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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2015	Aug. 07, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2
Trading Symbol	MCRB
Entity Registrant Name	Seres Therapeutics, Inc.
Entity Central Index Key	0001609809
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		38,963,640

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 36,338	$ 114,185
Investments	55,438	0
Prepaid expenses and other current assets	2,288	58
Total current assets	94,064	114,243
Property and equipment, net	3,319	1,264
Restricted cash	139	139
Deferred offering costs	3,748	1,684
Deferred financing costs	11	15
Total assets	101,281	117,345
Current liabilities:
Accounts payable	1,688	2,166
Accrued expenses and other current liabilities	2,753	1,737
Notes payable, current portion	1,200	1,200
Total current liabilities	5,641	5,103
Notes payable, net of discount	727	1,304
Preferred stock warrant liability		1,582
Total liabilities	6,368	7,989
Commitments and contingencies
Stockholders' equity (deficit):
Common stock, $0.001 par value; 65,000,000 and 38,000,000 shares authorized at June 30, 2015 and December 31, 2014, respectively; 30,416,627 and 6,890,250 shares issued and outstanding at June 30, 2015 and December 31, 2014 , respectively	31	7
Additional paid-in capital	143,217	1,104
Accumulated other comprehensive income	23
Accumulated deficit	(48,358)	(27,832)
Total stockholders' equity (deficit)	94,913	(26,721)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 101,281	117,345
Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member]
Current liabilities:
Convertible preferred stock (Series A, A-2, B, C, D and D-1), value		$ 136,077

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	65,000,000	38,000,000
Common stock, shares issued	30,416,627	6,890,250
Common stock, shares outstanding	30,416,627	6,890,250
Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member]
Convertible preferred stock, par value	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized	24,348,003	24,348,003
Convertible preferred stock, shares issued	0	22,866,987
Convertible preferred stock, shares outstanding	0	22,866,987
Convertible preferred stock, liquidation preference	$ 0	$ 139,992

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development expenses	8,784	2,160	14,345	3,192
General and administrative expenses	3,556	458	6,162	1,098
Total operating expenses	12,340	2,618	20,507	4,290
Loss from operations	(12,340)	(2,618)	(20,507)	(4,290)
Other income (expense):
Interest income (expense), net	5	(56)	(12)	(93)
Revaluation of preferred stock warrant liability	(220)	(3)	(7)	17
Total other income (expense), net	(215)	(59)	(19)	(76)
Net loss	(12,555)	(2,677)	(20,526)	(4,366)
Accretion of convertible preferred stock to redemption value		(325)		(558)
Net loss attributable to common stockholders	$ (12,555)	$ (3,002)	$ (20,526)	$ (4,924)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.45)	$ (0.45)	$ (2.64)	$ (0.73)
Weighted average common shares outstanding, basic and diluted	8,640,218	6,725,625	7,777,679	6,706,392
Other comprehensive income:
Unrealized gain (loss) on investments, net of tax of $0	$ (8)		$ 23
Total other comprehensive income	(8)		23
Comprehensive loss	$ (12,563)	$ (2,677)	$ (20,503)	$ (4,366)

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Unrealized gain on investment, tax	$ 0	$ 0	$ 0	$ 0

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - 6 months ended Jun. 30, 2015 - USD ($) $ in Thousands	Total	Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member]	Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member] Series D Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Stockholders' equity (deficit), value, beginning balance at Dec. 31, 2014	$ (26,721)				$ 1,104	$ (27,832)
Stockholders' equity (deficit), shares, beginning balance at Dec. 31, 2014	6,890,250			6,890,250
Stockholders' equity (deficit), par value, beginning balance at Dec. 31, 2014	$ 0.001			$ 7
Convertible preferred stock, value, beginning balance at Dec. 31, 2014		$ 136,077
Convertible preferred stock, shares, beginning balance at Dec. 31, 2014		22,866,987
Issuance costs of convertible preferred stock			$ (24)
Issuance of common stock upon exercise of stock options, value	$ 90				90
Issuance of common stock upon exercise of stock options, shares	204,845			204,845
Issuance of common stock upon exercise of common stock warrant, value	$ 5				4
Issuance of common stock upon exercise of common stock warrant, shares				454,545
Issuance of common stock upon exercise of common stock warrant, par value				$ 1
Stock-based compensation expense	4,400				4,400
Reclassification of preferred stock warrant liability	1,589				1,589
Conversion of convertible preferred stock listing of the Company's common stock on the NASDAQ , value	136,053	$ (136,053)			136,030
Conversion of convertible preferred stock upon listing of the Company's common stock on the NASDAQ , shares		(22,866,987)		22,866,987
Conversion of convertible preferred stock upon listing of the Company's common stock on the NASDAQ , par value				$ 23
Unrealized gain on investments	23						$ 23
Net loss	(20,526)					(20,526)
Stockholders' equity (deficit), value, ending balance at Jun. 30, 2015	$ 94,913				$ 143,217	$ (48,358)	$ 23
Stockholders' equity (deficit), shares, ending balance at Jun. 30, 2015	30,416,627			30,416,627
Stockholders' equity (deficit), par value, ending balance at Jun. 30, 2015	$ 0.001			$ 31
Convertible preferred stock, value, ending balance at Jun. 30, 2015		$ 0
Convertible preferred stock, shares, ending balance at Jun. 30, 2015		0

