Kineta (KANT) 10-Q 13 May 16 2016 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2016	May. 12, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1
Trading Symbol	PTI
Entity Registrant Name	PROTEOSTASIS THERAPEUTICS, INC.
Entity Central Index Key	1,445,283
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		19,139,486

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 49,807	$ 13,844
Accounts receivable	136	918
Other current assets	824	180
Total current assets	50,767	14,942
Property and equipment, net	524	566
Deferred offering costs		2,744
Other assets	123	144
Restricted cash	294	294
Total assets	51,708	18,690
Current liabilities:
Accounts payable	3,207	3,330
Accrued expenses	1,172	2,248
Deferred revenue	4,028	4,076
Deferred rent	187	182
Total current liabilities	8,594	9,836
Deferred revenue, net of current portion	3,292	4,265
Deferred rent, net of current portion	240	287
Preferred stock warrant liability		110
Derivative liability	57	2
Total liabilities	$ 12,183	$ 14,500
Commitments and contingencies
Convertible preferred stock, (Series A and B), $0.001 par value; 0 and 110,057,398 shares authorized as of March 31, 2016 and December 31, 2015, respectively; 0 and 104,854,769 shares issued and outstanding as of March 31, 2016 and December 31, 2015, respectively; aggregate liquidation preference of $0 and $149,392, respectively, as of March 31, 2016 and December 31, 2015		$ 112,292
Stockholders' equity (deficit):
Common stock, $0.001 par value; 125,000,000 and 170,000,000 shares authorized as of March 31, 2016 and December 31, 2015, respectively; 19,139,041 and 571,137 shares issued and outstanding as of March 31, 2016 and December 31, 2015, respectively	$ 20	1
Additional paid-in capital	167,714	12,115
Accumulated deficit	(128,209)	(120,218)
Total stockholders' equity (deficit)	39,525	(108,102)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 51,708	$ 18,690

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Convertible preferred stock (Series A and B), par value	$ 0.001	$ 0.001
Convertible preferred stock (Series A and B), shares authorized	0	110,057,398
Convertible preferred stock (Series A and B), shares issued	0	104,854,769
Convertible preferred stock (Series A and B), shares outstanding	0	104,854,769
Convertible preferred stock (Series A and B), aggregate liquidation preference	$ 0	$ 149,392
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	170,000,000
Common stock, shares issued	19,139,041	571,137
Common stock, shares outstanding	19,139,041	571,137

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Revenue	$ 1,158	$ 807
Operating expenses:
Research and development	6,876	4,503
General and administrative	2,301	1,321
Total operating expenses	9,177	5,824
Loss from operations	(8,019)	(5,017)
Interest expense		(201)
Other income (expense), net	28	(522)
Net loss and comprehensive loss	(7,991)	(5,740)
Accruing dividends on preferred stock	(1,378)	(2,087)
Net loss attributable to common stockholders	$ (9,369)	$ (7,827)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.87)	$ (14.68)
Weighted average common shares outstanding-basic and diluted	10,766,722	533,097

Statements of Convertible Prefe

Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - 3 months ended Mar. 31, 2016 - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2015	$ (108,102)	$ 112,292	$ 1	$ 12,115	$ (120,218)
Beginning balance, shares at Dec. 31, 2015	571,137	104,854,769	571,137
Exercise of stock options	$ 41			41
Exercise of stock options, shares			17,344
Stock-based compensation expense	308			308
Issuance of common stock upon completion of initial public offering, net of offering costs	42,887		$ 6	42,881
Issuance of common stock upon completion of initial public offering, net of offering costs, shares			6,250,000
Conversion of convertible preferred stock to common stock	112,292	$ (112,292)	$ 10	112,282
Conversion of convertible preferred stock to common stock, shares		(104,854,769)	9,699,600
Issuance of common stock to settle accruing Series A dividends			$ 3	(3)
Issuance of common stock to settle accruing Series A dividends, Shares			2,590,742
Issuance of common stock for partial payment of accrued bonus	62			62
Issuance of common stock for partial payment of accrued bonus, shares			10,218
Conversion of preferred stock warrant to common stock warrant	28			28
Net loss	(7,991)				(7,991)
Ending balance at Mar. 31, 2016	$ 39,525		$ 20	$ 167,714	$ (128,209)
Ending balance, shares at Mar. 31, 2016	19,139,041		19,139,041

