Kineta (KANT) 10-Q 4 Aug 17 2017 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Aug. 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
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		25,101,895

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 23,923	$ 18,613
Short-term investments	33,772	66,897
Restricted cash	294
Accounts receivable	730	668
Prepaids and other current assets	2,767	4,059
Total current assets	61,486	90,237
Property and equipment, net	522	541
Other assets	50	68
Restricted cash, net of current portion		294
Total assets	62,058	91,140
Current liabilities:
Accounts payable	2,321	2,021
Accrued expenses	6,145	4,328
Deferred revenue	2,227	2,204
Deferred rent	191	201
Total current liabilities	10,884	8,754
Deferred revenue, net of current portion		752
Deferred rent, net of current portion		87
Derivative liability	18	91
Total liabilities	10,902	9,684
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized as of June 30, 2017 and December 31, 2016, respectively; no shares issued and outstanding as of June 30, 2017 and December 31, 2016
Common stock, $0.001 par value; 125,000,000 shares authorized as of June 30, 2017 and December 31, 2016, respectively; 25,049,250 and 25,000,734 shares issued and outstanding as of June 30, 2017 and December 31, 2016, respectively	26	26
Additional paid-in capital	240,661	238,902
Accumulated other comprehensive loss	(27)	(22)
Accumulated deficit	(189,504)	(157,450)
Total stockholders’ equity	51,156	81,456
Total liabilities and stockholders’ equity	$ 62,058	$ 91,140

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	25,049,250	25,000,734
Common stock, shares outstanding	25,049,250	25,000,734

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenue	$ 1,147	$ 1,451	$ 2,168	$ 2,609
Operating expenses:
Research and development	15,370	7,404	28,478	14,280
General and administrative	2,902	3,115	6,072	5,416
Total operating expenses	18,272	10,519	34,550	19,696
Loss from operations	(17,125)	(9,068)	(32,382)	(17,087)
Interest income	169	20	360	20
Other income (expense), net	(2)	(5)	(32)	23
Net loss	(16,958)	(9,053)	(32,054)	(17,044)
Accruing dividends on preferred stock				(1,378)
Net loss attributable to common stockholders	$ (16,958)	$ (9,053)	$ (32,054)	$ (18,422)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.68)	$ (0.47)	$ (1.28)	$ (1.23)
Weighted average common shares outstanding—basic and diluted	25,040,131	19,139,183	25,030,291	14,953,022

Statements of Comprehensive Los

Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (16,958)	$ (9,053)	$ (32,054)	$ (17,044)
Other comprehensive loss:
Unrealized gain (loss) on investments	11		(5)
Comprehensive loss	$ (16,947)	$ (9,053)	$ (32,059)	$ (17,044)

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net loss	$ (32,054)	$ (17,044)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	136	142
Premium on short-term investments	(100)
Amortization of premium on short-term investments	137
Non-cash rent expense	(97)	(87)
Stock-based compensation expense	1,353	805
Stock issued for consulting services	382
Change in fair value of derivative liability	(73)	89
Change in fair value of preferred stock warrant liability		(82)
Gain on disposal of property and equipment		(13)
Changes in operating assets and liabilities:
Accounts receivable	(62)	778
Prepaids and other current assets	1,292	(939)
Other assets	18	42
Accounts payable	289	1,491
Accrued expenses	1,817	1,079
Deferred revenue	(729)	(1,472)
Net cash used in operating activities	(27,691)	(15,211)
Cash flows from investing activities:
Purchases of short-term investments	(18,730)
Proceeds received from maturities of short-term investments	51,813
Purchases of property and equipment	(106)	(32)
Proceeds received from disposal of property and equipment		13
Net cash provided by (used in) investing activities	32,977	(19)
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	24	43
Payments of public offering costs		(2,515)
Net cash provided by financing activities	24	44,028
Net increase in cash and cash equivalents	5,310	28,798
Cash and cash equivalents at beginning of period	18,613	13,844
Cash and cash equivalents at end of period	23,923	42,642
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	$ 11

