Global Blood Therapeutics (GBT) 10-Q 12 May 16 2016 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2016	May. 06, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	Global Blood Therapeutics, Inc.
Entity Central Index Key	1,629,137
Document Type	10-Q
Document Fiscal Period Focus	Q1
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Amendment Flag	false
Entity Common Stock, Shares Outstanding		30,531,425

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 133,984	$ 148,502
Prepaid expenses	1,907	1,222
Other assets, current	647	1,096
Total current assets	136,538	150,820
Property and equipment, net	2,293	2,114
Restricted cash	140	140
Total assets	138,971	153,074
Current liabilities:
Accounts payable	4,295	3,361
Accrued liabilities	4,738	4,400
Accrued compensation	1,715	2,242
Other liabilities, current	747	720
Total current liabilities	11,495	10,723
Other liabilities, noncurrent	1,354	1,556
Total liabilities	$ 12,849	$ 12,279
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized as of March 31, 2016 and December 31, 2015	$ 0	$ 0
Common stock, $0.001 par value, 150,000,000 shares authorized as of March 31, 2016 (unaudited) and December 31, 2015, respectively; 29,536,449 and 29,359,800 shares issued and outstanding as of March 31, 2016 (unaudited) and December 31, 2015, respectively	30	29
Additional paid-in capital	241,157	239,231
Accumulated deficit	(115,065)	(98,465)
Total stockholders’ equity	126,122	140,795
Total liabilities and stockholders’ equity	$ 138,971	$ 153,074

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2016	Dec. 31, 2015
Stockholders’ equity (deficit):
Preferred stock, par value in usd per share	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Common stock, par value in usd per share	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	94,000,000
Common stock, shares issued	29,536,449	29,359,800
Common stock, shares outstanding	29,536,449	29,359,800

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating expenses:
Research and development	$ 12,415	$ 6,069
General and administrative	4,302	1,298
Related party expenses	0	53
Total operating expenses	16,717	7,420
Loss from operations	(16,717)	(7,420)
Interest income	117	3
Net loss	(16,600)	(7,417)
Comprehensive loss	(16,600)	(7,417)
Net loss attributable to common stockholders	$ (16,600)	$ (8,657)
Net loss per share attributable to common stockholders, basic and diluted (usd per share)	$ (0.56)	$ (4.22)
Weighted-average number of shares used in computing net loss per share attributable to common stockholders, basic and diluted (shares)	29,441,404	2,052,874

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (16,600)	$ (7,417)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	242	183
Loss on disposal of fixed assets	0	18
Stock-based compensation	1,267	322
Changes in operating assets and liabilities:
Prepaid expenses	(685)	378
Other assets, current	(3)	(362)
Accounts payable	867	334
Payable due to related party	0	39
Accrued liabilities	814	754
Accrued compensation	(527)	(305)
Other liabilities	(9)	(5)
Net cash used in operating activities	(14,634)	(6,061)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(378)	(169)
Net cash used in investing activities	(378)	(169)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments of deferred offering costs	0	(67)
Proceeds from issuance of restricted stock awards	0	45
Repurchase of unvested restricted stock awards	0	(17)
Proceeds from issuance of common stock in settlement of employee stock purchase plan and exercise of stock options	494	0
Net cash provided by (used in) financing activities	494	(39)
Net decrease in cash and cash equivalents	(14,518)	(6,269)
Cash and cash equivalents at beginning of period	148,502	52,069
Cash and cash equivalents at end of period	133,984	45,800
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Accretion of Series A and Series B redeemable convertible preferred stock	0	1,240
Accrued purchase of property and equipment	43	356
Accrued offering costs	$ 0	$ 620