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Jun. 30, 2015	Mar. 31, 2015
Cash flows from operating activities:
Net loss	$ (7,991)		$ (5,740)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	66		62
Non-cash rent expense			67
Prepaid rent expense	(42)
Non-cash interest expense			201
Stock-based compensation expense	308	$ 478	438
Change in fair value of derivative liability	55		500
Change in fair value of preferred stock warrant liability	(82)		19
Changes in operating assets and liabilities:
Accounts receivable	782		(862)
Other current assets	(644)		(356)
Other assets	21		65
Accounts payable	957		(1,019)
Accrued expenses	(1,806)		621
Deferred revenue	(1,021)		1,474
Net cash used in operating activities	(8,397)		(4,530)
Cash flows from investing activities:
Purchases of property and equipment	(24)		(7)
Net cash used in investing activities	(24)		(7)
Cash flows from financing activities:
Proceeds from issuance of common stock upon completion of initial public offering, net of commissions and underwriting discounts	46,500
Proceeds from exercise of stock options	41		39
Payments of initial public offering costs	(2,157)
Net cash provided by financing activities	44,384		39
Net (decrease) increase in cash and cash equivalents	35,963		(4,498)
Cash and cash equivalents at beginning of period	13,844	$ 4,295	8,793
Cash and cash equivalents at end of period	49,807		4,295
Supplemental disclosure of non-cash investing and financing activities:
Conversion of convertible preferred stock into common stock	112,292
Issuance of common stock to settle accrued Series A preferred stock dividends	3
Issuance of common stock for partial payment of accrued bonus	62
Conversion of preferred stock warrants into common stock warrants	$ 28
Additions to property and equipment included in accounts payable or accrued expenses			101
Deferred offering costs included in accounts payable and accrued expenses			$ 52

