazurek v. Seres Therapeutics, Inc., et.al. and on February 12, 2017, the Company received an amended complaint. The lawsuit alleges violations of Sections 10(b), 20(a) and Rule 10b-5 of the Securities Exchange Act of 1934, as amended, by making allegedly false and misleading statements and omissions about the Company’s clinical trials for its product candidate SER-109 in the Company’s public disclosures between June 25, 2015 and July 29, 2016. The lawsuit seeks, among other things, damages in connection with the Company’s allegedly inflated stock price between June 25, 2015 and July 29, 2016 as a result of those allegedly false and misleading statements, as well as interest, attorneys’ fees and costs. The Company can make no assurances as to the time or resources that will need to be devoted to this lawsuit or its final outcome, or the impact, if any, of this lawsuit or any proceedings on its business, financial condition, results of operations and cash flows. While the Company is vigorously defending against all claims asserted, this litigation could result in substantial costs to the Company and a diversion of the Company’s management’s attention and resources, which could harm its business. In addition, the uncertainty of the pending lawsuit or potential filing of additional lawsuits could lead to more volatility and a reduction in the Company’s stock price. Given the early stage of the litigation, at this time the Company is unable to reasonably estimate possible losses or form a judgment that an unfavorable outcome is either probable or remote. It is not currently possible to assess whether or not the outcome of these proceedings may have a material adverse effect on the Company.

Income Taxes

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Income Taxes

13.	Income Taxes

During the years ended December 31, 2016, 2015 and 2014, the Company recorded no income tax benefits for the net operating losses incurred in each year or interim period, due to its uncertainty of realizing a benefit from those items.

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2016			2015			2014
Federal statutory income tax rate		(34.0	)%		(34.0	)%		(34.0	)%
Research and development tax credits		(8.8	)		(5.7	)		(3.8	)
State taxes, net of federal benefit		(5.8	)		(5.3	)		(5.3	)
Stock-based compensation		(6.3	)		4.1			2.3
Revaluation of preferred stock warrant liability		—			—			3.3
Other		0.1			0.3			0.2
Change in deferred tax asset valuation allowance		54.8			40.6			37.3
Effective income tax rate		—	%		—	%		—	%

Net deferred tax assets as of December 31, 2016 and 2015 consisted of the following:

	December 31,
	2016			2015
Deferred tax assets:
Net operating loss carryforwards	$	18,481		$	25,293
Research and development tax credit carryforwards		14,991			4,180
Capitalized organization costs		483			527
Stock-based compensation expense		5,624			1,897
Charitable Contributions		6			5
Deferred Revenue		42,742			—
Accrued expenses		5,560			977
Capitalized research and development expenses		115			126
Total deferred tax assets	$	88,002			33,005
Deferred tax liabilities:
Depreciation and amortization		(5,008	)		(228	)
Total deferred tax liabilities		(5,008	)		(228	)
Valuation allowance	$	(82,994	)		(32,777	)
Net deferred tax assets	$	—		$	—

As of December 31, 2016, the Company had net operating loss carryforwards for federal and state income tax purposes of $47,165 and $46,296, respectively, which both begin to expire in 2031. As of December 31, 2016, the Company also had available research and development tax credit carryforwards for federal and state income tax purposes of $13,500 and $2,260, respectively, which begin to expire in 2031 and 2028, respectively. The federal research and development tax credits include an orphan drug credit carryforward of $8,473. Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period. Since our formation, we have raised capital through the issuance of capital stock on several occasions. These financings, combined with the purchasing shareholders' subsequent disposition of those shares, may have resulted in a change of control as defined by Section 382 or could result in a change of control in the future upon subsequent disposition. We conducted an analysis under Section 382 to determine if historical changes in ownership through August 31, 2015 would limit or otherwise restrict our ability to utilize these NOL and R&D credit carryforwards. As a result of this analysis, we do not believe there are any significant limitations on our ability to utilize these carryforwards. However, future changes in ownership after August 31, 2015 could affect the limitation in future years. Any limitation may result in expiration of a portion of the NOL or R&D credit carryforwards before utilization. At December 31, 2016, $20,211 of the federal net operating loss carryforwards, and $20,211 of the state net operating loss carryforwards relate to excess stock based compensation tax benefits for which the benefit will be recorded to additional paid-in capital when recognized. The Company early adopted ASU 2016-09, and as such, as of December 31, 2016, those amounts have been recorded as a deferred tax asset and offset by a valuation allowance.

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 December 31, 2016 and 2015. Management reevaluates the positive and negative evidence at each reporting period.

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2016, 2015 and 2014 related primarily to the increases in net operating loss carryforwards, research and development tax credit carryforwards and stock-based compensation were as follows:

	Year Ended December 31,
	2016			2015			2014
Valuation allowance at beginning of year	$	(32,777	)	$	(10,522	)	$	(4,294	)
Decreases recorded as benefit to income tax provision		—			—			—
Increases recorded to income tax provision		(50,217	)		(22,255	)		(6,228	)
Valuation allowance as of end of year	$	(82,994	)	$	(32,777	)	$	(10,522	)

During the year ended December 31, 2016, the Company was awarded a $0.9 million tax incentive for job creation from the Massachusetts Life Sciences Center. The program was established in 2008 in order to incentivize life sciences companies to create new sustained jobs in Massachusetts. Jobs must be maintained for at least five years, during which time the grant proceeds can be recovered by the Massachusetts Department of Revenue ("DOR") if the Company does not meet and maintain its job creation commitments. The award was received in 2016 and recognized as other income in the consolidated statement of operations. As of December 31, 2016, the Company determined that it did not satisfy the job creation commitments under the award, and the full amount of $0.9 million was reversed from other income and the award has been recorded as other current liabilities. The Company is currently evaluating future treatment of the award, pending further discussion with the Mass Life Sciences Center.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Data [Abstract]

Selected Quarterly Financial Data (Unaudited)

14.	Selected Quarterly Financial Data (Unaudited)

The following table contains quarterly financial information for 2016 and 2015. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period.