Organization and Basis of Prese

Organization and Basis of Presentation	3 Months Ended
	Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation Global Blood Therapeutics Inc. (the “Company”, “we”, “us”, and “our”) was incorporated in Delaware in February 2011 and commenced operations in May 2012 . We are a clinical-stage biopharmaceutical company dedicated to discovering, developing and commercializing novel therapeutics to treat grievous blood-based disorders with significant unmet needs. Our primary activities have been establishing our facilities, recruiting personnel, conducting development of our product candidates, including clinical trials, and raising capital. Our principal operations are based in South San Francisco, California, and we operate in one segment. Need for Additional Capital In the course of our development activities, we have sustained operating losses and we expect such losses to continue over the next several years. Our ultimate success depends on the outcome of our research and development activities. Since inception through March 31, 2016 , we have incurred cumulative net losses of $115.1 million . We expect to incur additional losses in the future to conduct product research and development and we recognize the need to raise additional capital to fully implement our business plan. We intend to raise such capital through the issuance of additional equity, and potentially through borrowings, and strategic alliances with partner companies. However, if such financing is not available at adequate levels, we will need to reevaluate our operating plans. We believe that our existing cash and cash equivalents will be sufficient to fund our cash requirements through mid-2017.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Preparation The accompanying unaudited interim condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2015 has been derived from audited financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. These unaudited interim condensed financial statements have been prepared on the same basis as our annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair presentation of our financial information. The results of operations for the three months ended March 31, 2016 are not necessarily indicative of the results to be expected for the year ending December 31, 2016 or for any other interim period or for any other future year. The accompanying interim unaudited condensed financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2015 included in our Annual Report on Form 10-K, filed with the SEC on March 29, 2016. Use of Estimates The preparation of the accompanying unaudited interim condensed financial statements in accordance with U.S. GAAP requires us 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 condensed financial statements, and the reported amounts of costs and expenses during the reporting period. We base our estimates and assumptions on historical experience when available and on various factors that we believe to be reasonable under the circumstances. We evaluate our estimates and assumptions on an ongoing basis. Our actual results could differ from these estimates under different assumptions or conditions. Cash and Cash Equivalents We consider all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents, which consist primarily of amounts invested in money market accounts, are stated at fair value. Accruals of Research and Development Costs We record accruals for estimated costs of research, preclinical, nonclinical and clinical studies and manufacturing development. These costs are a significant component of our research and development expenses. A substantial portion of our ongoing research and development activities are conducted by third-party service providers, including contract research organizations. We accrue the costs incurred under our agreements with these third parties based on actual work completed in accordance with agreements established with these third parties. We determine the actual costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fee to be paid for such services. We make significant judgments and estimates in determining the accrual balance in each reporting period. As actual costs become known, we adjust our accruals. We have not experienced any material deviations between accrued clinical trial expenses and actual clinical trial expenses. However, actual services performed, number of subjects enrolled, and the rate of subject enrollment may vary from our estimates, resulting in adjustments to clinical trial expense in future periods. Changes in these estimates that result in material changes to our accruals could materially affect our results of operations. Concentration of Credit Risk Financial instruments that potentially subject us to a concentration of credit risk consist of cash and cash equivalents. Our cash and cash equivalents are held primarily in one large financial institution in the United States. We believe that this financial institution is financially sound, and accordingly, minimal credit risk exists with respect to this financial institution. Fair Value Measurement The carrying amounts of certain financial instruments, including cash and cash equivalents, restricted cash, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. Research and Development Costs Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to other nonemployees and entities that conduct certain research and development activities on our behalf. Amounts incurred in connection with license agreements are also included in research and development expense. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and then expensed as the related goods are delivered or the services are performed. Stock-based Compensation We measure and recognize stock-based compensation expense, including employee and non-employee equity awards, based on fair value at the grant date. We use the Black-Scholes option-pricing model to calculate fair value. Stock-based compensation expense recognized in the statements of operations is based on options ultimately expected to vest, taking into consideration estimated forfeitures. Stock-based compensation expense is revised in subsequent periods, if necessary, if actual forfeitures differ from these estimates. When estimating forfeitures, we consider historic voluntary termination behaviors as well as trends of actual option forfeitures. For options granted to non-employees, we revalue the unearned portion of the stock-based compensation and the resulting change in fair value is recognized in the statements of operations over the period the related services are rendered. Net Loss per Share Attributable to Common Stockholders Net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. The net loss attributable to common stockholders is calculated by adjusting our net loss for the accretion and dividends on redeemable convertible preferred stock. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since the effects of potentially dilutive securities are antidilutive given our net loss. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board ("FASB") or other standards setting bodies that are adopted by us as of the specified effective date. Unless otherwise discussed, we believe that the impact of recently issued standards that are not yet effective will not have a material impact on our financial statements upon adoption. In February 2016, the FASB issued Accounting Standards Update, or ASU No. 2016-02, Leases. The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases. The standard is effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted. We are currently in the process of evaluating the impact the adoption of this new standard will have on our financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-09. The new standard simplifies the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The standard is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. We are currently in the process of evaluating the impact the adoption of this new standard will have on our financial position or results of operations and have not elected to early adopt the amendments.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis (at least annually). Financial instruments include cash and cash equivalents, restricted cash, accounts payable and accrued liabilities that approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 – Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 – Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 – Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Financial assets subject to fair value measurements on a recurring basis and the level of inputs used in such measurements are as follows (in thousands): March 31, 2016 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 134,124 $ — $ — $ 134,124 Total financial assets $ 134,124 $ — $ — $ 134,124 December 31, 2015 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 148,642 $ — $ — $ 148,642 Total financial assets $ 148,642 $ — $ — $ 148,642 Our financial instruments consist of Level 1 assets. Where quoted prices for identical assets are available in an active market, securities are classified as Level 1. Level 1 assets consist of highly liquid money market funds, which as of March 31, 2016 and December 31, 2015 includes $140,000 of funds that are collateral for our facility lease that are included within restricted cash. There were no unrealized gains and losses in our investments in these money market funds.