Nature of the Business

Nature of the Business	3 Months Ended
	Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Proteostasis Therapeutics, Inc. (the “Company”) was incorporated in Delaware on December 13, 2006. The Company is an innovative biopharmaceutical company committed to the discovery and development of novel therapeutics that treat diseases caused by an imbalance in the proteostasis network, a set of pathways that control protein biosynthesis, folding, trafficking and clearance. The Company’s initial therapeutic focus is on cystic fibrosis, which is caused by defects in the cystic fibrosis transmembrane conductance regulator (“CFTR”) protein and insufficient CFTR protein function. The Company’s lead product candidate, PTI-428, is in early clinical development, and the Company’s other drug candidates are in the discovery phase. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. The Company’s financial statements have been prepared on the basis of continuity of operations, realization of assets, and the satisfaction of liabilities in the ordinary course of business. Through March 31, 2016, the Company has primarily funded its operations with proceeds received from its initial public offering, proceeds from the sale of convertible preferred stock and, to a lesser extent, payments received in connection with collaboration agreements and research grants. The Company has incurred losses and negative cash flows from operations and had an accumulated deficit of $128,209 as of March 31, 2016. The Company expects to continue to generate losses for the foreseeable future. As of March 31, 2016, the Company expects that its cash of $49,807 will be sufficient to fund its operating expenses and capital expenditure requirements through at least March 31, 2017. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. Reverse Stock Split On January 19, 2016, the Company effected a 1-for-10.8102 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s Preferred Stock. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios. Initial Public Offering In February 2016, the Company issued and sold 6,250,000 shares of its common stock in its initial public offering (“IPO”) at a public offering price of $8.00 per share, for net proceeds of $42,887 after deducting underwriting discounts and commissions of $3,500 and other offering expenses of $3,613. Upon the closing of the IPO, all shares of convertible preferred stock then outstanding converted into an aggregate of 9,699,600 shares of common stock, and the Company issued 2,590,742 shares of common stock as payment of $36,016 of accruing dividends due to holders of Series A preferred stock. In addition, the Company’s convertible preferred stock warrant outstanding at the close of the IPO converted to a warrant to purchase common stock. In connection with the completion of the IPO, the Company amended its certificate of incorporation to authorize the future issuance of up to 5,000,000 shares of undesignated preferred stock, par value $0.001 per share. As of March 31, 2016, there were no shares of preferred stock issued or outstanding. Unaudited Interim Financial Information The accompanying unaudited interim financial statements as of March 31, 2016 and for the three months ended March 31, 2016 and 2015 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 interim financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2015 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 30, 2016. The unaudited interim financial statements have been prepared on the same basis as the audited financial statements. In the opinion of management, the accompanying unaudited interim financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position as of March 31, 2016 and results of operations and cash flows for the three months ended March 31, 2016 and 2015. Such adjustments are of a normal and recurring nature. The results of operations for the three months ended March 31, 2016 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2016.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, revenue recognition, the accrual for research and development expenses and the valuation of common stock, preferred stock warrant liability and derivative liability. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs 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 offering. As of December 31, 2015, the Company had recorded $2,744 of deferred offering costs in contemplation of the Company’s initial public offering. On February 11, 2016, the Company reclassified $3,613 of deferred offering costs to additional paid-in capital as a reduction of the proceeds from the IPO. Restricted Cash At March 31, 2016 and December 31, 2015, restricted cash consisted of a certificate of deposit collateralizing a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate facilities. Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of March 31, 2016, the Company’s cash equivalents consisted of money market funds. 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 derivative liability and cash equivalents are carried at fair value determined according to the fair value hierarchy described above (see Note 3). The carrying value of cash equivalents, accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities. 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 February 10, 2016, the preferred stock warrant became a warrant to purchase common stock and the liability was remeasured at fair value and reclassified to additional paid-in capital. Net Loss per Share In February 2016, upon the closing of the IPO, all of the outstanding shares of the Company’s redeemable convertible preferred stock automatically converted into 9,699,600 shares of the Company’s common stock. Prior to this conversion, the Company followed the two-class method when computing net loss per share as the Company had issued shares that met the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable 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. Accordingly, the two-class method did not apply for periods in which the Company reported a net loss or a net loss attributable to common stockholders resulting from dividends or accretion related to its redeemable convertible preferred stock. Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Recently Issued Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In February 2016, the FASB issued ASU No. 2016-02, Leases In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing Topic 606