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net loss	$ (20,526)	$ (4,366)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,400	97
Depreciation and amortization expense	212	66
(Gain) loss from revaluation of preferred stock warrant liability	7	(17)
Licensing fees paid in common stock warrant		317
Non-cash interest expense	141	35
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,230)	6
Accounts payable	(141)	124
Accrued expenses and other current liabilities	141	239
Net cash used in operating activities	(17,996)	(3,499)
Cash flows from investing activities:
Purchases of property and equipment	(1,649)	(312)
Purchases of investments	(64,250)
Maturities of investments	8,725
Changes in restricted cash		(102)
Net cash used in investing activities	(57,174)	(414)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	(24)	10,558
Proceeds from issuance of notes payable		1,500
Proceeds from exercise of stock options and common stock warrants	95
Repayment of notes payable	(600)
Payments of initial public offering costs	(2,148)
Net cash (used in) provided by financing activities	(2,677)	12,058
Net (decrease) increase in cash and cash equivalents	(77,847)	8,145
Cash and cash equivalents at beginning of period	114,185	1,654
Cash and cash equivalents at end of period	36,338	9,799
Supplemental disclosure of cash flow information:
Cash paid for interest	75	51
Supplemental disclosure of non-cash investing and financing activities:
Conversion of convertible preferred stock into common stock upon listing of the Company's common stock on the NASDAQ	136,053
Accretion of convertible preferred stock to redemption value		558
Deferred offering costs included in accounts payable and accrued expenses	780
Property and equipment purchases included in accounts payable and accrued expenses	$ 718	$ 4

Nature of the Business and Basis of Presentation

6 Months Ended

Jun. 30, 2015

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 intended to prevent further recurrences of Clostridium difficile infection (“CDI”), a debilitating infection of the colon, and, if approved by the FDA, could be a first-in-field drug. Using its microbiome therapeutics platform, the Company is developing additional product candidates, including SER-262 to prevent an initial recurrence of primary CDI and other product candidates to treat inflammatory bowel disease, including ulcerative colitis, and enteric pathogens, such as antibiotic-resistant bacteria. The Company is also conducting research on metabolic diseases, such as early-stage, non-insulin dependent diabetes; other inflammatory diseases, such as Crohn’s disease; and infections related to antibiotic use, cancer chemotherapy and immune suppression.

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.

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 $139,304 after deducting underwriting discounts and commissions and estimated 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.

Unaudited Interim Financial Information

The accompanying unaudited consolidated financial statements as of June 30, 2015 and for the three months and six months ended June 30, 2015 and 2014 have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2014 included in the Company’s final prospectus filed under the Securities Act of 1933, as amended, with the SEC pursuant to Rule 424(b)(4) on June 26, 2015.

The unaudited interim financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position as of June 30, 2015 and consolidated results of operations for the three and six months ended June 30, 2015 and 2014 and its cash flows for the six months ended June 30, 2015 and 2014. Such adjustments are of a normal and recurring nature. The results of operations for the three and six months ended June 30, 2015 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2015.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2015

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 stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

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 commercial paper 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 $139 as of June 30, 2015 and December 31, 2014 in a separate restricted bank account as a security deposit for the lease of the Company’s facilities and as collateral for the Company’s credit card program with Comerica Bank. 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, investments and preferred stock warrant liability are carried at fair value, determined according to the fair value hierarchy described above. 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. The carrying value of the Company’s outstanding debt as of June 30, 2015 and December 31, 2014 approximates fair value based on the variable interest rate for the borrowings outstanding as well as the short duration of the term of the note. The fair value of the outstanding debt was estimated using a discounted cash flow analysis based on current market interest rates for debt issuances with similar remaining years to maturity, adjusted for credit risk, which represents a Level 3 measurement.

The following table presents information about the Company’s assets and liabilities as of June 30, 2015 and December 31, 2014 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 June 30, 2015 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash Equivalents	$	—	$	16,750	$	—	$	16,750
Investments:
Corporate Bonds	$	—	$	16,939	$	—	$	16,939
Commercial Paper		—		35,499		—		35,499
Government Secrurities		—		3,000		—		3,000

	$	—	$	72,188	$	—	$	72,188


	Fair Value Measurements as of December 31, 2014 Using:
	Level 1		Level 2		Level 3		Total
Liabilities:
Liability for preferred stock warrant	$	—	$	—	$	1,582	$	1,582

	$	—	$	—	$	1,582	$	1,582

As of June 30, 2015, the Company’s cash equivalents, which were invested in money market funds, corporate bonds and commercial paper with original maturities of less than 90 days from the date of purchase, were valued based on Level 2 inputs. The fair values of the Company’s investments, which consisted of corporate bonds, commercial paper and government securities as of June 30, 2015, were determined using Level 2 inputs. During the three and six months ended June 30, 2015 and 2014, there were no transfers between Level 1, Level 2 and Level 3.

The liability for the preferred stock warrant in the amount of $1,582 in the table above as of December 31, 2014 is comprised of the values of a warrant for the purchase of Series A-2 convertible preferred stock and is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. There were no other assets or liabilities measured at a fair value on a recurring basis at June 30, 2015 or December 31, 2014.

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 June 30, 2015 and December 31, 2014 the Company had recorded $3,748 and $1,684, respectively, of deferred offering costs in contemplation of the IPO. 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, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock options and restricted stock awards with only service-based vesting conditions and records the expense for these awards using the straight-line method.