	2016
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Total
Collaboration revenue - related party ⁽¹⁾	$	2,710		$	3,004		$	13,015		$	3,037		$	21,766
Total operating expenses		22,626			31,144			32,110			28,725			114,605
Loss from operations		(19,916	)		(28,140	)		(19,095	)		(25,688	)		(92,839	)
Net loss		(19,704	)		(27,913	)		(18,688	)		(25,274	)		(91,579	)
Net loss per share applicable to common stockholders - basic and diluted	$	(0.50	)	$	(0.70	)	$	(0.46	)	$	(0.63	)	$	(2.30	)

	2015
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Total
Collaboration revenue - related party⁽¹⁾	$	—		$	—		$	—		$	—		$	—
Total operating expenses		8,167			12,340			14,561			19,788			54,856
Loss from operations		(8,167	)		(12,340	)		(14,561	)		(19,788	)		(54,856	)
Net loss		(7,971	)		(12,555	)		(14,620	)		(19,634	)		(54,780	)
Net loss per share applicable to common stockholders - basic and diluted	$	(1.15	)	$	(1.45	)	$	(0.38	)	$	(0.50	)	$	(2.33	)

(1)

Related Party Transactions

12 Months Ended

Dec. 31, 2016

Related Party Transactions

15.	Related Party Transactions

In October 2010, the Company entered into a services agreement with Flagship Ventures Management, Inc., an affiliate of one of its stockholders (and now known as Flagship Pioneering), Flagship Venture Funds, to provide general and administrative services to the Company, including the employer portions of employee health and dental benefit plans for Seres Therapeutics employees and consulting services. The Company made payments under the agreement of $ 17, $502, and $454 during the years ended December 31, 2016, 2015 and 2014, respectively. There were no amounts due to Flagship Pioneering, related to the services agreement as of December 31, 2016 and 2015.

As described in Note 10, 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 ulcerative colitis 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 year ended December 31, 2016, the Company recognized $21,766 of related party revenue associated with the License Agreement. As of December 31, 2016, there was $108,814 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 year ended December 31, 2016. There is $306 due from NHS as of December 31, 2016 for the reimbursement of development costs, which is classified as other current assets in the Company’s consolidated balance sheet.

401(k) Savings Plan

12 Months Ended

Dec. 31, 2016

Compensation And Retirement Disclosure [Abstract]

401(k) Savings Plan

16.	401(k) Savings Plan

The Company has a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Effective January 1, 2016, the Company has elected to match 50% of the first 6% of an employee’s deferral. Company contributions are expensed in the year for which they are declared. During the year ended December 31, 2016, the Company recorded expense of $457 for accrued 401(k) match contributions.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

The Company classifies its available-for-sale investments as current assets on the consolidated balance sheet if they mature within one year from the balance sheet date.

Concentration of Credit Risk and of Significant Suppliers

Fair Value Measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Deferred Offering Costs

Property and Equipment

Impairment of Long-Lived Assets

Research and Development Costs

Research Contract Costs and Accruals

Patent Costs

Accounting for Stock-Based Compensation

The Company recognizes adjustments to stock compensation expense for forfeitures as they occur.

Revenue Recognition

The Company currently generates its revenue through collaboration and license arrangements with strategic partners for the development and commercialization of product candidates.

•

Persuasive evidence of an arrangement exists

•

Delivery has occurred or services have been rendered

•

The seller’s price to the buyer is fixed or determinable

•

Collectability is reasonably assured

Collaboration Revenue

Refer to footnote 10 for further information related to the Company’s collaboration and license agreement with Nestec, Ltd.

Income Taxes

Warrant to Purchase Convertible Preferred Stock

Segment Data

Comprehensive Loss

Net Loss per Share

Recently Issued and Adopted Accounting Pronouncements

Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2016

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis

	Fair Value Measurements as of December 31, 2016 Using:
	Level 1		Level 2		Level 3		Not Subject to Leveling ⁽¹⁾		Total
Assets:
Cash Equivalents	$	—	$	4,740	$	—	$	1,567	$	6,307
Repurchase Agreements		—		7,000		—		—		7,000
Investments:
Commercial Paper		—		19,689		—		—		19,689
Certificates of Deposit		—		10,629		—		—		10,629
Corporate Bonds		—		94,609		—		—		94,609
Government Securities		—		33,466		—		—		33,466
Treasury Bonds		—		17,063		—		—		17,063
	$	—	$	187,196	$	—	$	1,567	$	188,763

⁽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.