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s financial assets and liabilities 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 March 31, 2016 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 45,628 $ — $ — $ 45,628 $ 45,628 $ — $ — $ 45,628 Liabilities: Derivative liability $ — $ — $ 57 $ 57 $ — $ — $ 57 $ 57 Fair Value Measurements as of December 31, 2015 Using: Level 1 Level 2 Level 3 Total Liabilities: Derivative liability $ — $ — $ 2 $ 2 Preferred stock warrant liability — — 110 110 $ — $ — $ 112 $ 112 As of March 31, 2016, the Company’s cash equivalents, which were invested in money market funds, were valued based on Level 1 inputs. The Company did not hold any cash equivalents as of December 31, 2015. During the periods ended March 31, 2016 and December 31, 2015, there were no transfers between Level 1, Level 2 and Level 3. The warrant liability in the table above is comprised of the fair value of a warrant for the purchase of Series A preferred stock and is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. On February 10, 2016, upon the closing of the initial public offering the Series A preferred stock converted into common stock, the preferred stock warrant became exercisable for common stock instead of preferred stock, and the preferred stock warrant liability, was remeasured at the fair value at that time, then reclassified to additional paid-in capital. 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: As of February 10, As of December 31, 2016 2015 Expected term (in years) 2.25 2.5 Expected volatility 73.24% 59.12% Risk-free interest rate 0.74% 1.21% Expected dividend yield 8.0% 8.0% The fair value of the derivative liability is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of the derivative instrument was determined using the Monte-Carlo simulation analysis. In determining the fair value of the derivative liability, the inputs impacting fair value include the fair value of the Company’s common stock, expected term of the derivative instrument, expected volatility of the common stock price, risk-free interest rate, expected sales-based milestone payments, discount rate, probability of a change of control event, and the probability that the counterparty would elect to accept the alternative cash payment in lieu of its right to the future sales-based milestone payments. As of March 31, 2016, the Company determined the per share common stock price available based on publicly traded markets. As of December 31, 2015, the Company determined the per share fair value of the underlying stock price by taking into consideration recent business development and economic factors it deemed relevant. The Company determined the expected term of the instrument to be 2.50 years and 0.12 years as of March 31, 2016 and December 31, 2015, respectively. The Company estimated its expected stock volatility to be 76.9% and 74.1% as of March 31, 2016 and December 31, 2015, respectively, based on the historical volatility of publicly traded peer companies for terms matching the expected term of the instrument for each respective period. The risk-free interest rate was determined to be 0.80% and 0.14% as of March 31, 2016 and December 31, 2015, respectively, by reference to the U.S. Treasury yield curve for terms matching the expected term of the instrument for each respective period. The Company estimated the expected sales-based milestone payments based on four times the maximum research funding allowable under the CFFT collaboration agreement plus the expected achievement of certain milestones, which totaled $28,520 as of March 31, 2016 and December 31, 2015. The Company estimated the discount rate in the calculation of the present value of the expected future milestone payments to be 25% as of March 31, 2016 and December 31, 2015, based on expected returns of alternative investments of a similar type. The Company estimated the probability of a change of control event to be 5% and 10% as of March 31, 2016 and December 31, 2015, respectively, by taking into consideration recent developments within the Company. Changes in the values of the preferred stock warrant liability and the derivative liability are summarized below: Preferred Stock Derivative Warrant Liability Liability Fair value at December 31, 2015 $ 110 $ 2 Change in fair value (82 ) 55 Conversion to common stock warrant (28 ) — Fair value at March 31, 2016 $ — $ 57

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2016
Text Block [Abstract]
Accrued Expenses	4. Accrued Expenses Accrued expenses consisted of the following: March 31, December 31, 2016 2015 Accrued payroll and related expenses $ 711 $ 1,607 Accrued other 461 641 $ 1,172 $ 2,248

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	5. Stock-Based Compensation 2016 Stock Option and Incentive Plan On February 3, 2016, the Company’s stockholders approved the 2016 Stock Option and Incentive Plan (the “2016 Plan”), which became effective on February 9, 2016. The 2016 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards and other stock-based awards. The number of shares initially reserved for issuance under the 2016 Plan is 1,581,839 shares. The number of shares of common stock that may be issued under the 2016 Plan will automatically increase on each January 1, beginning on January 1, 2017, by the lesser of 3% of the shares of the Company’s common stock outstanding on the immediately preceding December 31 or an amount determined by the Company’s board of directors or the compensation committee of the board of directors. The shares of common stock underlying any awards that are forfeited, canceled, repurchased or are otherwise terminated by the Company under the 2016 Plan and the 2008 Plan will be added back to the shares of common stock available for issuance under the 2016 Plan. 2016 Employee Stock Purchase Plan On February 3, 2016, the Company’s stockholders approved the 2016 Employee Stock Purchase Plan (the “2016 ESPP”), which became effective in connection with the completion of the Company’s initial public offering. A total of 138,757 shares of common stock were reserved for issuance under this plan. In addition, the number of shares of common stock that may be issued under the 2016 ESPP will automatically increase on each January 1, beginning on January 1, 2017 and ending on January 1, 2026, by the least of (i) 138,757 shares of common stock, (ii) 1% of the Company’s shares of common stock outstanding on the immediately preceding December 31 and (iii) an amount determined by the Company’s board of directors or the compensation committee of the board of directors. Stock-Based Compensation The Company grants stock-based awards under the 2016 Plan and is authorized to issue common stock under the 2016 ESPP. The Company also has outstanding stock options under its 2008 Equity Incentive Plan but is no longer granting awards under this plan. As of March 31, 2016, 1,247,893 shares of common stock were available for issuance under the 2016 Plan. As of March 31, 2016, 138,757 shares of common stock were available for issuance to participating employees under the 2016 ESPP. Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows: Three Months Ended March 31, 2016 2015 Research and development $ 84 $ 391 General and administrative 224 47 $ 308 $ 438 Prior to 2013, the Company issued options to purchase 203,964 shares of common stock to non-employees, primarily members of the Company’s scientific advisory board, that vest upon the achievement of specified development and clinical milestones. As of March 31, 2016, options for the purchase of 83,250 shares held by non-employees remained unvested, pending achievement of the specified milestones, and had an aggregate fair value of $742. During the three months ended March 31, 2016 and 2015, the Company did not grant any options to non-employees. For the three months ended March 31, 2016 the Company did not record any stock-based compensation expense for options granted to non-employees prior to 2013. For the three months ended March 31, 2015 the Company recorded stock-based compensation expense for options granted to non-employees prior to 2013 of $372. Stock-based compensation expense for the three months ended June 30, 2015 was reduced by $478 for the cumulative correction of immaterial errors associated with the recognition of stock-based compensation for certain stock options with performance-based vesting conditions. Of this amount, $168 related to years prior to 2015 and $310 related to the three months ended March 31, 2015. Based upon its evaluation of relevant factors, the Company concluded that the uncorrected errors in its previously issued financial statements for any of the periods affected are immaterial and that the impact of recording the cumulative correction during the six months ended June 30, 2015 is not material to the Company’s results for the year ending December 31, 2015.