Nature of the Business

Nature of the Business	6 Months Ended
	Jun. 30, 2017
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 candidates, PTI-428 and PTI-801, are in early clinical development, and the Company’s other drug candidates are in the early clinical, preclinical development and discovery phases. As of December 31, 2016, the Company adopted the provisions of Financial Statement Account Standards Board (FASB) Accounting Standard Codification (ASC) Topic 205-40, Presentation of Financial Statements – Going Concern requires management to 1) identify and disclose if there are initial conditions indicating substantial doubt about the Company’s ability to continue as a going concern within twelve months of the issuance date of the financial statements, 2) disclose the principal conditions that gave rise to substantial doubt, 3) disclose management’s evaluation of the significance of those conditions in relation to the Company’s ability to meet its obligations and 4) disclose management’s plans that are intended to mitigate the adverse conditions. In accordance with the accounting standard, when considering management’s plans to mitigate the conditions giving rise to substantial doubt, management can only consider those plans which are probable to be successfully implemented The Company has incurred losses from operations since its inception. As of June 30, 2017, the Company had an accumulated deficit of $189.5 million. During the three and six months ended June 30, 2017, the Company incurred losses of $17.0 million and $32.1 million and during the six months ended June 30, 2017 the Company used $27.7 million of cash in operations. The Company expects to continue to generate operating losses in the foreseeable future. The Company currently expects that its cash, cash equivalents and short-term investments of $57.7 million will be sufficient to fund its operating expenses and capital requirements, based upon its current operating plan, through the second quarter of 2018. As of June 30, 2017, management has further assessed this risk and, in accordance with the requirements of ASC 205-40, determined that there are initial conditions indicating that there is substantial doubt about the Company’s ability to continue as a going concern within twelve months of the issuance date of these condensed financial statements. These indicators are the Company’s accumulated deficit and the forecasted cash expenditures. As such, under the requirements of ASC 205-40, management may not consider the potential for future capital raises in their assessment of the Company’s ability to meet its obligations for the next twelve months. If the Company is unable to obtain funding, the Company would 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, or the Company may be unable to continue operations. The ability to reduce spending at a level that mitigates the factors described above, is not considered probable, as defined in the accounting standards; as such, under the requirements of ASC 205-40, the full extent to which management may extend the Company’s funds through these actions may not be considered in management’s assessment of the Company’s ability to continue as a going concern for the next twelve months. Thus, in accordance with the requirements of ASC 205-40, management has concluded that it is required to disclose that substantial doubt exists about the Company’s ability to continue as a going concern for twelve months from the date these condensed financial statements are issued. While management has plans in place to mitigate these actions, they are not considered probable, as defined in the accounting standards, and a failure to raise the additional funding or to effectively implement cost reductions could harm the Company’s business, results of operations and future prospects. The condensed financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates continuity of operations, the realization of assets and the satisfaction of liabilities and commitments in the normal course of business .

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Unaudited Interim Financial Information The condensed balance sheet at December 31, 2016 was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed financial statements as of June 30, 2017 and for the three and six months ended June 30, 2017 are unaudited. The accompanying unaudited interim financial statements 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 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 unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2016 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 30, 2017. In the opinion of management, all adjustments, consisting only of normal recurring adjustments as necessary, for the fair statement of the Company’s condensed financial position as of June 30, 2017 and condensed results of its operations and cash flows for the three and six months ended June 30, 2017 have been made. The results of operations for three and six months ended June 30, 2017 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2017. 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 and the 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. Restricted Cash As of June 30, 2017 and December 31, 2016, 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 June 30, 2017 and December 31, 2016, the Company’s cash equivalents consisted of money market funds and U.S. government-sponsored enterprise securities. Short-term Investments Short-term investments represent holdings of available-for-sale marketable securities in accordance with the Company’s investment policy and cash management strategy. Short-term investments mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses, net of taxes, reported as a component of stockholders’ equity until realized or until a determination is made that an other-than-temporary decline in market value has occurred. The cost of marketable securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other expense, net. 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, short-term investments and cash equivalents are carried at fair value determined according to the fair value hierarchy described above (see Note 4). The carrying value of cash and cash equivalents, accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities. 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 income (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. For any period in which the Company has reported net income, basic net income per common share attributable to common stockholders is adjusted for certain amounts to calculate diluted net loss per common share attributable to common stockholders, since dilutive common shares are assumed to have been issued if their effect is dilutive and not 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) (“ASU 2014-09”), which supersedes existing revenue recognition guidance under GAAP. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The standard defines a five-step process to achieve this principle, and will require companies to use more judgment and make more estimates than under the current guidance. The Company expects that these judgments and estimates will include identifying performance obligations in the customer contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which delays the effective date of ASU 2014-09 such that the standard is effective for public entities for annual periods beginning after December 15, 2017 and for interim periods within those fiscal years. Early adoption of the standard is permitted for annual periods beginning after December 15, 2016. In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing . The new standard clarifies two aspects of ASU 2014-09, Revenue from Contracts with Customers (Topic 606) : identifying performance obligations and the licensing implementation guidance. These new standards will become effective for the Company on January 1, 2018. The Company is currently evaluating the impact that the adoption of these new standards will have on its financial statements and related disclosures 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 . As a result, the Company has made an accounting policy election to account for forfeitures as they occur. The adoption of ASU 2016‑09 also requires excess tax benefits and tax deficiencies be recorded in the income statement as opposed to additional paid‑in capital when the awards vest or are settled. This had no material impact on the condensed financial statements as of and for the In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments . In May 2017, the FASB issued ASU 2017-09, Compensation – Stock Compensation (Topic 719): Scope of Modification Accounting