	Fair Value Measurements as of December 31, 2015 Using:
	Level 1		Level 2		Level 3		Not Subject to Leveling ⁽¹⁾		Total
Assets:
Cash Equivalents	$	—	$	11,952	$	—	$	11,173	$	23,125
Repurchase Agreements		—		20,000		—		—		20,000
Investments:
Commercial Paper		—		64,820		—		—		64,820
Corporate Bonds		—		46,490		—		—		46,490
Government Securities		—		15,819		—		—		15,819
Treasury Bonds		—		4,020		—		—		4,020
	$	—	$	163,101	$	—	$	11,173	$	174,274

Investments (Tables)

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

Schedule of Fair Value of Available-for-Sale Investments by Type of Security

As of December 31, 2016 and 2015, the fair value of available-for-sale investments by type of security was as follows:

	December 31, 2016
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial Paper	$	19,631	$	58	$	—		$	19,689
Certificates of Deposit		10,629		—		—			10,629
Corporate Bonds		94,764		—		(155	)		94,609
Government Securities		33,513		—		(47	)		33,466
Treasury Bonds		17,066		1		(4	)		17,063
	$	175,603	$	59	$	(206	)	$	175,456

	December 31, 2015
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial Paper	$	64,733	$	87	$	—		$	64,820
Corporate Bonds		46,538		—		(48	)		46,490
Government Securities		15,823		—		(4	)		15,819
Treasury Bonds		4,022		—		(2	)		4,020
	$	131,116	$	87	$	(54	)	$	131,149

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2016

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consisted of the following:

	December 31, 2016			December 31, 2015
Laboratory equipment	$	10,711		$	4,370
Computer equipment		1,335			408
Furniture and office equipment		1,010			285
Leasehold improvements		27,807			1,856
Construction in progress		442			1,843
		41,305			8,762
Less: Accumulated depreciation and amortization		(5,180	)		(1,011	)
	$	36,125		$	7,751

Accrued Expenses and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2016

Payables And Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	December 31, 2016		December 31, 2015
Development and clinical manufacturing costs	$	3,350	$	1,436
Payroll and payroll-related costs		3,698		2,756
Professional fees		448		184
Facility and other		3,316		1,147
	$	10,812	$	5,523

Preferred Stock Warrant Liability (Tables)

12 Months Ended

Dec. 31, 2016

Class Of Stock Disclosures [Abstract]

Summary of Assumptions and Inputs Used in Determining Fair Value of Preferred Stock Warrant Liability Valued Using Black-Scholes Option-Pricing Model

The following assumptions and inputs were used in determining the fair value of the preferred stock warrant liability valued using the Black-Scholes option-pricing model:

	Year Ended December 31,
	2015			2014
Risk-free interest rate		2.40	%		2.17	%
Expected term (in years)		8.2			8.7
Expected volatility		91.2	%		84.0	%
Expected dividend yield		0	%		0	%
Fair value of Series A-2 convertible preferred stock	$	17.26		$	17.18

Summary of Rollforward of Fair Value of Preferred Stock Warrant Liability

The following table provides a rollforward of the fair value of the Company’s preferred stock warrant liability:

	Fair Value
Balance as of December 31, 2013		164
Loss on revaluation		1,418
Balance as of December 31, 2014	$	1,582
Loss on revaluation		7
Reclassification to stockholders’ equity		(1,589	)
Balance as of December 31, 2015	$	—

Stockholders’ Equity Common Stock (Tables)

12 Months Ended

Dec. 31, 2016

Equity [Abstract]

Summary of Fair Value of Stock Option

The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors were as follows, presented on a weighted average basis:

	Year Ended December 31,
	2016			2015			2014
Risk-free interest rate		1.54	%		1.80	%		1.83	%
Expected term (in years)		6.0			6.0			6.0
Expected volatility		84.2	%		81.4	%		83.5	%
Expected dividend yield		0	%		0	%		0	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the twelve months ended December 31, 2016:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2015		5,026,246		$	8.01		8.70	$	136,945
Granted		1,695,125			26.04
Exercised		(1,273,736	)		1.68
Forfeited		(378,502	)		24.93
Outstanding as of December 31, 2016		5,069,133		$	14.36		8.26	$	16,736
Options vested and expected to vest as of December 31, 2016		5,069,133		$	14.36		8.26	$	16,736
Options exercisable as of December 31, 2016		1,686,284		$	8.05	7.62		$	9,048

Summary of Restricted Stock Activity

The table below summarizes the Company’s restricted stock activity for the twelve months ended December 31, 2016:

	Number of Shares		Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2015		—	$	—
Granted		115,500	$	9.78
Vested		—	$	—
Unvested restricted stock units as of December 31, 2016		115,500	$	9.78

Summary of Stock Based Compensation Expense

	Year Ended December 31,
	2016		2015		2014
Research and development expenses	$	8,310	$	5,297	$	1,068
General and administrative expenses		8,547		4,397		1,000
	$	16,857	$	9,694	$	2,068

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Basic and Diluted Net Loss per Share Attributable to Common Stockholders

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:

	Year Ended December 31,
	2016			2015			2014
Numerator:
Net loss	$	(91,579	)	$	(54,780	)	$	(16,709	)
Accretion of convertible preferred stock to redemption value		—			—			(1,291	)
Net loss attributable to common stockholders	$	(91,579	)	$	(54,780	)	$	(18,000	)
Denominator:
Weighted average common shares outstanding, basic and diluted		39,846,928			23,532,400			6,748,037
Net loss per share attributable to common stockholders, basic and diluted	$	(2.30	)	$	(2.33	)	$	(2.67	)