Balance Sheet Components

Balance Sheet Components	3 Months Ended
	Mar. 31, 2016
Balance Sheet Components [Abstract]
Balance Sheet Components	Balance Sheet Components Property and Equipment Property and equipment consists of the following: (in thousands) March 31, 2016 December 31, 2015 Laboratory equipment $ 3,275 $ 3,151 Computer equipment 930 596 Leasehold improvements 348 340 Construction-in-progress 84 129 Total property and equipment 4,637 4,216 Less: accumulated depreciation and amortization (2,344 ) (2,102 ) Property and equipment, net $ 2,293 $ 2,114 Accrued liabilities Accrued liabilities consist of the following: (in thousands) March 31, 2016 December 31, 2015 Accrued clinical and manufacturing expenses $ 4,089 $ 4,025 Accrued professional and consulting services 646 287 Other 3 88 Total accrued liabilities $ 4,738 $ 4,400 Other liabilities, noncurrent Other noncurrent liabilities consist of the following: (in thousands) March 31, 2016 December 31, 2015 Restricted shares subject to repurchase, noncurrent $ 1,278 $ 1,470 Deferred rent, noncurrent 76 86 Total other liabilities, noncurrent $ 1,354 $ 1,556

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2016
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Common Stock We have reserved the following shares of common stock for issuance as follows: March 31, 2016 Restricted shares subject to future vesting 992,176 Options issued and outstanding 2,487,374 Options available for future grants 2,379,284 Employee stock purchase plan 112,100 Total common stock reserved for issuance 5,970,934 Restricted Stock In May 2012, we issued 1,345,709 shares of restricted common stock to founders at $0.0035 per share, all of which are fully vested as of March 31, 2016 . Under the related stock purchase agreements, we have the right to repurchase the common stock which right lapses according to individual vesting schedules. In addition, we have issued restricted stock awards to employees under our 2012 Stock Option and Grant Plan (the "2012 Plan"). Under the related stock purchase agreements, we have the right to repurchase the common stock at the lower of fair market value and the stockholders’ original purchase price which right lapses according to individual vesting schedules. In order to vest, the holders are required to provide continued service to us. Upon vesting, the appropriate amounts are transferred from liabilities to additional paid in capital. If the employment or other service relationship of the holder of any unvested restricted common stock is terminated for any reason, we have the right to repurchase the unvested shares at the lower of fair market value or the stockholder’s original purchase price. As such, the shares subject to future vesting are not deemed outstanding for accounting purposes until the shares vest. Restricted shares subject to repurchase and related liability were as follows: (in thousands except share data) March 31, 2016 December 31, 2015 Restricted shares subject to repurchase: Shares issued to founders — 6,250 Shares issued pursuant to the 2012 Stock Option and Grant Plan 992,176 1,091,038 Total restricted shares subject to repurchase 992,176 1,097,288 Liability pertaining to restricted shares subject to repurchase Other liabilities, current 703 677 Other liabilities, noncurrent 1,278 1,470 Total liabilities pertaining to shares subject to repurchase $ 1,981 $ 2,147