Short Term Investments

Short Term Investments	6 Months Ended
	Jun. 30, 2017
Cash Cash Equivalents And Short Term Investments [Abstract]
Short Term Investments	3. Short Term Investments The following table summarizes the Company’s short term investments as of June 30, 2017 and December 31, 2016 (in thousands): June 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 20,784 $ — $ (17 ) $ 20,767 U.S. treasury securities 13,015 — (10 ) 13,005 $ 33,799 $ — $ (27 ) $ 33,772 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 53,384 $ — $ (20 ) $ 53,364 U.S. treasury securities 13,535 — (2 ) 13,533 $ 66,919 $ — $ (22 ) $ 66,897 The Company did not have any realized gains or losses on its short-term investments for the three and six months ended June 30, 2017. There were no other-than-temporary impairments recognized for the three and six months ended June 30, 2017. The Company did not hold any short-term investments as of June 30, 2016, and therefore did not have any realized gains or losses or other-than-temporary impairments for the three and six months ended June 30, 2016.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	4. 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 (in thousands): Fair Value Measurements as of June 30, 2017 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 20,009 $ — $ — $ 20,009 U.S. government-sponsored enterprise securities — 1,999 — 1,999 Short-term investments: U.S. government-sponsored enterprise securities — 20,767 — 20,767 U.S. treasury securities — 13,005 — 13,005 $ 20,009 $ 35,771 $ — $ 55,780 Liabilities: Derivative liability $ — $ — $ 18 $ 18 $ — $ — $ 18 $ 18 Fair Value Measurements as of December 31, 2016 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 15,440 $ — $ — $ 15,440 Short-term investments: U.S. government-sponsored enterprise securities — 53,365 — 53,365 U.S. treasury securities — 13,532 — 13,532 $ 15,440 $ 66,897 $ — $ 82,337 Liabilities: Derivative liability $ — $ — $ 91 $ 91 $ — $ — $ 91 $ 91 During the periods ended June 30, 2017 and December 31, 2016, there were no transfers between Level 1, Level 2 and Level 3. Derivative Liability The derivative liability relates to a cash settlement option associated with the change of control provision in our Cystic Fibrosis Foundation Therapeutics, Inc. (“CFFT”) agreement, which meets the definition of a derivative. 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 June 30, 2017 and December 31, 2016, the Company determined the per share common stock price available based on the closing price of its common stock on the NASDAQ Global Market as of June 30, 2017. The Company determined the expected term of the instrument to be 2.50 years as of June 30, 2017 and December 31, 2016, respectively. The Company estimated its expected stock volatility to be 80.0% and 81.1% as of June 30, 2017 and December 31, 2016, 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 1.47% and 1.33% as of June 30, 2017 and December 31, 2016, respectively, by reference to the U.S. Treasury yield curve for terms matching the expected term of the instrument for each respective period. Changes in the values of the derivative liability are summarized below (in thousands): Derivative Liability Fair value at December 31, 2016 $ 91 Change in fair value (73 ) Fair value at June 30, 2017 $ 18