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 re-measured 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 compensation expense for only the portion of awards that are expected to vest. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre-vesting forfeitures for service-based awards. The impact of a forfeiture rate adjustment will be recognized in full in the period of adjustment, and if the actual forfeiture rate is materially different from the Company’s estimate, the Company may be required to record adjustments to stock-based compensation expense in future periods.

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.

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 the 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.

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.

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. No revenue has been generated since inception, and 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. For the three and six months ended June 30, 2015, other comprehensive income (loss) consisted of changes in unrealized gains (losses) from available-for-sale investments. There was no difference between net loss and comprehensive loss for the three and six months ended June 30, 2014.

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 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 entitled the holders of such shares to participate in dividends but did 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.

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


	Three and Six Months Ended June 30,
	2015		2014
Stock options to purchase common stock		4,809,621		1,261,836
Unvested restricted common stock		1,250		103,750
Warrants for the purchase of convertible preferred stock		—		92,127
Warrants for the purchase of common stock		92,127		738,635
Convertible preferred stock (as converted to common stock)		—		15,309,548

		4,902,998		17,505,896

Recently Issued Accounting Standards

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 July 2015, the FASB decided to delay the effective date of the new revenue standard by one year. The new standard will be effective for us on January 1, 2018. The FASB also agreed to allow entities to choose to adopt the standard as of the original effective date. We are currently evaluating the method of adoption and the potential impact that Topic 606 may have on our financial position and results of operations.

In April 2015, the FASB issued ASU 2015-03, Simplifying the Presentation of Debt Issuance Costs. The amendments in this update require that debt issuance costs be presented in the balance sheet as a direct deduction from the carrying amount of the debt liability. The new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. Early adoption is permitted. The Company is currently evaluating the potential impact of the adoption of this standard, but believes its adoption will not have a material impact on its financial statements.

Investments

6 Months Ended

Jun. 30, 2015

Investments, Debt and Equity Securities [Abstract]

Investments

3.	Investments

As of June 30, 2015, the fair value of available-for-sale investments by type of security was as follows:


	June 30, 2015
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Corporate bonds	$	16,941	$	—	$	(2	)	$	16,939
Commercial paper		35,473		26		—			35,499
Government securities		3,001		—		(1	)		3,000

	$	55,415	$	26	$	(3	)	$	55,438

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. The Company did not hold any investments as of December 31, 2014.

As of June 30, 2015, the Company’s corporate bonds, commercial paper and government securities 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

6 Months Ended

Jun. 30, 2015

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

4.	Property and Equipment, Net

Property and equipment, net consisted of the following:


	June 30, 2015			December 31, 2014
Laboratory equipment	$	1,898		$	1,260
Computer equipment		115			115
Furniture and office equipment		173			58
Leasehold improvements		114			114
Construction in progress		1,514			—

		3,814			1,547
Less: Accumulated depreciation and amortization		(495	)		(283	)

	$	3,319		$	1,264

Construction in progress at June 30, 2015 was comprised primarily of leasehold improvements and laboratory equipment purchased in connection with the build-out of laboratory space in one of our Cambridge, Massachusetts facilities.

Depreciation and amortization expense was $119, $212, $36 and $66 for the three and six months ended June 30, 2015 and 2014, respectively.

Accrued Expenses and Other Current Liabilities

6 Months Ended

Jun. 30, 2015

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

5.	Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:


	June 30, 2015		December 31, 2014
Development and manufacturing costs	$	558	$	598
Payroll and payroll-related costs		906		547
Professional fees		772		314
Facility and other		517		278

	$	2,753	$	1,737

Notes Payable

6 Months Ended

Jun. 30, 2015

Debt Disclosure [Abstract]

Notes Payable

6.	Notes Payable

On September 9, 2013, the Company entered into a loan and security agreement with Comerica Bank (“Comerica”), as amended on December 22, 2014, which provided for borrowings of up to $3,000 through August 2014. On September 9, 2013, the Company received $1,000 from borrowings under the agreement, and from March to August 2014, the Company received $2,000 from additional borrowings under the agreement. Through December 31, 2014, the Company borrowed the full $3,000 available under the loan and security agreement and had made $1,000 of scheduled principal repayments. During the six months ended June 30, 2015, the Company made $600 of scheduled principal repayments. Borrowings under the loan and security agreement are collateralized by substantially all of the Company’s assets, except for its intellectual property.

In accordance with the terms of the loan and security agreement, the Company is obligated to make monthly, interest-only payments on any term loans funded under the agreement until August 1, 2014. Thereafter, the Company is obligated to pay 30 consecutive, equal monthly installments of principal and interest from September 1, 2014 through February 1, 2017, the maturity date. Term loans under the loan and security agreement bear interest at an annual rate equal to 3.0% plus the greater of (1) the bank’s prime rate and (2) the LIBOR rate plus 2.5%. As of June 30, 2015, the greater rate was 6.25%. In addition, a final payment of $60 is due upon the earlier of the maturity date, acceleration of the term loans or prepayment of all or part of the term loans. That amount is being recorded as additional interest expense over the term of the loan and security agreement, using the effective interest method.

Accretion of the debt discount recorded as additional interest expense was $12, $23, $16 and $33 for the three and six months ended June 30, 2015 and 2014, respectively. As of June 30, 2015 and December 31, 2014, the unamortized debt discount was $73 and $96, respectively. The debt discount, which also reflected $26 of fees paid to the lender, is being accreted to the carrying value of the debt, using the effective interest method.