Stock-based Awards

Stock-based Awards	3 Months Ended
	Mar. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based Awards	Stock-based Awards Equity Incentive Plans In July 2015 , we adopted the 2015 Stock Option and Incentive Plan (the “2015 Plan”). Under the 2015 Plan, 1,430,000 shares of our common stock were initially reserved for the issuance of stock options, restricted stock, and other equity-based awards to employees, non-employee directors, and consultants under terms and provisions established by the Board of Directors and approved by our stockholders. The 2015 Plan also provides for automatic annual increases in the number of shares reserved for future issuance. As of March 31, 2016 , there were 2,379,284 shares available for us to grant under the 2015 Plan. In 2012, we adopted the 2012 Plan under which the Board of Directors was authorized to grant incentive stock options to employees, including officers and members of the Board of Directors who are also employees of ours, and non-statutory stock options (options that do not qualify as incentive options) and/or our restricted stock and other equity-based awards to employees, officers, directors, or consultants of ours. Upon adoption of the 2015 Plan, no new awards or grants are permitted under the 2012 Plan. Employee Stock Purchase Plan In July 2015, we adopted the 2015 Employee Stock Purchase Plan (the “2015 ESPP”). Under the 2015 ESPP, 50,000 shares of our common stock have been initially reserved for employee purchases of our common stock under terms and provisions established by the Board of Directors and approved by our stockholders. The 2015 ESPP also provides for automatic annual increases in the number of shares reserved for future issuance. Stock Option Awards The following summarizes option activity under the 2015 Plan and the 2012 Plan: Number of Options Weighted- Average Exercise Price Weighted- Average remaining contractual term (years) Aggregate Intrinsic Value (in thousands) Balance Outstanding, December 31, 2015 2,058,787 $ 8.71 9.0 Options granted 606,425 $ 15.09 Options exercised (42,266 ) $ 0.53 Options canceled (135,572 ) $ 22.10 Balance Outstanding, March 31, 2016 2,487,374 $ 9.67 9.0 $ 21,586 Exercisable, March 31, 2016 482,249 $ 3.96 8.2 $ 6,131 Vested and expected to vest, March 31, 2016 2,334,962 $ 9.50 9.0 $ 20,555 Stock Options Granted to Employees with Service-Based Vesting Conditions Valuation Assumptions The fair values of stock options granted to employees were calculated using the following assumptions: Three Months Ended 2016 2015 Expected term (in years) 5.8-6.1 6.0-6.1 Volatility 79.4%-81.0% 75.9%-77.0% Risk-free interest rate 1.3%-1.9% 1.5%-1.7% Dividend yield — — Performance-Contingent Awards On April 9, 2015 , our Board of Directors granted a total of 326,424 performance-contingent awards to members of our senior management team. Of the total performance-contingent awards granted, 227,139 were performance-contingent options and 99,285 were performance-contingent shares of restricted common stock. The exercise price of each performance-contingent option and the purchase price for the performance-contingent restricted shares is $3.40 per share, which the Board of Directors determined was the fair market value on the grant date. These awards have dual triggers of vesting based upon the successful achievement of four corporate operating milestones within specified timelines, as well as a requirement for continued employment. When a performance goal is deemed to be probable of achievement, time-based vesting and recognition of stock-based compensation expense commences. In the event any of the corporate operating milestones are not achieved by the specified timelines, such vesting tranche will terminate and no longer be exercisable with respect to that portion of the shares. During the first quarter ended March 31, 2016 , the Compensation Committee of our Board of Directors determined that the achievement of one of the corporate operating milestones was met; accordingly, shares associated with this milestone vested and, as a result, $100,000 of compensation cost was recognized for the performance-contingent awards. Market-Condition Award On April 9, 2015 , our Board of Directors granted a market-condition award to our Chief Executive Officer of 99,285 shares of restricted common stock. The market-condition award does not vest until our market capitalization (determined based on the number of shares of common stock outstanding multiplied by the closing market price for our common stock as reported on NASDAQ) exceeds at least $2.0 billion for 20 consecutive trading days on or before the date twenty-four ( 24 ) months after the closing of our initial public offering, or IPO. The fair value of the market-condition award of $0.70 was determined on the grant date utilizing a lattice model that was prepared by a third party valuation firm with an expected term of 2.4 years . In August 2015, we began to recognize compensation costs for this award concurrent with the closing of our IPO. Stock-Based Compensation Expense Total stock-based compensation recognized by function was as follows (in thousands): Three Months Ended 2016 2015 Research and development $ 545 $ 265 General and administrative 722 57 Total stock-based compensation expense $ 1,267 $ 322 Total stock-based compensation recognized for employees and non-employees was as follows (in thousands): Three Months Ended 2016 2015 Employee options and restricted stock awards $ 1,200 $ 293 Non-employee options 67 29 Total stock-based compensation expense $ 1,267 $ 322 Unrecognized Stock-Based Compensation Expense and Weighted-Average Remaining Amortization Period As of March 31, 2016 the unrecognized stock-based compensation cost, net of expected forfeitures, and the estimated weighted-average amortization period, using the straight-line attribution method, was as follows (in thousands, except amortization period): Unrecognized Compensation Cost Weighted-average remaining amortization period (years) Options $ 14,022 2.9 Restricted stock awards 828 2.3 ESPP 215 0.2 Total unrecognized stock-based compensation expense $ 15,065

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders	Net Loss per Share Attributable to Common Stockholders The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders during the three months ended March 31, 2016 and 2015 , respectively (in thousands, except share and per share data): Three Months Ended 2016 2015 Numerator: Net loss $ (16,600 ) $ (7,417 ) Accretion and dividends on redeemable convertible preferred stock — (1,240 ) Net loss attributable to common stockholders $ (16,600 ) $ (8,657 ) Denominator: Weighted average common shares outstanding 29,441,404 2,052,874 Net loss per share attributable to common stockholders, basic and diluted $ (0.56 ) $ (4.22 ) Since we were in a loss position for all periods presented, diluted net loss per share attributable to common stockholders is the same as basic net loss per share for all periods as the inclusion of all potential common shares outstanding would have been anti-dilutive. Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Three Months Ended 2016 2015 Redeemable convertible preferred stock as if converted — 19,746,614 Options to purchase common stock 2,487,374 1,190,051 Restricted stock subject to future vesting 992,176 985,338 2015 ESPP 58,921 — Total 3,538,471 21,922,003

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2016
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Our largest investors include investment funds controlled by Third Rock Ventures, LLC (“TRV”) and two members of our Board of Directors are also partners in TRV. Management and advisory fee expense incurred with TRV was zero for the three months ended March 31, 2016 and $53,000 for the three months ended March 31, 2015 .