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:

	Year Ended December 31,
	2016		2015		2014
Stock options to purchase common stock		5,069,133		5,026,246		3,579,342
Unvested restricted stock units		115,500		—		—
Unvested restricted common stock		—		—		52,500
Warrants for the purchase of convertible preferred stock		—		—		92,127
Warrants for the purchase of common stock		—		—		738,635
Convertible preferred stock (as converted to common stock)		—		—		21,478,098
		5,184,633		5,026,246		25,940,702

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2016

Commitments And Contingencies Disclosure [Abstract]

Summary of Future Minimum Lease Payments for Operating Leases

Future minimum lease payments for these operating leases as of December 31, 2016 are as follows:

Year Ending December 31,
2017	$	5,978
2018		6,158
2019		6,342
2020		6,120
2021		6,222
2022 and thereafter		11,529
Total	$	42,349

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of U.S Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2016			2015			2014
Federal statutory income tax rate		(34.0	)%		(34.0	)%		(34.0	)%
Research and development tax credits		(8.8	)		(5.7	)		(3.8	)
State taxes, net of federal benefit		(5.8	)		(5.3	)		(5.3	)
Stock-based compensation		(6.3	)		4.1			2.3
Revaluation of preferred stock warrant liability		—			—			3.3
Other		0.1			0.3			0.2
Change in deferred tax asset valuation allowance		54.8			40.6			37.3
Effective income tax rate		—	%		—	%		—	%

Schedule of Net Deferred Tax Assets

Net deferred tax assets as of December 31, 2016 and 2015 consisted of the following:

	December 31,
	2016			2015
Deferred tax assets:
Net operating loss carryforwards	$	18,481		$	25,293
Research and development tax credit carryforwards		14,991			4,180
Capitalized organization costs		483			527
Stock-based compensation expense		5,624			1,897
Charitable Contributions		6			5
Deferred Revenue		42,742			—
Accrued expenses		5,560			977
Capitalized research and development expenses		115			126
Total deferred tax assets	$	88,002			33,005
Deferred tax liabilities:
Depreciation and amortization		(5,008	)		(228	)
Total deferred tax liabilities		(5,008	)		(228	)
Valuation allowance	$	(82,994	)		(32,777	)
Net deferred tax assets	$	—		$	—

Summary of Changes In Valuation Allowance for Deferred Tax Assets

	Year Ended December 31,
	2016			2015			2014
Valuation allowance at beginning of year	$	(32,777	)	$	(10,522	)	$	(4,294	)
Decreases recorded as benefit to income tax provision		—			—			—
Increases recorded to income tax provision		(50,217	)		(22,255	)		(6,228	)
Valuation allowance as of end of year	$	(82,994	)	$	(32,777	)	$	(10,522	)

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Data [Abstract]

Schedule of Quarterly Financial Information

	2016
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Total
Collaboration revenue - related party ⁽¹⁾	$	2,710		$	3,004		$	13,015		$	3,037		$	21,766
Total operating expenses		22,626			31,144			32,110			28,725			114,605
Loss from operations		(19,916	)		(28,140	)		(19,095	)		(25,688	)		(92,839	)
Net loss		(19,704	)		(27,913	)		(18,688	)		(25,274	)		(91,579	)
Net loss per share applicable to common stockholders - basic and diluted	$	(0.50	)	$	(0.70	)	$	(0.46	)	$	(0.63	)	$	(2.30	)

	2015
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Total
Collaboration revenue - related party⁽¹⁾	$	—		$	—		$	—		$	—		$	—
Total operating expenses		8,167			12,340			14,561			19,788			54,856
Loss from operations		(8,167	)		(12,340	)		(14,561	)		(19,788	)		(54,856	)
Net loss		(7,971	)		(12,555	)		(14,620	)		(19,634	)		(54,780	)
Net loss per share applicable to common stockholders - basic and diluted	$	(1.15	)	$	(1.45	)	$	(0.38	)	$	(0.50	)	$	(2.33	)

(1)

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 02, 2015	Jun. 26, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 01, 2015
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporated year			Oct. 31, 2010
Entity incorporated state name			State of Delaware
Accumulated deficit			$ 174,191	$ 82,612
Cash, cash equivalents and investments			$ 229,995
Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock issued and sold	8,545,138			8,545,138	6,563
Net proceeds from issuance of common stock from IPO after deducting underwriting discounts and commissions	$ 139,267
Conversion of redeemable convertible preferred stock into common stock		22,866,987		22,866,987
Initial Public Offering ("IPO") [Member] \| Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Public offering price per share		$ 18.00				$ 18.00
Conversion of redeemable convertible preferred stock into common stock		22,866,987
Over-Allotment Option [Member] \| Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock issued and sold	1,114,583