Prepaids and Other Current Asse

Prepaids and Other Current Assets	6 Months Ended
	Jun. 30, 2017
Prepaid Expense And Other Assets Current [Abstract]
Prepaids and Other Current Assets	5. Prepaids and Other Current Assets Prepaids and other current assets consisted of the following (in thousands): June 30, December 31, 2017 2016 Prepaid clinical, manufacturing and scientific expenses $ 1,720 $ 1,390 Prepaid insurance expenses 379 104 Other prepaid expenses and other current assets 668 2,565 $ 2,767 $ 4,059

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2017
Text Block [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following (in thousands): June 30, December 31, 2017 2016 Accrued payroll and related expenses $ 1,322 $ 1,813 Accrued research and development expenses 4,428 1,612 Accrued professional fees 291 383 Accrued other 104 520 $ 6,145 $ 4,328

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7. 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. As of June 30, 2017, the total number of shares reserved under the 2016 Plan and 2008 Plan was 3,630,575 and the Company had 1,040,017 shares available for future 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. As of June 30, 2017, the total number of shares reserved under the 2016 ESPP was 277,514 shares. The Company recognized less than $0.1 million of stock-based compensation during each of the three and six month periods ended June 30, 2017. Stock Option Grants and Shares to Non-employees 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 June 30, 2017, 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 $0.3 million. Stock-Based Compensation Stock-based compensation expense, including shares issued to a non-employee for consulting services, was classified in the statements of operations as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Research and development $ 403 $ 148 $ 658 $ 232 General and administrative 588 349 1,077 573 $ 991 $ 497 $ 1,735 $ 805

Collaboration Agreement

Collaboration Agreement	6 Months Ended
	Jun. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Agreement	8. Collaboration Agreement Astellas Under the Collaborative Research, Development, Commercialization and License Agreement (as further amended, the “Astellas Agreement”) with Astellas Pharma Inc. (“Astellas”), entered into in November 2014, the Company recognized revenue of $1.1 million and $0.8 million for the three months ended June 30, 2017 and 2016, respectively, and $2.2 million and $1.2 million for the six months ended June 30, 2017 and 2016, respectively. The Company recognizes revenue from all upfront payments, research funding payments, non-substantive milestone payments and reimbursements of third-party costs under this arrangement, together as a single unit, over the services being recognized at the time any non-substantive milestone payment or other consideration is earned. Amounts recorded as deferred revenue under the Astellas Agreement totaled $2.2 million and $3.0 million as of June 30, 2017 and December 31, 2016, respectively. Biogen Under the now-terminated collaboration agreement between the Company and Biogen New Ventures, formerly Biogen Idec New Ventures Inc. (“Biogen”), the Company recognized revenue of $0.7 million and $1.4 million for the three and six months ended June 30, 2016. The Company did not have any deferred revenue under the Biogen agreement as of June 30, 2017 and December 31, 2016 and will not recognize any additional revenue under this terminated agreement in the future.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Company did not record a federal or state income tax benefit for its losses for the three and six months ended June 30, 2017 and 2016 due to the conclusion that a full valuation allowance is required against the Company’s deferred tax assets.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2017
Earnings Per Share [Abstract]
Net Loss per Share	10. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Numerator: Net loss $ (16,958 ) $ (9,053 ) $ (32,054 ) $ (17,044 ) Accruing dividends on preferred stock — — — (1,378 ) Net loss attributable to common stockholders-basic and diluted $ (16,958 ) $ (9,053 ) $ (32,054 ) $ (18,422 ) Denominator: Weighted average number of common shares outstanding—basic 25,040,131 19,139,183 25,030,291 14,953,022 Net loss per share attributable to common stockholders—basic and diluted $ (0.68 ) $ (0.47 ) $ (1.28 ) $ (1.23 ) The Company’s potential dilutive securities, which include stock options and a warrant to purchase common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company has reported a net loss for all periods presented. Therefore, diluted net loss per common share is the same as basic net loss per common share. The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported June 30, 2017 2016 Options to purchase common stock 2,590,558 1,751,524 Warrant for the purchase of convertible preferred stock (as converted to common stock) — 14,800 2,590,558 1,766,324 The warrant for the purchase of common stock was exercised in February 2016. The Company issued 4,349 shares in a net issuance transaction.