Collaboration Agreement

Collaboration Agreement	3 Months Ended
	Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration Agreement	6. Collaboration Agreement Biogen In December 2015, the Company commenced the third year of the research term under the Collaborative Research, Development, Commercialization and License Agreement (the “Biogen Agreement”) with Biogen New Ventures (“Biogen”). Under the original terms of the agreement, beginning in the third year and continuing through the fourth year of the research term, the Company is entitled to receive reimbursement of costs incurred for actual full-time equivalent employees conducting research under the Biogen agreement. During the first two years of the research term the Company received research funding payments on a guaranteed basis in the amount of $4,000. Payments received as reimbursement for actual costs incurred will be accounted for in the same manner as the guaranteed research funding payments, such that the payments will be recognized over the four-year research term of the agreement, which commenced in December 2013, with a cumulative catch-up for the elapsed research term being recognized at the time any such payments are earned.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	7. Income Taxes The Company did not provide for any income taxes in the three months ended March 31, 2016 or 2015. The Company had gross deferred tax assets of $46,562 at December 31, 2015 which increased by approximately $3,000 at March 31, 2016. The Company has provided a valuation allowance for the full amount of its net deferred tax assets because, at March 31, 2016 and December 31, 2015, it was more likely than not that any future benefit from deductible temporary differences and net operating loss and tax credit carryforwards would not be realized. The Company has not yet recorded any amounts for unrecognized tax benefits, interest or penalties historically through December 31, 2015. The Company files income tax returns in the U.S. federal and state jurisdictions in which it operates. The Company’s income tax returns are generally subject to tax examinations for the tax years ended December 31, 2012 to the present. There are currently no pending income tax examinations. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service and state tax authorities to the extent utilized in a future period.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Net Loss per Share	8. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Three Months Ended March 31, 2016 2015 Numerator: Net loss $ (7,991 ) $ (5,740 ) Accruing dividends on preferred stock (1,378 ) (2,087 ) Net loss attributable to common stockholders $ (9,369 ) $ (7,827 ) Denominator: Weighted average number of common shares outstanding—basic and diluted 10,766,722 533,097 Net loss per share attributable to common stockholders—basic and diluted $ (0.87 ) $ (14.68 ) The Company’s potential dilutive securities, which include stock options, convertible preferred stock and a warrant to purchase preferred stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: March 31, 2016 2015 Convertible preferred stock (as converted to common stock) — 20,944,249 Options to purchase common stock 1,655,853 908,460 Warrant for the purchase of convertible preferred stock (as converted to common stock) 14,800 44,406 1,670,653 21,897,115 In addition to the potentially dilutive securities noted above, as of March 31, 2015, the Company had outstanding convertible promissory notes for which principal and unpaid accrued interest due under the notes was automatically convertible into the class of the Company’s stock issued in the Company’s next qualified financing, as defined, based on a conversion price equal to the price per share paid by the investors in the financing. Because the necessary conditions for conversion of the notes had not been met as of March 31, 2015, the Company excluded these notes from the table above and the calculation of diluted net loss per share for the three months ended March 31, 2015. On September 2, 2015, and concurrent with the sale of Series B preferred stock, all outstanding convertible promissory notes and accrued interest thereon were automatically converted into shares of Series B preferred stock.