Summary of Significant Accoun14

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Basis of Preparation	Basis of Preparation The accompanying unaudited interim condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2015 has been derived from audited financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. These unaudited interim condensed financial statements have been prepared on the same basis as our annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair presentation of our financial information. The results of operations for the three months ended March 31, 2016 are not necessarily indicative of the results to be expected for the year ending December 31, 2016 or for any other interim period or for any other future year. The accompanying interim unaudited condensed financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2015 included in our Annual Report on Form 10-K, filed with the SEC on March 29, 2016.
Use of Estimates	Use of Estimates The preparation of the accompanying unaudited interim condensed financial statements in accordance with U.S. GAAP requires us 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 condensed financial statements, and the reported amounts of costs and expenses during the reporting period. We base our estimates and assumptions on historical experience when available and on various factors that we believe to be reasonable under the circumstances. We evaluate our estimates and assumptions on an ongoing basis. Our actual results could differ from these estimates under different assumptions or conditions.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents, which consist primarily of amounts invested in money market accounts, are stated at fair value.
Accruals of Research and Development Costs	Accruals of Research and Development Costs We record accruals for estimated costs of research, preclinical, nonclinical and clinical studies and manufacturing development. These costs are a significant component of our research and development expenses. A substantial portion of our ongoing research and development activities are conducted by third-party service providers, including contract research organizations. We accrue the costs incurred under our agreements with these third parties based on actual work completed in accordance with agreements established with these third parties. We determine the actual costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fee to be paid for such services. We make significant judgments and estimates in determining the accrual balance in each reporting period. As actual costs become known, we adjust our accruals. We have not experienced any material deviations between accrued clinical trial expenses and actual clinical trial expenses. However, actual services performed, number of subjects enrolled, and the rate of subject enrollment may vary from our estimates, resulting in adjustments to clinical trial expense in future periods. Changes in these estimates that result in material changes to our accruals could materially affect our results of operations.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject us to a concentration of credit risk consist of cash and cash equivalents. Our cash and cash equivalents are held primarily in one large financial institution in the United States. We believe that this financial institution is financially sound, and accordingly, minimal credit risk exists with respect to this financial institution.
Fair Value Measurement	Fair Value Measurement The carrying amounts of certain financial instruments, including cash and cash equivalents, restricted cash, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to other nonemployees and entities that conduct certain research and development activities on our behalf. Amounts incurred in connection with license agreements are also included in research and development expense. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and then expensed as the related goods are delivered or the services are performed.
Stock-based Compensation	Stock-based Compensation We measure and recognize stock-based compensation expense, including employee and non-employee equity awards, based on fair value at the grant date. We use the Black-Scholes option-pricing model to calculate fair value. Stock-based compensation expense recognized in the statements of operations is based on options ultimately expected to vest, taking into consideration estimated forfeitures. Stock-based compensation expense is revised in subsequent periods, if necessary, if actual forfeitures differ from these estimates. When estimating forfeitures, we consider historic voluntary termination behaviors as well as trends of actual option forfeitures. For options granted to non-employees, we revalue the unearned portion of the stock-based compensation and the resulting change in fair value is recognized in the statements of operations over the period the related services are rendered.
Net Loss per Share Attributable to Common Stockholders	Net Loss per Share Attributable to Common Stockholders Net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. The net loss attributable to common stockholders is calculated by adjusting our net loss for the accretion and dividends on redeemable convertible preferred stock. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since the effects of potentially dilutive securities are antidilutive given our net loss.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board ("FASB") or other standards setting bodies that are adopted by us as of the specified effective date. Unless otherwise discussed, we believe that the impact of recently issued standards that are not yet effective will not have a material impact on our financial statements upon adoption. In February 2016, the FASB issued Accounting Standards Update, or ASU No. 2016-02, Leases. The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases. The standard is effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted. We are currently in the process of evaluating the impact the adoption of this new standard will have on our financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-09. The new standard simplifies the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The standard is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. We are currently in the process of evaluating the impact the adoption of this new standard will have on our financial position or results of operations and have not elected to early adopt the amendments.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis	Financial assets subject to fair value measurements on a recurring basis and the level of inputs used in such measurements are as follows (in thousands): March 31, 2016 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 134,124 $ — $ — $ 134,124 Total financial assets $ 134,124 $ — $ — $ 134,124 December 31, 2015 Level 1 Level 2 Level 3 Total Financial Assets: Money market funds $ 148,642 $ — $ — $ 148,642 Total financial assets $ 148,642 $ — $ — $ 148,642