Summary of Significant Accoun17

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Unaudited Interim Financial Information	Unaudited Interim Financial Information The condensed balance sheet at December 31, 2016 was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed financial statements as of June 30, 2017 and for the three and six months ended June 30, 2017 are unaudited. The accompanying unaudited interim financial statements 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 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 unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2016 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 30, 2017. In the opinion of management, all adjustments, consisting only of normal recurring adjustments as necessary, for the fair statement of the Company’s condensed financial position as of June 30, 2017 and condensed results of its operations and cash flows for the three and six months ended June 30, 2017 have been made. The results of operations for three and six months ended June 30, 2017 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2017.
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 and the 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.
Restricted Cash	Restricted Cash As of June 30, 2017 and December 31, 2016, 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 June 30, 2017 and December 31, 2016, the Company’s cash equivalents consisted of money market funds and U.S. government-sponsored enterprise securities.
Short-Term Investments	Short-term Investments Short-term investments represent holdings of available-for-sale marketable securities in accordance with the Company’s investment policy and cash management strategy. Short-term investments mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses, net of taxes, reported as a component of stockholders’ equity until realized or until a determination is made that an other-than-temporary decline in market value has occurred. The cost of marketable securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other expense, net.
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, short-term investments and cash equivalents are carried at fair value determined according to the fair value hierarchy described above (see Note 4). The carrying value of cash and cash equivalents, accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities.
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 income (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. For any period in which the Company has reported net income, basic net income per common share attributable to common stockholders is adjusted for certain amounts to calculate diluted net loss per common share attributable to common stockholders, since dilutive common shares are assumed to have been issued if their effect is dilutive and not 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) (“ASU 2014-09”), which supersedes existing revenue recognition guidance under GAAP. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The standard defines a five-step process to achieve this principle, and will require companies to use more judgment and make more estimates than under the current guidance. The Company expects that these judgments and estimates will include identifying performance obligations in the customer contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which delays the effective date of ASU 2014-09 such that the standard is effective for public entities for annual periods beginning after December 15, 2017 and for interim periods within those fiscal years. Early adoption of the standard is permitted for annual periods beginning after December 15, 2016. In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing . The new standard clarifies two aspects of ASU 2014-09, Revenue from Contracts with Customers (Topic 606) : identifying performance obligations and the licensing implementation guidance. These new standards will become effective for the Company on January 1, 2018. The Company is currently evaluating the impact that the adoption of these new standards will have on its financial statements and related disclosures 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 . As a result, the Company has made an accounting policy election to account for forfeitures as they occur. The adoption of ASU 2016‑09 also requires excess tax benefits and tax deficiencies be recorded in the income statement as opposed to additional paid‑in capital when the awards vest or are settled. This had no material impact on the condensed financial statements as of and for the In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments . In May 2017, the FASB issued ASU 2017-09, Compensation – Stock Compensation (Topic 719): Scope of Modification Accounting
Derivative Liability	Derivative Liability The derivative liability relates to a cash settlement option associated with the change of control provision in our Cystic Fibrosis Foundation Therapeutics, Inc. (“CFFT”) agreement, which meets the definition of a derivative. 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 June 30, 2017 and December 31, 2016, the Company determined the per share common stock price available based on the closing price of its common stock on the NASDAQ Global Market as of June 30, 2017. The Company determined the expected term of the instrument to be 2.50 years as of June 30, 2017 and December 31, 2016, respectively. The Company estimated its expected stock volatility to be 80.0% and 81.1% as of June 30, 2017 and December 31, 2016, 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 1.47% and 1.33% as of June 30, 2017 and December 31, 2016, respectively, by reference to the U.S. Treasury yield curve for terms matching the expected term of the instrument for each respective period. Changes in the values of the derivative liability are summarized below (in thousands): Derivative Liability Fair value at December 31, 2016 $ 91 Change in fair value (73 ) Fair value at June 30, 2017 $ 18