There are no financial covenants associated with the loan and security agreement; however, there are negative covenants restricting the Company’s activities, including limitations on dispositions, mergers or acquisitions, encumbering or granting a security interest in its intellectual property, incurring indebtedness or liens, paying dividends, making certain investments and engaging in certain other business transactions. The obligations under the loan and security agreement are subject to acceleration upon the occurrence of specified events of default, including a material adverse change in the Company’s business, operations or financial or other condition.

As of June 30, 2015, annual principal repayment requirements under the loan and security agreement were $1,200 during each of the years ending December 31, 2015 and 2016, and $200 during the year ending December 31, 2017.

Preferred Stock Warrant Liability

6 Months Ended

Jun. 30, 2015

Text Block [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 its loan and security agreement. The warrant was immediately exercisable at an exercise price of $1.78 per share and has 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 $220, $7 and $3 for the three and six months ended June 30, 2015 and the three months ended June 30, 2014, respectively, and a gain of $17 for the six months ended June 30, 2014 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:


	Six Months Ended June 30,
	2015			2014
Risk-free interest rate		2.40	%		2.56	%
Expected term (in years)		8.2			9.2
Expected volatility		91.2	%		86.0	%
Expected dividend yield		0	%		0	%
Fair value of Series A-2 convertible preferred stock	$	17.26		$	1.59

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


Balance as of December 31, 2014	$	1,582
Loss on revaluation		7
Reclassification to stockholders’ equity		(1,589	)

Balance as of June 30, 2015	$	—

Convertible Preferred Stock

6 Months Ended

Jun. 30, 2015

Equity [Abstract]

Convertible Preferred Stock

8.	Convertible Preferred Stock

As of June 30, 2015, the Company’s Amended and Restated Certificate of Incorporation, as further amended, authorized the Company to issue 24,348,003 shares of preferred 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 10,000,000 shares of preferred stock, $0.001 par value per share.

All outstanding shares of the Company’s convertible preferred stock automatically converted into 22,866,987 shares of the Company’s common stock upon the listing of the Company’s common stock on the NASDAQ on June 26, 2015

Stockholders' Equity

6 Months Ended

Jun. 30, 2015

Equity [Abstract]

Stockholders' Equity

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 $139,304 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 June 30, 2015 and December 31, 2014, the Company’s Amended and Restated Certificate of Incorporation, as further amended, authorized the Company to issue 65,000,000 and 38,000,000 shares, respectively, 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 Warrant

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 or net share settlement, the Company determined that this warrant qualifies 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, which was $18.00 as of June 30, 2015 and December 31, 2014. 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 related. 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 June 30, 2015.

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

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.

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.

Stock Options

The following table summarizes the Company’s stock option activity since December 31, 2014:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2014		3,579,342		$	1.38		9.21	$	59,498
Granted		1,486,624			17.44
Exercised		(204,845	)		0.44
Forfeited		(51,500	)		1.62

Outstanding as of June 30, 2015		4,809,621		$	6.38		9.13	$	168,916

Options exercisable as of June 30, 2015		1,072,686		$	0.56		8.48	$	43,917

Options vested and expected to vest as of June 30, 2015		4,809,621		$	6.38		9.13	$	168,916

The weighted average grant-date fair value of stock options granted during the three and six months ended June 30, 2015 was $13.40 and $12.18 per share.

During the six months ended June 30, 2015, the Company granted performance-based stock options to employees for the purchase of an aggregate of 30,000 shares of common stock with a grant date fair value of $12.89 per share. These stock options are exercisable only upon achievement of specified performance targets. As of June 30, 2015, none of these options were exercisable because none of the specified performance targets had been achieved. Because achievement of the specified performance targets was not deemed probable as of June 30, 2015, the Company did not record any expense for these stock options from the dates of issuance through June 30, 2015.

As of June 30, 2015, there were outstanding unvested service-based stock options held by non-employees for the purchase of 56,563 shares of common stock.

Restricted Common Stock

The Company has granted restricted common stock with time-based vesting conditions. Unvested shares of restricted common stock may not be sold or transferred by the holder. These restrictions lapse according to the time-based vesting conditions of each award. The table below summarizes the Company’s restricted stock activity since December 31, 2014:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted common stock as of December 31, 2014		52,500		$	0.001
Vested		(51,250	)	$	0.001

Unvested restricted common stock as of June 30, 2015		1,250		$	0.001

Stock-based Compensation Expense

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


	Three Months Ended June 30,				Six Months Ended June 30,
	2015		2014		2015		2014
Research and development expenses	$	1,891	$	40	$	2,514	$	72
General and administrative expenses		1,182		12		1,886		25

	$	3,073	$	52	$	4,400	$	97

Income Taxes

6 Months Ended

Jun. 30, 2015

Income Tax Disclosure [Abstract]

Income Taxes

10.

Income Taxes

The Company did not provide for any income taxes in any of the three or six month periods ended June 30, 2015 or 2014.

The Company has evaluated the positive and negative evidence bearing upon the realizability of its U.S. net deferred tax assets. As required by the provisions of ASC 740, Income Taxes, management has determined that it is more-likely-than-not that the Company will not utilize the benefits of federal and state U.S. net deferred tax assets for financial reporting purposes. Accordingly, the net deferred tax assets are subject to a valuation allowance at June 30, 2015 and December 31, 2014.