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		1 Months Ended		12 Months Ended
	Jul. 02, 2015	Feb. 29, 2016	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Line Items]
Maximum maturity days for cash equivalents				90 days
Restricted cash				$ 1,400,000	$ 1,539,000
Deferred offering costs				0	$ 0
Reclassification of deferred offering costs to additional paid in capital	$ 3,748,000
Impairment losses on long lived assets				$ 0
Minimum percentage of likelihood of tax benefit being realized upon settlement				50.00%
Nestlé Health Science [Member]
Accounting Policies [Line Items]
Upfront non-refundable payment		$ 120,000,000	$ 120,000,000	$ 120,000,000
Laboratory Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset				5 years
Computer Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset				3 years
Furniture and Office Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset				3 years

Fair Value of Financial Assets and Liabilities - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)
$ in Thousands

Dec. 31, 2016

Dec. 31, 2015

Assets:

Cash Equivalents

$ 6,307

$ 23,125

Repurchase Agreements

7,000

20,000

Fair Value, Inputs, Level 2 [Member]

Total assets

188,763

174,274

Assets:

Cash Equivalents

4,740

11,952

Repurchase Agreements

7,000

20,000

Not Subject to Leveling [Member]

Total assets

187,196

163,101

Assets:

Cash Equivalents

^[1]

1,567

11,173

Commercial Paper [Member]

Total assets

^[1]

1,567

11,173

Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]

19,689

64,820

Certificates of Deposit [Member]

19,689

64,820

Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]

10,629

10,629

Corporate Bonds [Member]

Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]

94,609

46,490

Government Securities [Member]

94,609

46,490

Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]

33,466

15,819

33,466

15,819

Treasury Bonds [Member]

Treasury Bonds [Member] | Fair Value, Inputs, Level 2 [Member]

17,063

4,020

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

$ 17,063

$ 4,020

[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.

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair value, assets transfers from Level 1 to Level 2 measurement	$ 0	$ 0
Fair value, assets transfers from Level 2 to Level 1 measurement	0	0
Fair Value, assets transfers into (out of) Level 3 measurement	$ 0	$ 0

Investments - Schedule of Fair Value of Available-for-Sale Investments by Type of Security (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 175,603	$ 131,116
Gross Unrealized Gain	59	87
Gross Unrealized Loss	(206)	(54)
Fair Value	175,456	131,149
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	19,631	64,733
Gross Unrealized Gain	58	87
Fair Value	19,689	64,820
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	10,629
Fair Value	10,629
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	94,764	46,538
Gross Unrealized Loss	(155)	(48)
Fair Value	94,609	46,490
Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	33,513	15,823
Gross Unrealized Loss	(47)	(4)
Fair Value	33,466	15,819
Treasury Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	17,066	4,022
Gross Unrealized Gain	1
Gross Unrealized Loss	(4)	(2)
Fair Value	$ 17,063	$ 4,020

Investments - Additional Information (Detail)	12 Months Ended
Investments - Additional Information (Detail)	Dec. 31, 2016	Dec. 31, 2015
Investment [Line Items]
Maximum maturity days for cash equivalents	90 days
Corporate Bonds, Commercial Paper, Government Securities and Treasury Bonds [Member]
Investment [Line Items]
Remaining maturity period of investments		12 months

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 41,305	$ 8,762
Less: Accumulated depreciation and amortization	(5,180)	(1,011)
Property and equipment, net	36,125	7,751
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	10,711	4,370
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,335	408
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,010	285
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,807	1,856
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 442	$ 1,843

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 4,205	$ 728	$ 190

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Development and clinical manufacturing costs	$ 3,350	$ 1,436
Payroll and payroll-related costs	3,698	2,756
Professional fees	448	184
Facility and other	3,316	1,147
Total Accrued Expenses and Other Current Liabilities	$ 10,812	$ 5,523

Preferred Stock Warrant Liability - Additional Information (Detail) - USD ($)		1 Months Ended	12 Months Ended
	Aug. 17, 2015	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Jul. 01, 2015	Jun. 26, 2015	Dec. 31, 2013
Class of Stock [Line Items]
Fair value of warrant issuance			$ 0	$ 1,582,000	$ 0			$ 164,000
Loss from revaluation of preferred stock warrant liability			7,000	1,418,000
Common Stock [Member]
Class of Stock [Line Items]
Warrants exercise price per share	$ 1.78
Proceeds from exercise of warrant	$ 164,000
Common Stock [Member] \| Initial Public Offering ("IPO") [Member]
Class of Stock [Line Items]
Public offering price per share						$ 18.00	$ 18.00
Series A-2 Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Warrants issued to purchase of stock		92,127
Warrants exercise price per share		$ 1.78
Class of warrant or right, contractual term		10 years
Fair value of warrant issuance		$ 156,000	$ 17,260	$ 17,180

Preferred Stock Warrant Liability - Summary of Assumptions and Inputs Used in Determining Fair Value of Preferred Stock Warrant Liability Valued Using Black-Scholes Option-Pricing Model (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2013	Sep. 30, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk-free interest rate	2.40%	2.17%
Expected term (in years)	8 years 2 months 12 days	8 years 8 months 12 days
Expected volatility	91.20%	84.00%
Expected dividend yield	0.00%	0.00%
Fair value of Series A-2 convertible preferred stock	$ 0	$ 1,582,000	$ 0	$ 164,000
Series A-2 Convertible Preferred Stock [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value of Series A-2 convertible preferred stock	$ 17,260	$ 17,180			$ 156,000