Nature of the Business (Policie

Nature of the Business (Policies)	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Reverse Stock Split	Reverse Stock Split On January 19, 2016, the Company effected a 1-for-10.8102 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s Preferred Stock. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios.
Initial Public Offering	Initial Public Offering In February 2016, the Company issued and sold 6,250,000 shares of its common stock in its initial public offering (“IPO”) at a public offering price of $8.00 per share, for net proceeds of $42,887 after deducting underwriting discounts and commissions of $3,500 and other offering expenses of $3,613. Upon the closing of the IPO, all shares of convertible preferred stock then outstanding converted into an aggregate of 9,699,600 shares of common stock, and the Company issued 2,590,742 shares of common stock as payment of $36,016 of accruing dividends due to holders of Series A preferred stock. In addition, the Company’s convertible preferred stock warrant outstanding at the close of the IPO converted to a warrant to purchase common stock. In connection with the completion of the IPO, the Company amended its certificate of incorporation to authorize the future issuance of up to 5,000,000 shares of undesignated preferred stock, par value $0.001 per share. As of March 31, 2016, there were no shares of preferred stock issued or outstanding.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying unaudited interim financial statements as of March 31, 2016 and for the three months ended March 31, 2016 and 2015 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 interim financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2015 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 30, 2016. The unaudited interim financial statements have been prepared on the same basis as the audited financial statements. In the opinion of management, the accompanying unaudited interim financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position as of March 31, 2016 and results of operations and cash flows for the three months ended March 31, 2016 and 2015. Such adjustments are of a normal and recurring nature. The results of operations for the three months ended March 31, 2016 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2016.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, revenue recognition, the accrual for research and development expenses and the valuation of common stock, preferred stock warrant liability and derivative liability. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs 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 offering. As of December 31, 2015, the Company had recorded $2,744 of deferred offering costs in contemplation of the Company’s initial public offering. On February 11, 2016, the Company reclassified $3,613 of deferred offering costs to additional paid-in capital as a reduction of the proceeds from the IPO.
Restricted Cash	Restricted Cash At March 31, 2016 and December 31, 2015, restricted cash consisted of a certificate of deposit collateralizing a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate facilities.
Cash Equivalents	Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of March 31, 2016, the Company’s cash equivalents consisted of money market funds.
Fair Value Measurements	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 derivative liability and cash equivalents are carried at fair value determined according to the fair value hierarchy described above (see Note 3). The carrying value of cash equivalents, accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities. 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 February 10, 2016, the preferred stock warrant became a warrant to purchase common stock and the liability was remeasured at fair value and reclassified to additional paid-in capital.
Net Loss per Share	Net Loss per Share In February 2016, upon the closing of the IPO, all of the outstanding shares of the Company’s redeemable convertible preferred stock automatically converted into 9,699,600 shares of the Company’s common stock. Prior to this conversion, the Company followed the two-class method when computing net loss per share as the Company had issued shares that met the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable 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. Accordingly, the two-class method did not apply for periods in which the Company reported a net loss or a net loss attributable to common stockholders resulting from dividends or accretion related to its redeemable convertible preferred stock. Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In February 2016, the FASB issued ASU No. 2016-02, Leases In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing Topic 606