Short Term Investments (Tables)

Short Term Investments (Tables)	6 Months Ended
	Jun. 30, 2017
Cash Cash Equivalents And Short Term Investments [Abstract]
Summary of Short Term Investments	The following table summarizes the Company’s short term investments as of June 30, 2017 and December 31, 2016 (in thousands): June 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 20,784 $ — $ (17 ) $ 20,767 U.S. treasury securities 13,015 — (10 ) 13,005 $ 33,799 $ — $ (27 ) $ 33,772 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 53,384 $ — $ (20 ) $ 53,364 U.S. treasury securities 13,535 — (2 ) 13,533 $ 66,919 $ — $ (22 ) $ 66,897

Fair Value of Financial Asset19

Fair Value of Financial Assets and Liabilities (Tables)	6 Months Ended
	Jun. 30, 2017
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 (in thousands): Fair Value Measurements as of June 30, 2017 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 20,009 $ — $ — $ 20,009 U.S. government-sponsored enterprise securities — 1,999 — 1,999 Short-term investments: U.S. government-sponsored enterprise securities — 20,767 — 20,767 U.S. treasury securities — 13,005 — 13,005 $ 20,009 $ 35,771 $ — $ 55,780 Liabilities: Derivative liability $ — $ — $ 18 $ 18 $ — $ — $ 18 $ 18 Fair Value Measurements as of December 31, 2016 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 15,440 $ — $ — $ 15,440 Short-term investments: U.S. government-sponsored enterprise securities — 53,365 — 53,365 U.S. treasury securities — 13,532 — 13,532 $ 15,440 $ 66,897 $ — $ 82,337 Liabilities: Derivative liability $ — $ — $ 91 $ 91 $ — $ — $ 91 $ 91
Summary of Changes in Values of Derivative Liability	Changes in the values of the derivative liability are summarized below (in thousands): Derivative Liability Fair value at December 31, 2016 $ 91 Change in fair value (73 ) Fair value at June 30, 2017 $ 18

Prepaids and Other Current As20

Prepaids and Other Current Assets (Tables)	6 Months Ended
	Jun. 30, 2017
Prepaid Expense And Other Assets Current [Abstract]
Schedule of Prepaids and Other Current Assets	Prepaids and other current assets consisted of the following (in thousands): June 30, December 31, 2017 2016 Prepaid clinical, manufacturing and scientific expenses $ 1,720 $ 1,390 Prepaid insurance expenses 379 104 Other prepaid expenses and other current assets 668 2,565 $ 2,767 $ 4,059

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2017
Text Block [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands): June 30, December 31, 2017 2016 Accrued payroll and related expenses $ 1,322 $ 1,813 Accrued research and development expenses 4,428 1,612 Accrued professional fees 291 383 Accrued other 104 520 $ 6,145 $ 4,328

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-Based Compensation Expense, Including Shares Issued to Non-Employee for Consulting Services	Stock-based compensation expense, including shares issued to a non-employee for consulting services, was classified in the statements of operations as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Research and development $ 403 $ 148 $ 658 $ 232 General and administrative 588 349 1,077 573 $ 991 $ 497 $ 1,735 $ 805

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2017
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 (in thousands, except share and per share amounts): Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Numerator: Net loss $ (16,958 ) $ (9,053 ) $ (32,054 ) $ (17,044 ) Accruing dividends on preferred stock — — — (1,378 ) Net loss attributable to common stockholders-basic and diluted $ (16,958 ) $ (9,053 ) $ (32,054 ) $ (18,422 ) Denominator: Weighted average number of common shares outstanding—basic 25,040,131 19,139,183 25,030,291 14,953,022 Net loss per share attributable to common stockholders—basic and diluted $ (0.68 ) $ (0.47 ) $ (1.28 ) $ (1.23 )
Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted-average Shares Outstanding	The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported : June 30, 2017 2016 Options to purchase common stock 2,590,558 1,751,524 Warrant for the purchase of convertible preferred stock (as converted to common stock) — 14,800 2,590,558 1,766,324