As of June 30, 2015 and December 31, 2014, the Company had no accrued interest or tax penalties recorded. The Company files income tax returns in the U.S. and various state jurisdictions. The federal and state income tax returns are generally subject to tax examinations for the tax years ended 2011 through 2014. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated my still be adjusted upon examination by the Internal Revenue Service or state tax authorizes to the extent it is utilized in a future period. There are no currently ongoing or pending examinations in any jurisdictions.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2015

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

11.

Commitments and Contingencies

Leases

The Company leases office and laboratory space under an operating lease agreement. The lease expires in January 2018 with no extension periods. The Company has a right of expansion over the term as additional space becomes available but not an obligation. On February 13, 2015, the Company entered into a sublease for office space with a term expiring in February 2016. On April 1, 2015, the Company entered into a lease for additional office and laboratory space with a term expiring in April 2020.

During the three and six months ended June 30, 2015 and 2014, the Company recognized $354, $540, $183 and $225, respectively, of rental expense related to office and laboratory space.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors 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, 2014 or June 30, 2015.

Related Party Transactions

6 Months Ended

Jun. 30, 2015

Related Party Transactions

12.

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, 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 $131, $249 , $115 and $261 during the three and six months ended June 30, 2015 and 2014, respectively. As of June 30, 2015, there were no amounts due to Flagship Ventures Management, Inc. related to the services agreement.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References + Details

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

Use of Estimates

Cash Equivalents

Restricted Cash

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.

Concentration of Credit Risk and of Significant Suppliers

Concentration of Credit Risk and of Significant Suppliers

Fair Value Measurements

Fair Value Measurements

•

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

•


	Fair Value Measurements as of June 30, 2015 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash Equivalents	$	—	$	16,750	$	—	$	16,750
Investments:
Corporate Bonds	$	—	$	16,939	$	—	$	16,939
Commercial Paper		—		35,499		—		35,499
Government Securities		—		3,000		—		3,000

	$	—	$	72,188	$	—	$	72,188


	Fair Value Measurements as of December 31, 2014 Using:
	Level 1		Level 2		Level 3		Total
Liabilities:
Liability for preferred stock warrant	$	—	$	—	$	1,582	$	1,582

	$	—	$	—	$	1,582	$	1,582

Deferred Offering Costs

Deferred Offering Costs

Property and Equipment

Property and Equipment

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets

Research and Development Costs

Research and Development Costs

Research Contract Costs and Accruals

Research Contract Costs and Accruals

Patent Costs

Patent Costs

Accounting for Stock-Based Compensation

Accounting for Stock-Based Compensation

Income Taxes

Income Taxes

Warrant to Purchase Convertible Preferred Stock

Warrant to Purchase Convertible Preferred Stock

Segment Data

Segment Data

Comprehensive Loss

Comprehensive Loss

Net Loss per Share

Net Loss per Share


	Three and Six Months Ended June 30,
	2015		2014
Stock options to purchase common stock		4,809,621		1,261,836
Unvested restricted common stock		1,250		103,750
Warrants for the purchase of convertible preferred stock		—		92,127
Warrants for the purchase of common stock		92,127		738,635
Convertible preferred stock (as converted to common stock)		—		15,309,548

		4,902,998		17,505,896

Recently Issued Accounting Standards

Recently Issued Accounting Standards

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

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


	Fair Value Measurements as of June 30, 2015 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash Equivalents	$	—	$	16,750	$	—	$	16,750
Investments:
Corporate Bonds	$	—	$	16,939	$	—	$	16,939
Commercial Paper		—		35,499		—		35,499
Government Secrurities		—		3,000		—		3,000

	$	—	$	72,188	$	—	$	72,188


	Fair Value Measurements as of December 31, 2014 Using:
	Level 1		Level 2		Level 3		Total
Liabilities:
Liability for preferred stock warrant	$	—	$	—	$	1,582	$	1,582

	$	—	$	—	$	1,582	$	1,582

Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share


	Three and Six Months Ended June 30,
	2015		2014
Stock options to purchase common stock		4,809,621		1,261,836
Unvested restricted common stock		1,250		103,750
Warrants for the purchase of convertible preferred stock		—		92,127
Warrants for the purchase of common stock		92,127		738,635
Convertible preferred stock (as converted to common stock)		—		15,309,548

		4,902,998		17,505,896

Investments (Tables)

6 Months Ended

Jun. 30, 2015

Investments, Debt and Equity Securities [Abstract]

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

As of June 30, 2015, the fair value of available-for-sale investments by type of security was as follows:


	June 30, 2015
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Corporate bonds	$	16,941	$	—	$	(2	)	$	16,939
Commercial paper		35,473		26		—			35,499
Government securities		3,001		—		(1	)		3,000

	$	55,415	$	26	$	(3	)	$	55,438

- 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)

6 Months Ended

Jun. 30, 2015

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consisted of the following:


	June 30, 2015			December 31, 2014
Laboratory equipment	$	1,898		$	1,260
Computer equipment		115			115
Furniture and office equipment		173			58
Leasehold improvements		114			114
Construction in progress		1,514			—

		3,814			1,547
Less: Accumulated depreciation and amortization		(495	)		(283	)

	$	3,319		$	1,264

Accrued Expenses and Other Current Liabilities (Tables)

6 Months Ended

Jun. 30, 2015

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:


	June 30, 2015		December 31, 2014
Development and manufacturing costs	$	558	$	598
Payroll and payroll-related costs		906		547
Professional fees		772		314
Facility and other		517		278

	$	2,753	$	1,737

Preferred Stock Warrant Liability (Tables)

6 Months Ended

Jun. 30, 2015

Text Block [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:


	Six Months Ended June 30,
	2015			2014
Risk-free interest rate		2.40	%		2.56	%
Expected term (in years)		8.2			9.2
Expected volatility		91.2	%		86.0	%
Expected dividend yield		0	%		0	%
Fair value of Series A-2 convertible preferred stock	$	17.26		$	1.59

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:


Balance as of December 31, 2014	$	1,582
Loss on revaluation		7
Reclassification to stockholders’ equity		(1,589	)

Balance as of June 30, 2015	$	—

Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2015

Equity [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since December 31, 2014:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2014		3,579,342		$	1.38		9.21	$	59,498
Granted		1,486,624			17.44
Exercised		(204,845	)		0.44
Forfeited		(51,500	)		1.62

Outstanding as of June 30, 2015		4,809,621		$	6.38		9.13	$	168,916

Options exercisable as of June 30, 2015		1,072,686		$	0.56		8.48	$	43,917

Options vested and expected to vest as of June 30, 2015		4,809,621		$	6.38		9.13	$	168,916

Summary of Restricted Stock Activity

The table below summarizes the Company’s restricted stock activity since December 31, 2014:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted common stock as of December 31, 2014		52,500		$	0.001
Vested		(51,250	)	$	0.001

Unvested restricted common stock as of June 30, 2015		1,250		$	0.001

Summary of Stock Based Compensation Expense


	Three Months Ended June 30,				Six Months Ended June 30,
	2015		2014		2015		2014
Research and development expenses	$	1,891	$	40	$	2,514	$	72
General and administrative expenses		1,182		12		1,886		25

	$	3,073	$	52	$	4,400	$	97

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended
	Jul. 01, 2015	Jun. 26, 2015	Jun. 30, 2015
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporated year			Oct. 31, 2010
Entity incorporated state name			State of Delaware
Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Conversion of redeemable convertible preferred stock into common stock		22,866,987	22,866,987
Subsequent Event [Member] \| Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from issuance of common stock from IPO after deducting underwriting discounts and commissions	$ 139,304
Initial Public Offering ("IPO") [Member] \| Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Public offering price per share		$ 18.00
Conversion of redeemable convertible preferred stock into common stock		22,866,987
Initial Public Offering ("IPO") [Member] \| Subsequent Event [Member] \| Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock issued and sold	8,545,138
Public offering price per share	$ 18.00
Underwriters Option to Purchase Additional Shares [Member] \| Subsequent Event [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 ($)		3 Months Ended		6 Months Ended
	Jul. 01, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 26, 2015	Dec. 31, 2014
Accounting Policies [Line Items]
Maximum maturity days for cash equivalents				90 days
Restricted cash		$ 139,000		$ 139,000			$ 139,000
Fair value, assets transfers from Level 1 to Level 2 measurement		0	$ 0	0	$ 0
Fair value, assets transfers from Level 2 to Level 1 measurement		0	0	0	0
Fair Value, assets transfers into (out of) Level 3 measurement		0	0	0	0
Deferred offering costs		3,748,000		3,748,000			1,684,000
Impairment losses on long lived assets				$ 0
Minimum percentage of likelihood of tax benefit being realized upon settlement				50.00%
Revenue		0	$ 0	$ 0	$ 0
Subsequent Event [Member]
Accounting Policies [Line Items]
Reclassification of deferred offering costs to additional paid in capital	$ 3,748,000
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
Initial Public Offering ("IPO") [Member]
Accounting Policies [Line Items]
Deferred offering costs		$ 3,748,000		$ 3,748,000			1,684,000
Initial Public Offering ("IPO") [Member] \| Common Stock [Member]
Accounting Policies [Line Items]
Public offering price per share						$ 18.00
Initial Public Offering ("IPO") [Member] \| Common Stock [Member] \| Subsequent Event [Member]
Accounting Policies [Line Items]
Public offering price per share	$ 18.00
Fair Value, Inputs, Level 3 [Member]
Accounting Policies [Line Items]
Liability for preferred stock warrant							$ 1,582,000

Summary of Significant Accounting Policies - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	$ 16,750
Investments
Total assets	72,188
Liabilities:
Liability for preferred stock warrant		$ 1,582
Total liabilities		1,582
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member]
Investments
Investments	16,939
Fair Value, Measurements, Recurring [Member] \| Commercial Paper [Member]
Investments
Investments	35,499
Fair Value, Measurements, Recurring [Member] \| Government Securities [Member]
Investments
Investments	3,000
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	16,750
Investments
Total assets	72,188
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member]
Investments
Investments	16,939
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Commercial Paper [Member]
Investments
Investments	35,499
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Government Securities [Member]
Investments
Investments	$ 3,000
Fair Value, Inputs, Level 3 [Member]
Liabilities:
Liability for preferred stock warrant		1,582
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Liabilities:
Liability for preferred stock warrant		1,582
Total liabilities		$ 1,582

Summary of Significant Accounting Policies - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	4,902,998	17,505,896	4,902,998	17,505,896
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	4,809,621	1,261,836	4,809,621	1,261,836
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	1,250	103,750	1,250	103,750
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		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	92,127	738,635	92,127	738,635
Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share		15,309,548		15,309,548