Preferred Stock Warrant Liability - Summary of Rollforward of Fair Value of Preferred Stock Warrant Liability (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Beginning balance	$ 1,582	$ 164
Loss on revaluation	7	1,418
Reclassification to stockholders’ equity	(1,589)
Ending balance	$ 0	$ 1,582

Convertible Preferred Stock - Additional Information (Detail) - $ / shares	Dec. 31, 2016	Dec. 31, 2015	Jul. 01, 2015
Equity [Abstract]
Preferred stock, shares authorized	10,000,000	10,000,000	10,000,000
Preferred stock, par value	$ 0.001	$ 0.001	$ 0.001

Stockholders' Equity Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 02, 2015	Jun. 26, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Jul. 01, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized			200,000,000	38,000,000	200,000,000
Common stock, par value			$ 0.001	$ 0.001	$ 0.001
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued and sold	8,545,138		8,545,138	6,563
Net proceeds from issuance of common stock from IPO after deducting underwriting discounts and commissions	$ 139,267
Estimated stock offering expenses	$ 3,748
Conversion of redeemable convertible preferred stock into common stock		22,866,987	22,866,987
Initial Public Offering ("IPO") [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized						200,000,000
Common stock, par value						$ 0.001
Initial Public Offering ("IPO") [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offering price per share		$ 18.00				$ 18.00
Conversion of redeemable convertible preferred stock into common stock		22,866,987
Over-Allotment Option [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued and sold	1,114,583

Stockholders' Equity Common Stock - Common Stock Warrants - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended			13 Months Ended
	Jun. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 02, 2015	Aug. 17, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Research and development expense for fair value of the warrant		$ 81,989,000	$ 38,095,000	$ 10,718,000
Expected volatility			91.20%	84.00%
Risk-free interest rate			2.40%	2.17%
Expected term (in years)			8 years 2 months 12 days	8 years 8 months 12 days
Expected dividend yield			0.00%	0.00%
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants exercise price per share						$ 1.78
License Agreement Terms [Member] \| Mayo Foundation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants exercise price per share	$ 0.01
Research and development expense for fair value of the warrant	$ 317,000
Expected volatility	86.00%
Risk-free interest rate	2.30%
Expected term (in years)	7 years
Expected dividend yield	0.00%
Warrant exercised date	Apr. 29, 2015
License Agreement Terms [Member] \| Mayo Foundation [Member] \| Performance Warrant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants issued to purchase shares of common stock		284,090
Warrant expense					$ 0
License Agreement Terms [Member] \| Mayo Foundation [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants issued to purchase shares of common stock	454,545

Stockholders' Equity Common Stock - 2012 Stock Incentive plan - Additional Information (Detail) - 2012 Stock Incentive Plan [Member] - shares	12 Months Ended
	Dec. 31, 2016	Mar. 31, 2015	Dec. 31, 2014	May 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock incentive plan description	The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. The Company generally grants stock-based awards with service conditions only (“service-based” awards).
Shares available for future grant	0
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock that may be issued		4,309,653	3,608,029	3,561,836	1,261,836
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price per share of common stock expressed as a percentage	100.00%
Stock option granted vesting period	4 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option term	10 years
Stock option granted vesting period	4 years
Stock option expiration period	10 years

Stockholders' Equity Common Stock - 2015 Incentive Award Plan - Additional Information (Detail) - 2015 Incentive Award Plan [Member] - shares		12 Months Ended
	Jun. 16, 2015	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares initially reserved for issuance	2,200,000
Percentage of common stock shares outstanding	4.00%
Stock incentive plan description		The number of shares initially reserved for issuance under the 2015 Plan is the sum of (i) 2,200,000 shares of common stock and (ii) the number of shares subject to awards outstanding under the 2012 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company on or after the effective date of the 2015 Plan. In addition, the number of shares of common stock that may be issued under the 2015 Plan is subject to increase on the first day of each calendar year, beginning in 2016 and ending in 2025, equal to the lesser of (i) 4% of the number of shares of the Company’s common stock outstanding on the last day of the preceding applicable calendar year and (ii) an amount determined by the Company’s board of directors.
Shares available for future grant		1,352,907

Stockholders' Equity Common Stock - 2015 Employee Stock Purchase Plan - Additional Information (Detail) - 2015 Employee Stock Purchase Plan [Member] - shares		12 Months Ended
	Jun. 16, 2015	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate shares of common stock reserved for issuance	365,000
Shares issued under ESPP	400,000	0
Percentage of common stock shares outstanding	1.00%

Stockholders' Equity Common Stock - Summary of Estimated Fair Value of Employee Stock Options (Detail) - Stock Option Valuation [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.54%	1.80%	1.83%
Expected term (in years)	6 years	6 years	6 years
Expected volatility	84.20%	81.40%	83.50%
Expected dividend yield	0.00%	0.00%	0.00%