Balance Sheet Components (Table

Balance Sheet Components (Tables)	3 Months Ended
	Mar. 31, 2016
Balance Sheet Components [Abstract]
Property and Equipment	Property and Equipment Property and equipment consists of the following: (in thousands) March 31, 2016 December 31, 2015 Laboratory equipment $ 3,275 $ 3,151 Computer equipment 930 596 Leasehold improvements 348 340 Construction-in-progress 84 129 Total property and equipment 4,637 4,216 Less: accumulated depreciation and amortization (2,344 ) (2,102 ) Property and equipment, net $ 2,293 $ 2,114
Accrued Expenses	Accrued liabilities consist of the following: (in thousands) March 31, 2016 December 31, 2015 Accrued clinical and manufacturing expenses $ 4,089 $ 4,025 Accrued professional and consulting services 646 287 Other 3 88 Total accrued liabilities $ 4,738 $ 4,400
Other Liabilities, Noncurrent	Other noncurrent liabilities consist of the following: (in thousands) March 31, 2016 December 31, 2015 Restricted shares subject to repurchase, noncurrent $ 1,278 $ 1,470 Deferred rent, noncurrent 76 86 Total other liabilities, noncurrent $ 1,354 $ 1,556

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2016
Equity [Abstract]
Schedule of common stock reserved for issuance	e have reserved the following shares of common stock for issuance as follows: March 31, 2016 Restricted shares subject to future vesting 992,176 Options issued and outstanding 2,487,374 Options available for future grants 2,379,284 Employee stock purchase plan 112,100 Total common stock reserved for issuance 5,970,934
Schedule of restricted shares subject to repurchase	Restricted shares subject to repurchase and related liability were as follows: (in thousands except share data) March 31, 2016 December 31, 2015 Restricted shares subject to repurchase: Shares issued to founders — 6,250 Shares issued pursuant to the 2012 Stock Option and Grant Plan 992,176 1,091,038 Total restricted shares subject to repurchase 992,176 1,097,288 Liability pertaining to restricted shares subject to repurchase Other liabilities, current 703 677 Other liabilities, noncurrent 1,278 1,470 Total liabilities pertaining to shares subject to repurchase $ 1,981 $ 2,147

Stock-based Awards (Tables)

Stock-based Awards (Tables)	3 Months Ended
	Mar. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock option activity	The following summarizes option activity under the 2015 Plan and the 2012 Plan: Number of Options Weighted- Average Exercise Price Weighted- Average remaining contractual term (years) Aggregate Intrinsic Value (in thousands) Balance Outstanding, December 31, 2015 2,058,787 $ 8.71 9.0 Options granted 606,425 $ 15.09 Options exercised (42,266 ) $ 0.53 Options canceled (135,572 ) $ 22.10 Balance Outstanding, March 31, 2016 2,487,374 $ 9.67 9.0 $ 21,586 Exercisable, March 31, 2016 482,249 $ 3.96 8.2 $ 6,131 Vested and expected to vest, March 31, 2016 2,334,962 $ 9.50 9.0 $ 20,555
Fair value assumptions of stock option awards and performance-contingent awards	The fair values of stock options granted to employees were calculated using the following assumptions: Three Months Ended 2016 2015 Expected term (in years) 5.8-6.1 6.0-6.1 Volatility 79.4%-81.0% 75.9%-77.0% Risk-free interest rate 1.3%-1.9% 1.5%-1.7% Dividend yield — —
Stock-based compensation expense recognized	Total stock-based compensation recognized by function was as follows (in thousands): Three Months Ended 2016 2015 Research and development $ 545 $ 265 General and administrative 722 57 Total stock-based compensation expense $ 1,267 $ 322 Total stock-based compensation recognized for employees and non-employees was as follows (in thousands): Three Months Ended 2016 2015 Employee options and restricted stock awards $ 1,200 $ 293 Non-employee options 67 29 Total stock-based compensation expense $ 1,267 $ 322
Unrecognized stock-based compensation cost	As of March 31, 2016 the unrecognized stock-based compensation cost, net of expected forfeitures, and the estimated weighted-average amortization period, using the straight-line attribution method, was as follows (in thousands, except amortization period): Unrecognized Compensation Cost Weighted-average remaining amortization period (years) Options $ 14,022 2.9 Restricted stock awards 828 2.3 ESPP 215 0.2 Total unrecognized stock-based compensation expense $ 15,065