Investments - Schedule of Fair Value of Available-for-Sale Investments by Type of Security (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 55,415
Gross Unrealized Gain	26
Gross Unrealized Loss	(3)
Fair Value	55,438
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	16,941
Gross Unrealized Loss	(2)
Fair Value	16,939
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	35,473
Gross Unrealized Gain	26
Fair Value	35,499
Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,001
Gross Unrealized Loss	(1)
Fair Value	$ 3,000

Investments - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Original maturity period of investments	90 days
Investments	$ 55,438	$ 0
Corporate Bonds, Commercial Paper and Government Securities [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	Jun. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3,814	$ 1,547
Less: Accumulated depreciation and amortization	(495)	(283)
Property and equipment, net	3,319	1,264
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,898	1,260
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	115	115
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	173	58
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	114	$ 114
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,514

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 119	$ 36	$ 212	$ 66

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Development and manufacturing costs	$ 558	$ 598
Payroll and payroll-related costs	906	547
Professional fees	772	314
Facility and other	517	278
Total Accrued Expenses and Other Current Liabilities	$ 2,753	$ 1,737

Notes Payable - Additional Information (Detail) - Comerica [Member]		3 Months Ended		6 Months Ended			12 Months Ended
	Sep. 09, 2013 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) Installments	Aug. 31, 2014 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Additional interest expense		$ 12,000	$ 23,000	$ 16,000		$ 33,000
Unamortized debt discount		73,000		73,000			$ 96,000
Debt fee amount		26,000		26,000
Annual principal repayment, 2015		1,200,000		1,200,000
Annual principal repayment, 2016		1,200,000		1,200,000
Annual principal repayment, 2017		$ 200,000		200,000
Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Borrowings amount	$ 3,000,000
Amount received from borrowings	$ 1,000,000				$ 2,000,000		3,000,000
Principal repayments amount				$ 600,000			$ 1,000,000
Number of installments \| Installments				30
Interest rate description				Term loans under the loan and security agreement bear interest at an annual rate equal to 3.0% plus the greater of (1) the bank's prime rate and (2) the LIBOR rate plus 2.5%. As of June 30, 2015, the greater rate was 6.25%.
Interest rate percentage		3.00%		3.00%
Interest rate percentage				6.25%
Debt maturity date start				Sep. 01, 2014
Debt maturity date end				Feb. 01, 2017
Final payment of term loan				$ 60,000
Loan and Security Agreement [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Interest rate percentage				2.50%

Preferred Stock Warrant Liability - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 26, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Fair value of warrant issuance		$ 17,260	$ 1,590	$ 17,260	$ 1,590		$ 1,582,000
Gain (loss) recorded to adjust change in fair value of preferred stock warrant		(220,000)	(3,000)	(7,000)	17,000
Preferred Stock [Member]
Class of Stock [Line Items]
Gain (loss) recorded to adjust change in fair value of preferred stock warrant		$ (220,000)	$ (3,000)	$ (7,000)	$ 17,000
Common Stock [Member] \| Initial Public Offering ("IPO") [Member]
Class of Stock [Line Items]
Public offering price per share						$ 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

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 ($)	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Fair Value Inputs, Quantitative Information [Abstract]
Risk-free interest rate	2.40%	2.56%
Expected term (in years)	8 years 2 months 12 days	9 years 2 months 12 days
Expected volatility	91.20%	86.00%
Expected dividend yield	0.00%	0.00%
Fair value of Series A-2 convertible preferred stock	$ 17,260	$ 1,590	$ 1,582,000

Preferred Stock Warrant Liability - Summary of Rollforward of Fair Value of Preferred Stock Warrant Liability (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value Inputs, Quantitative Information [Abstract]
Balance as of December 31, 2014			$ 1,582,000
Loss on revaluation	$ 220,000	$ 3,000	7,000	$ (17,000)
Reclassification to stockholders' equity			(1,589,000)
Balance as of June 30, 2015	$ 17,260	$ 1,590	$ 17,260	$ 1,590

Convertible Preferred Stock - Additional Information (Detail) - $ / shares		6 Months Ended
	Jun. 26, 2015	Jun. 30, 2015	Jul. 01, 2015	Dec. 31, 2014
Common Stock [Member]
Class of Stock [Line Items]
Conversion of redeemable convertible preferred stock into common stock	22,866,987	22,866,987
Initial Public Offering ("IPO") [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Conversion of redeemable convertible preferred stock into common stock	22,866,987
Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member]
Class of Stock [Line Items]
Convertible preferred stock, shares authorized		24,348,003		24,348,003
Convertible preferred stock, par value		$ 0.001		$ 0.001
Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Convertible preferred stock, shares authorized			10,000,000
Convertible preferred stock, par value			$ 0.001

Stockholders' Equity - Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended
	Jul. 01, 2015	Jun. 26, 2015	Jun. 30, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized			65,000,000	38,000,000
Common stock, par value			$ 0.001	$ 0.001
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion of redeemable convertible preferred stock into common stock		22,866,987	22,866,987
Common stock, par value			$ 31	$ 7
Common Stock [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net proceeds from issuance of common stock from IPO after deducting underwriting discounts and commissions	$ 139,304
Estimated stock offering expenses	$ 3,748
Initial Public Offering ("IPO") [Member] \| Subsequent Event [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
Conversion of redeemable convertible preferred stock into common stock		22,866,987
Initial Public Offering ("IPO") [Member] \| Common Stock [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued and sold	8,545,138
Public offering price per share	$ 18.00
Over-Allotment Option [Member] \| Common Stock [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued and sold	1,114,583
Amended and Restated Certificate of Incorporation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized			65,000,000	38,000,000
Common stock, par value			$ 0.001	$ 0.001