Fair Value of Financial Asset16

Fair Value of Financial Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities 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 March 31, 2016 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 45,628 $ — $ — $ 45,628 $ 45,628 $ — $ — $ 45,628 Liabilities: Derivative liability $ — $ — $ 57 $ 57 $ — $ — $ 57 $ 57 Fair Value Measurements as of December 31, 2015 Using: Level 1 Level 2 Level 3 Total Liabilities: Derivative liability $ — $ — $ 2 $ 2 Preferred stock warrant liability — — 110 110 $ — $ — $ 112 $ 112
Assumptions and Inputs were Used in Determining Fair Value of Preferred Stock Warrant Liability	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: As of February 10, As of December 31, 2016 2015 Expected term (in years) 2.25 2.5 Expected volatility 73.24% 59.12% Risk-free interest rate 0.74% 1.21% Expected dividend yield 8.0% 8.0%
Summary of Changes in Values of Preferred Stock Warrant Liability and Derivative Liability	Changes in the values of the preferred stock warrant liability and the derivative liability are summarized below: Preferred Stock Derivative Warrant Liability Liability Fair value at December 31, 2015 $ 110 $ 2 Change in fair value (82 ) 55 Conversion to common stock warrant (28 ) — Fair value at March 31, 2016 $ — $ 57

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2016
Text Block [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following: March 31, December 31, 2016 2015 Accrued payroll and related expenses $ 711 $ 1,607 Accrued other 461 641 $ 1,172 $ 2,248

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock-Based Compensation Expense	Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows: Three Months Ended March 31, 2016 2015 Research and development $ 84 $ 391 General and administrative 224 47 $ 308 $ 438

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Three Months Ended March 31, 2016 2015 Numerator: Net loss $ (7,991 ) $ (5,740 ) Accruing dividends on preferred stock (1,378 ) (2,087 ) Net loss attributable to common stockholders $ (9,369 ) $ (7,827 ) Denominator: Weighted average number of common shares outstanding—basic and diluted 10,766,722 533,097 Net loss per share attributable to common stockholders—basic and diluted $ (0.87 ) $ (14.68 )
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share	The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: March 31, 2016 2015 Convertible preferred stock (as converted to common stock) — 20,944,249 Options to purchase common stock 1,655,853 908,460 Warrant for the purchase of convertible preferred stock (as converted to common stock) 14,800 44,406 1,670,653 21,897,115

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) $ / shares in Units, $ in Thousands	Jan. 19, 2016	Feb. 29, 2016USD ($)$ / sharesshares	Mar. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)
Nature Of Business [Line Items]
Accumulated deficit			$ 128,209	$ 120,218
Cash and cash equivalents			$ 49,807	$ 13,844
Reverse stock split description			On January 19, 2016, the Company effected a 1-for-10.8102 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company's Preferred Stock.
Reverse stock split ratio	10.8102
Reverse stock split effective date			Jan. 19, 2016
Proceeds from stock issuance, net of underwriting discounts and commissions			$ 46,500
Number of shares converted | shares		9,699,600
Number shares issued in share conversion | shares		2,590,742
IPO [Member]
Nature Of Business [Line Items]
Common stock issued and sold | shares		6,250,000
Common stock price per share | $ / shares		$ 8
Proceeds from stock issuance, net of underwriting discounts and commissions		$ 42,887
Underwriting discounts and commissions		3,500
Other offering expenses		3,613
Preferred stock, authorize for future issuance | shares			5,000,000
Preferred stock, par value | $ / shares			$ 0.001
Preferred stock, issued | shares			0
Preferred stock, outstanding | shares			0
Series A Preferred Stock [Member]
Nature Of Business [Line Items]
Accrued dividends		$ 36,016

Summary of Significant Accoun21

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Feb. 11, 2016	Feb. 29, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Deferred offering costs			$ 2,744
Payment of offering costs	$ 3,613
Number of common shares issued on conversion of convertible preferred stock		9,699,600