Net Loss per Share Attributab19

Net Loss per Share Attributable to Common Stockholders (Tables)	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Computation of basic and diluted net loss per share	The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders during the three months ended March 31, 2016 and 2015 , respectively (in thousands, except share and per share data): Three Months Ended 2016 2015 Numerator: Net loss $ (16,600 ) $ (7,417 ) Accretion and dividends on redeemable convertible preferred stock — (1,240 ) Net loss attributable to common stockholders $ (16,600 ) $ (8,657 ) Denominator: Weighted average common shares outstanding 29,441,404 2,052,874 Net loss per share attributable to common stockholders, basic and diluted $ (0.56 ) $ (4.22 )
Potentially dilutive securities that were not included in diluted per share calculations	Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Three Months Ended 2016 2015 Redeemable convertible preferred stock as if converted — 19,746,614 Options to purchase common stock 2,487,374 1,190,051 Restricted stock subject to future vesting 992,176 985,338 2015 ESPP 58,921 — Total 3,538,471 21,922,003

Organization and Basis of Pre20

Organization and Basis of Presentation (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016USD ($)segment	Dec. 31, 2015USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments | segment	1
Accumulated deficit | $	$ (115,065)	$ (98,465)

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	$ 134,124	$ 148,642
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	134,124	148,642
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	134,124	148,642
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	134,124	148,642
Money market funds | Level 1 | Restricted cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	$ 140	$ 140

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 4,637	$ 4,216
Less: accumulated depreciation and amortization	(2,344)	(2,102)
Property and equipment, net	2,293	2,114
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	3,275	3,151
Computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	930	596
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	348	340
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 84	$ 129

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Balance Sheet Components [Abstract]
Accrued clinical and manufacturing expenses	$ 4,089	$ 4,025
Accrued professional and consulting services	646	287
Other	3	88
Total accrued liabilities	$ 4,738	$ 4,400

Balance Sheet Components - Othe

Balance Sheet Components - Other Liabilities, Noncurrent (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Balance Sheet Components [Abstract]
Restricted shares subject to repurchase, noncurrent	$ 1,278	$ 1,470
Deferred rent, noncurrent	76	86
Total other liabilities, noncurrent	$ 1,354	$ 1,556

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock (Details)	Mar. 31, 2016shares
Class of Stock [Line Items]
Shares reserved for future issuance (shares)	5,970,934
Restricted Stock
Class of Stock [Line Items]
Shares reserved for future issuance (shares)	992,176
Stock Options
Class of Stock [Line Items]
Shares reserved for future issuance (shares)	2,487,374
Options Available for Future Grants
Class of Stock [Line Items]
Shares reserved for future issuance (shares)	2,379,284
Employee stock purchase plan
Class of Stock [Line Items]
Shares reserved for future issuance (shares)	112,100

Stockholders' Equity - Restrict

Stockholders' Equity - Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	May. 31, 2012	Mar. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Total restricted shares subject to repurchase (in shares)		992,176	1,097,288
Total liabilities pertaining to shares subject to repurchase		$ 1,981	$ 2,147
Other liabilities, current
Class of Stock [Line Items]
Total liabilities pertaining to shares subject to repurchase		703	677
Other liabilities, noncurrent
Class of Stock [Line Items]
Total liabilities pertaining to shares subject to repurchase		$ 1,278	$ 1,470
Restricted Stock | 2012 Stock Option and Grant Plan
Class of Stock [Line Items]
Shares issued pursuant to the 2012 Stock Option and Grant Plan (in shares)		992,176	1,091,038
Restricted Stock | Founders
Class of Stock [Line Items]
Shares issued to founders (in shares)	1,345,709
Exercise price (usd per share)	$ 0.0035
Shares issued to founders (in shares)		0	6,250

Stock-based Awards - Plan Summa

Stock-based Awards - Plan Summary (Details) - shares	Mar. 31, 2016	Jul. 31, 2015
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized for issuance (shares)		1,430,000
Options available for future grants	2,379,284
2015 ESPP | ESPP
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized for issuance (shares)		50,000

Stock-based Awards - Stock Opti

Stock-based Awards - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2014
Number of Options
Beginning balance, outstanding (shares)	2,058,787
Options granted (shares)	606,425
Options exercised (shares)	(42,266)
Options canceled (shares)	(135,572)
Ending balance, outstanding (shares)	2,487,374
Exercisable, number of options (shares)	482,249
Vested and expected to vest, number of options (shares)	2,334,962
Weighted- Average Exercise Price
Beginning balance, outstanding (usd per share)	$ 8.71
Options granted (usd per share)	15.09
Options exercised (usd per share)	0.53
Options canceled (usd per share)	22.10
Ending balance, outstanding (usd per share)	9.67
Exercisable, weighted-average exercise price (usd per share)	3.96
Vested and expected to vest, weighted-average exercise price (usd per share)	$ 9.50
Outstanding, weighted-average remaining contractual term	9 years	9 years
Exercisable, weighted-average remaining contractual term	8 years 2 months 12 days
Vested and expected to vest, weighted-average remaining contractual term	9 years
Balance outstanding, aggregate intrinsic value	$ 21,586
Exercisable, aggregate intrinsic value	6,131
Vested and expected to vest, aggregate intrinsic value	$ 20,555