Stockholders' Equity - Common Stock Warrant - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Research and development expense for fair value of the warrant		$ 8,784,000	$ 2,160,000	$ 14,345,000	$ 3,192,000
Expected volatility				91.20%	86.00%
Risk-free interest rate				2.40%	2.56%
Expected term (in years)				8 years 2 months 12 days	9 years 2 months 12 days
Expected dividend yield				0.00%	0.00%
Mayo Foundation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants exercise price per share	$ 0.01		$ 0.01		$ 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
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		454,545		454,545
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		284,090
Warrants exercise price per share		$ 18.00		$ 18.00		$ 18.00
Warrant expense				$ 0

Stockholders' Equity - 2012 Stock Incentive plan - Additional Information (Detail) - 2012 Stock Incentive Plan [Member]	6 Months Ended
	Jun. 30, 2015
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). Stock options granted generally vest over four years and expire after ten years, although options have been granted with vesting terms less than four years.
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 - 2015 Incentive Award Plan - Additional Information (Detail) - 2015 Incentive Award Plan [Member] - shares		6 Months Ended
	Jun. 16, 2015	Jun. 30, 2015
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.

Stockholders' Equity - 2015 Employee Stock Purchase Plan - Additional Information (Detail) - 2015 Employee Stock Purchase Plan [Member]	Jun. 16, 2015 shares
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
Percentage of common stock shares outstanding	1.00%

Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Equity [Abstract]
Number of shares, Beginning Balance	3,579,342
Number of shares, Granted	1,486,624
Number of shares, Exercised	(204,845)
Number of shares, Forfeited	(51,500)
Number of shares, Ending Balance	4,809,621	3,579,342
Number of shares, Options exercisable	1,072,686
Number of shares, Options vested and expected to vest	4,809,621
Weighted Average Exercise Price, Beginning Balance	$ 1.38
Weighted Average Exercise Price, Granted	17.44
Weighted Average Exercise Price, Exercised	0.44
Weighted Average Exercise Price, Forfeited	1.62
Weighted Average Exercise Price, Ending Balance	6.38	$ 1.38
Weighted Average Exercise Price, Options exercisable	0.56
Weighted Average Exercise Price, Options vested and expected to vest	$ 6.38
Weighted Average Remaining Contractual Term, Outstanding	9 years 1 month 17 days	9 years 2 months 16 days
Weighted Average Remaining Contractual Term, Options exercisable	8 years 5 months 23 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	9 years 1 month 17 days
Aggregate Intrinsic Value, Beginning Balance	$ 59,498
Aggregate Intrinsic Value, Ending Balance	168,916	$ 59,498
Aggregate Intrinsic Value, Options exercisable	43,917
Aggregate Intrinsic Value, Options vested and expected to vest	$ 168,916

Stockholders' Equity - Stock Options - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of stock options	$ 13.40		$ 12.18
Expense for stock options	$ 3,073,000	$ 52,000	$ 4,400,000	$ 97,000
Outstanding unvested service-based stock options	56,563		56,563
Stock Option [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance-Based stock options granted			30,000
Grant date fair value of options			$ 12.89
Stock option exercisable	0		0
Expense for stock options			$ 0

Stockholders' Equity - Summary of Restricted Stock Activity (Detail) - Restricted Common Stock [Member]	6 Months Ended
	Jun. 30, 2015 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested restricted common stock, Beginning balance \| shares	52,500
Number of Shares, Vested \| shares	(51,250)
Number of Shares, Unvested restricted common stock, Ending balance \| shares	1,250
Weighted Average Grant Date Fair Value, Unvested restricted common stock, Beginning balance \| $ / shares	$ 0.001
Weighted Average Grant Date Fair Value, Vested \| $ / shares	0.001
Weighted Average Grant Date Fair Value, Unvested restricted common stock, Ending balance \| $ / shares	$ 0.001

Stockholders' Equity - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 3,073	$ 52	$ 4,400	$ 97
Research and Development Expense [Member] \| Stock Options and Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,891	40	2,514	72
General and Administrative Expense [Member] \| Stock Options and Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,182	$ 12	$ 1,886	$ 25

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0	$ 0	$ 0
Accrued interest or tax penalties	$ 0		$ 0		$ 0

Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Other Commitments [Line Items]
Operating lease agreement expiration date			Jan. 31, 2018
Office and Laboratory Space [Member]
Other Commitments [Line Items]
Rental expense related to office and laboratory space	$ 354,000	$ 183,000	$ 540,000	$ 225,000
Indemnification Agreement [Member]
Other Commitments [Line Items]
Indemnification obligations accrued	$ 0		$ 0		$ 0

Related Party Transactions - Additional Information (Detail) - Flagship Ventures Management, Inc. [Member] - Services Agreement [Member] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Related Party Transaction [Line Items]
Payments under agreements with related party	$ 131,000	$ 115,000	$ 249,000	$ 261,000
Due to related party	$ 0		$ 0