Stockholders' Equity Common Stock - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Number of shares, Beginning Balance	5,026,246
Number of Shares, Granted	1,695,125
Number of Shares, Exercised	(1,273,736)
Number of Shares, Forfeited	(378,502)
Number of shares, Ending Balance	5,069,133	5,026,246
Number of Shares, Options vested and expected to vest	5,069,133
Number of Shares, Options exercisable	1,686,284
Weighted Average Exercise Price, Beginning Balance	$ 8.01
Weighted Average Exercise Price, Granted	26.04
Weighted Average Exercise Price, Exercised	1.68
Weighted Average Exercise Price, Forfeited	24.93
Weighted Average Exercise Price, Ending Balance	14.36	$ 8.01
Weighted Average Exercise Price, Options vested and expected to vest	14.36
Weighted Average Exercise Price, Options exercisable	$ 8.05
Weighted Average Remaining Contractual Term, Outstanding	8 years 3 months 4 days	8 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	8 years 3 months 4 days
Weighted Average Remaining Contractual Term, Options exercisable	7 years 7 months 13 days
Aggregate Intrinsic Value, Outstanding	$ 16,736	$ 136,945
Aggregate Intrinsic Value, Options vested and expected to vest	16,736
Aggregate Intrinsic Value, Options exercisable	$ 9,048

Stockholders' Equity Common Stock - Stock Options - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options	$ 18.45	$ 14.56	$ 4.25
Intrinsic Value, Stock options exercised	$ 34,871	$ 4,125	$ 512
Stock based compensation expense for stock options	$ 16,857	$ 9,694	$ 2,068
Outstanding unvested service-based stock options	63,375	27,750
Stock Option [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance-Based stock options vested	60,000
Stock based compensation expense for stock options	$ 235
Grant date fair value of options	$ 3.92

Stockholders' Equity Common Stock - Summary of Restricted Stock Activity (Detail) - Restricted Stock Units [Member]	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted \| shares	115,500
Number of Shares, Unvested restricted stock units, Ending balance \| shares	115,500
Weighted Average Grant Date Fair Value, Granted \| $ / shares	$ 9.78
Weighted Average Grant Date Fair Value, Unvested restricted stock units, Ending balance \| $ / shares	$ 9.78

Stockholders' Equity Common Stock - Restricted Stock Units - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value, vested	$ 0	$ 1,508	$ 684

Stockholders' Equity Common Stock - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 16,857	$ 9,694	$ 2,068
Research and development expenses [Member] \| Stock Options and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	8,310	5,297	1,068
General and administrative expenses [Member] \| Stock Options and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 8,547	$ 4,397	$ 1,000

Stockholders' Equity Common Stock - Stock Based Compensation - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Equity [Abstract]
Unrecognized stock- based compensation cost	$ 35,405
Weighted average period over which unrecognized compensation cost is expected to be recognized	2 years 7 months 28 days

Collaboration Revenue - Additional Information (Detail) - USD ($)
$ in Thousands

1 Months Ended

3 Months Ended

12 Months Ended

Feb. 29, 2016

Jan. 31, 2016

Dec. 31, 2016

Sep. 30, 2016

Jun. 30, 2016

Mar. 31, 2016

Dec. 31, 2016

Period of performance identifiable deliverables

10 years

Phase 3 Clinical Trials [Member]

^[1]

$ 3,037

$ 13,015

$ 3,004

$ 2,710

$ 21,766

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Percentage of costs owned under clinical trial programs

67.00%

Nestlé Health Science [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront cash payment

$ 120,000

120,000

Development milestone payments

285,000

Regulatory payments

375,000

Sales based milestones

$ 1,125,000

Percentage of costs remaining under clinical trial programs

33.00%

Period of performance identifiable deliverables

10 years

Reimbursement of development services

580

Proceeds on achievement of development milestone

$ 10,000

10,000

Collaboration revenue associated with substantive milestones - related party

10,000

21,766

Deferred revenue

$ 108,800

[1]

Net Loss per Share - Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net loss	$ (25,274)	$ (18,688)	$ (27,913)	$ (19,704)	$ (19,634)	$ (14,620)	$ (12,555)	$ (7,971)	$ (91,579)	$ (54,780)	$ (16,709)
Accretion of convertible preferred stock to redemption value											(1,291)
Net loss attributable to common stockholders									$ (91,579)	$ (54,780)	$ (18,000)
Denominator:
Weighted average common shares outstanding, basic and diluted									39,846,928	23,532,400	6,748,037
Net loss per share attributable to common stockholders, basic and diluted	$ (0.63)	$ (0.46)	$ (0.70)	$ (0.50)	$ (0.50)	$ (0.38)	$ (1.45)	$ (1.15)	$ (2.30)	$ (2.33)	$ (2.67)

Net Loss per Share - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	5,184,633	5,026,246	25,940,702
Convertible Preferred Stock (as Converted to 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			21,478,098
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	5,069,133	5,026,246	3,579,342
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	115,500
Unvested Restricted 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			52,500
Warrants for the Purchase of Convertible Preferred 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			92,127
Warrants for the Purchase of 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			738,635

Commitments and Contingencies - Additional Information (Detail)			12 Months Ended
	Nov. 11, 2015 USD ($) ft²	Apr. 02, 2015	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2016 USD ($)
Other Commitments [Line Items]
Operating lease agreement expiration date			Jun. 30, 2016
Operating lease termination write off of deferred rent benefit			$ 136,000
Outstanding security deposit						$ 119,000
Lease incentive obligation			10,730,000	$ 586,000
Indemnification Agreement [Member]
Other Commitments [Line Items]
Indemnification obligations accrued			$ 0	0
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			$ 12,080,000
Amortized of lease incentive obligation			429,000
Office and Laboratory Space [Member]
Other Commitments [Line Items]
Operating lease agreement expiration date		Apr. 30, 2020
Rental expense related to office and laboratory space			$ 3,826,000	$ 1,246,000	$ 543,000