Stock-based Awards - Valuation

Stock-based Awards - Valuation Assumptions for Stock Awards (Details) - Stock Options	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award
Volatility, minimum	79.40%	75.90%
Volatility, maximum	81.00%	77.00%
Risk-free interest rate, minimum	1.30%	1.50%
Risk-free interest rate, maximum	1.90%	1.70%
Dividend yield	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Expected term (in years)	5 years 9 months 18 days	6 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days

Stock-based Awards - Performanc

Stock-based Awards - Performance-Contingent and Market-Condition Awards (Details)	Aug. 17, 2015	Apr. 09, 2015USD ($)milestone$ / sharesshares	Mar. 31, 2016USD ($)milestone$ / sharesshares	Mar. 31, 2015USD ($)
Share-based Compensation Arrangement by Share-based Payment Award
Options granted in period (shares)			606,425
Exercise price of options granted (usd per share) | $ / shares			$ 15.09
Compensation expense recognized | $			$ 1,267,000	$ 322,000
Performance Awards | Senior Management
Share-based Compensation Arrangement by Share-based Payment Award
Grants in period (shares)		326,424
Number of operating milestones for performance vesting (in milestone) | milestone		4
Performance-Contingent Options | Senior Management
Share-based Compensation Arrangement by Share-based Payment Award
Options granted in period (shares)		227,139
Exercise price of options granted (usd per share) | $ / shares		$ 3.40
Number of operating milestones achieved (in milestone) | milestone			1
Compensation expense recognized | $			$ 100,000
Performance Contingent Restricted Stock | Senior Management
Share-based Compensation Arrangement by Share-based Payment Award
Restricted shares granted in period (shares)		99,285
Exercise price of restricted shares granted (usd per share) | $ / shares		$ 3.40
Restricted Stock | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award
Restricted shares granted in period (shares)		99,285
Minimum market capitalization | $		$ 2,000,000,000
Minimum consecutive trading days for market capitalization		20 days
Weighted-average grant date fair value of restricted shares (usd per share) | $ / shares		$ 0.70
Expiration period from IPO	24 months
Expected term (in years)		2 years 5 months

Stock-based Awards - Stock-base

Stock-based Awards - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,267	$ 322
Employee
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,200	293
Non-employee
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	67	29
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	545	265
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 722	$ 57

Stock-based Awards - Unrecogniz

Stock-based Awards - Unrecognized Stock-based Compensation Expense (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016USD ($)
Share-based Compensation Arrangement by Share-based Payment Award
Total unrecognized compensation cost	$ 15,065
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Unrecognized compensation cost, options	$ 14,022
Weighted-average remaining amortization period	2 years 10 months 24 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award
Unrecognized compensation cost, restricted stock awards	$ 828
Weighted-average remaining amortization period	2 years 3 months 18 days
ESPP
Share-based Compensation Arrangement by Share-based Payment Award
Unrecognized compensation cost, restricted stock awards	$ 215
Weighted-average remaining amortization period	2 months 12 days

Net Loss per Share Attributab33

Net Loss per Share Attributable to Common Stockholders - Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net loss	$ (16,600)	$ (7,417)
Accretion and dividends on redeemable convertible preferred stock	0	(1,240)
Net loss attributable to common stockholders	$ (16,600)	$ (8,657)
Denominator:
Weighted average common shares outstanding (shares)	29,441,404	2,052,874
Net loss per share attributable to common stockholders, basic and diluted (usd per share)	$ (0.56)	$ (4.22)

Net Loss per Share Attributab34

Net Loss per Share Attributable to Common Stockholders - Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Antidilutive Securities
Antidilutive securities excluded from earnings per share	3,538,471	21,922,003
Redeemable convertible preferred stock as converted
Antidilutive Securities
Antidilutive securities excluded from earnings per share	0	19,746,614
Options to purchase common stock
Antidilutive Securities
Antidilutive securities excluded from earnings per share	2,487,374	1,190,051
Restricted stock subject to future vesting
Antidilutive Securities
Antidilutive securities excluded from earnings per share	992,176	985,338
Employee stock purchase plan
Antidilutive Securities
Antidilutive securities excluded from earnings per share	58,921	0

Related Party Transactions (Det

Related Party Transactions (Details)	3 Months Ended
	Mar. 31, 2016USD ($)board_member	Mar. 31, 2015USD ($)
Related Party Transaction
Related party expenses	$ 0	$ 53,000
Third Rock Ventures | Board Members that are partners in TRV
Related Party Transaction
Number of board members | board_member	2
Third Rock Ventures | Management and Advisory Services
Related Party Transaction
Related party expenses	$ 0	$ 53,000