Fair Value of Financial Asset22

Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Assets:
Cash equivalents		$ 0
Liabilities:
Derivative liability	$ 57,000	2,000
Preferred stock warrant liability		110,000
Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	45,628,000
Total assets	45,628,000
Liabilities:
Derivative liability	57,000	2,000
Preferred stock warrant liability		110,000
Total liabilities	57,000	112,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	45,628,000
Total assets	45,628,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities:
Derivative liability	57,000	2,000
Preferred stock warrant liability		110,000
Total liabilities	$ 57,000	$ 112,000

Fair Value of Financial Asset23

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Cash equivalents		$ 0
Transfer of assets from level 1 to level 2	$ 0	0
Transfer of assets from level 2 to level 1	0	0
Transfer of liabilities from level 1 to level 2	0	0
Transfer of liabilities from level 2 to level 1	$ 0	$ 0
Expected term	2 years 6 months	1 month 13 days
Expected volatility	76.90%	74.10%
Risk-free interest rate	0.80%	0.14%
Expected sales-based milestone payments	$ 28,520,000	$ 28,520,000
Percentage of expected future milestone payments	25.00%	25.00%
Estimated probability of change of control event	5.00%	10.00%

Fair Value of Financial Asset24

Fair Value of Financial Assets and Liabilities - Assumptions and Inputs were Used in Determining Fair Value of Preferred Stock Warrant Liability (Detail)	Feb. 10, 2016	Dec. 31, 2015	Mar. 31, 2016	Dec. 31, 2015
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Expected term (in years)			2 years 6 months	1 month 13 days
Expected volatility			76.90%	74.10%
Risk-free interest rate			0.80%	0.14%
Preferred Stock Warrant Liability [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Expected term (in years)	2 years 3 months	2 years 6 months
Expected volatility	73.24%	59.12%
Risk-free interest rate	0.74%	1.21%
Expected dividend yield	8.00%	8.00%

Fair Value of Financial Asset25

Fair Value of Financial Assets and Liabilities - Summary of Changes in Values of Preferred Stock Warrant Liability and Derivative Liability (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Fair value, Beginning Balance	$ 110
Change in fair value	(82)	$ 19
Conversion to common stock warrant	(28)
Fair value, Beginning Balance	2
Change in fair value	55
Fair value, Ending Balance	$ 57

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Accrued payroll and related expenses	$ 711	$ 1,607
Accrued other	461	641
Total accrued expenses	$ 1,172	$ 2,248

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	Feb. 03, 2016	Mar. 31, 2016	Jun. 30, 2015	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 308,000	$ 478,000	$ 438,000
Prior to 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				168,000
Adjustments For Immaterial Errors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 310,000
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options unvested		83,250
Fair value of option		$ 742,000
Stock option grants		0		0
Non-Employees [Member] | Prior to 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option issued to purchase common stock		203,964
Stock-based compensation expense		$ 0		$ 372,000
2016 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	1,581,839
Common stock reserved for issuance, percentage of number of shares of common stock outstanding	3.00%
Common stock available for issuance		1,247,893
2016 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	138,757
Common stock reserved for issuance, percentage of number of shares of common stock outstanding	1.00%
Common stock available for issuance		138,757

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 308	$ 438
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	84	391
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 224	$ 47

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Biogen Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research funding payments on guaranteed basis	$ 4,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0	$ 0
Gross deferred tax assets			$ 46,562,000
Increase in gross deferred tax assets	$ 3,000,000
Amounts for unrecognized tax benefits, interest or penalties			$ 0

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net loss	$ (7,991)	$ (5,740)
Accruing dividends on preferred stock	(1,378)	(2,087)
Net loss attributable to common stockholders	$ (9,369)	$ (7,827)
Denominator:
Weighted average number of common shares outstanding-basic and diluted	10,766,722	533,097
Net loss per share attributable to common stockholders-basic and diluted	$ (0.87)	$ (14.68)

Net Loss per Share - Schedule32

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	1,670,653	21,897,115
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	1,655,853	908,460
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding		20,944,249
Warrants to Purchase Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	14,800	44,406