Commitments and Contingencies - Summary Of Future Minimum Lease Payments For Operating Leases (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2017	$ 5,978
2018	6,158
2019	6,342
2020	6,120
2021	6,222
2022 and thereafter	11,529
Total	$ 42,349

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Line Items]
Income tax benefit	$ 0	$ 0	$ 0
Massachusetts Life Sciences Center [Member]
Income Tax Disclosure [Line Items]
Tax incentives awarded	900,000
Tax incentives reversed	$ 900,000
Tax incentive program period	5 years
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 47,165,000
Net operating loss carry forwards, expiration year, start	2031
Research and development tax credit carryforwards, expiration year, start	2031
Federal [Member] \| Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Research and development tax credit carryforwards	$ 13,500,000
Federal [Member] \| Orphan Drug Credit Carryforwards [Member]
Income Tax Disclosure [Line Items]
Research and development tax credit carryforwards	8,473,000
State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 46,296,000
Net operating loss carry forwards, expiration year, start	2031
Research and development tax credit carryforwards, expiration year, start	2028
State [Member] \| Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Research and development tax credit carryforwards	$ 2,260,000
Stock Based Compensation Tax Benefit \| Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	20,211,000
Stock Based Compensation Tax Benefit \| State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 20,211,000

Income Taxes - Schedule of Reconciliation of U.S Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(34.00%)	(34.00%)	(34.00%)
Research and development tax credits	(8.80%)	(5.70%)	(3.80%)
State taxes, net of federal benefit	(5.80%)	(5.30%)	(5.30%)
Stock-based compensation	(6.30%)	4.10%	2.30%
Revaluation of preferred stock warrant liability			3.30%
Other	0.10%	0.30%	0.20%
Change in deferred tax asset valuation allowance	54.80%	40.60%	37.30%
Effective income tax rate	0.00%	0.00%	0.00%

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Net operating loss carryforwards	$ 18,481	$ 25,293
Research and development tax credit carryforwards	14,991	4,180
Capitalized organization costs	483	527
Stock-based compensation expense	5,624	1,897
Charitable Contributions	6	5
Deferred Revenue	42,742
Accrued expenses	5,560	977
Capitalized research and development expenses	115	126
Total deferred tax assets	88,002	33,005
Deferred tax liabilities:
Depreciation and amortization	(5,008)	(228)
Total deferred tax liabilities	(5,008)	(228)
Valuation allowance	$ (82,994)	(32,777)	$ (10,522)	$ (4,294)
Net deferred tax assets		$ 0

Income Taxes - Summary of Changes In Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation Allowance [Abstract]
Valuation allowance at beginning of year	$ (32,777)	$ (10,522)	$ (4,294)
Increases recorded to income tax provision	(50,217)	(22,255)	(6,228)
Valuation allowance as of end of year	$ (82,994)	$ (32,777)	$ (10,522)

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2016

Sep. 30, 2016

Jun. 30, 2016

Mar. 31, 2016

Dec. 31, 2015

Sep. 30, 2015

Jun. 30, 2015

Mar. 31, 2015

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Quarterly Financial Data [Abstract]

Net loss per share attributable to common stockholders, basic and diluted

^[1]

$ 3,037

$ 13,015

$ 3,004

$ 2,710

$ 21,766

Total operating expenses

28,725

32,110

31,144

22,626

$ 19,788

$ 14,561

$ 12,340

$ 8,167

114,605

$ 54,856

$ 15,082

Loss from operations

(25,688)

(19,095)

(28,140)

(19,916)

(19,788)

(14,561)

(12,340)

(8,167)

(92,839)

(54,856)

(15,082)

Net loss

$ (25,274)

$ (18,688)

$ (27,913)

$ (19,704)

$ (19,634)

$ (14,620)

$ (12,555)

$ (7,971)

$ (91,579)

$ (54,780)

$ (16,709)

$ (0.63)

$ (0.46)

$ (0.70)

$ (0.50)

$ (0.38)

$ (1.45)

$ (1.15)

$ (2.30)

$ (2.33)

$ (2.67)

[1]

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Parenthetical) (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Feb. 29, 2016	Jan. 31, 2016	Sep. 30, 2016	Dec. 31, 2016
Quarterly Financial Information [Line Items]
Performance period for revenue recognized		10 years
Nestlé Health Science [Member]
Quarterly Financial Information [Line Items]
Upfront cash payment	$ 120,000	$ 120,000		$ 120,000
Proceeds on achievement of development milestone			$ 10,000	10,000
Collaboration revenue recognized for milestone - related party				$ 10,000
Performance period for revenue recognized		10 years

Related Party Transactions - Additional Information (Detail) - USD ($)

3 Months Ended

12 Months Ended

Dec. 31, 2016

Sep. 30, 2016

Jun. 30, 2016

Mar. 31, 2016

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Flagship Pioneering [Member] | Services Agreement [Member]

^[1]

$ 3,037,000

$ 13,015,000

$ 3,004,000

$ 2,710,000

$ 21,766,000

Payments under agreements with related party

17,000

$ 502,000

$ 454,000

Due to related party

$ 0

Nestlé Health Science [Member]

Payments under agreements with related party

Due to related party

306,000