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (189,504)		$ (189,504)		$ (157,450)
Cash, cash equivalents and short-term investments	57,700		57,700
Net loss	$ (16,958)	$ (9,053)	(32,054)	$ (17,044)
Cash in operations			$ 27,691	$ 15,211

Summary of Significant Accoun25

Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended
	Feb. 29, 2016shares
Accounting Policies [Abstract]
Number of common shares issued on conversion of convertible preferred stock	9,699,600

Short Term Investments - Summar

Short Term Investments - Summary of Short Term Investments (Detail) - USD ($)	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 33,799,000	$ 66,919,000
Gross Unrealized Losses	(27,000)	(22,000)
Fair Value	33,772,000	66,897,000	$ 0
U.S Government-Sponsored Enterprise Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,784,000	53,384,000
Gross Unrealized Losses	(17,000)	(20,000)
Fair Value	20,767,000	53,364,000
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,015,000	13,535,000
Gross Unrealized Losses	(10,000)	(2,000)
Fair Value	$ 13,005,000	$ 13,533,000

Short Term Investments - Additi

Short Term Investments - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Realized gains (losses) on short-term investments	$ 0	$ 0	$ 0	$ 0
Other-than-temporary impairments recognized	0	0	0	0
Short-term investments	$ 33,772,000	$ 0	$ 33,772,000	$ 0	$ 66,897,000

Fair Value of Financial Asset28

Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Liabilities:
Derivative liability	$ 18	$ 91
Fair Value, Measurements, Recurring [Member]
Assets:
Total assets	55,780	82,337
Liabilities:
Derivative liability	18	91
Total liabilities	18	91
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	20,009	15,440
Fair Value, Measurements, Recurring [Member] | U.S Government-Sponsored Enterprise Securities [Member]
Assets:
Cash equivalents	1,999
Short-term investments	20,767	53,365
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Assets:
Short-term investments	13,005	13,532
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Total assets	20,009	15,440
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	20,009	15,440
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Total assets	35,771	66,897
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S Government-Sponsored Enterprise Securities [Member]
Assets:
Cash equivalents	1,999
Short-term investments	20,767	53,365
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Treasury Securities [Member]
Assets:
Short-term investments	13,005	13,532
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Liabilities:
Derivative liability	18	91
Total liabilities	$ 18	$ 91

Fair Value of Financial Asset29

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
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
Fair value determination model	Monte-Carlo simulation analysis
Expected term	2 years 6 months	2 years 6 months
Expected volatility	80.00%	81.10%
Risk-free interest rate	1.47%	1.33%

Fair Value of Financial Asset30

Fair Value of Financial Assets and Liabilities - Summary of Changes in Values of Derivative Liability (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017USD ($)
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Fair value, Beginning Balance	$ 91
Derivative Liability, Change in fair value	(73)
Derivative Liability, Fair value, Ending Balance	$ 18

Prepaids and Other Current As31

Prepaids and Other Current Assets - Schedule of Prepaids and Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Prepaid Expense And Other Assets Current [Abstract]
Prepaid clinical, manufacturing and scientific expenses	$ 1,720	$ 1,390
Prepaid insurance expenses	379	104
Other prepaid expenses and other current assets	668	2,565
Prepaids and other current assets	$ 2,767	$ 4,059

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 1,322	$ 1,813
Accrued research and development expenses	4,428	1,612
Accrued professional fees	291	383
Accrued other	104	520
Total accrued expenses	$ 6,145	$ 4,328

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	Feb. 03, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation		$ 991,000	$ 497,000	$ 1,735,000	$ 805,000
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options unvested		83,250		83,250
Fair value of option				$ 300,000
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
2016 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	1,581,839	1,040,017		1,040,017
Common stock reserved for issuance, percentage of number of shares of common stock outstanding	3.00%
2016 Plan and 2008 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		3,630,575		3,630,575
2016 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	138,757	277,514		277,514
Common stock reserved for issuance, percentage of number of shares of common stock outstanding	1.00%
Common stock available for issuance		138,757		138,757
2016 ESPP [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation		$ 100,000		$ 100,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense, Including Shares Issued to Non-Employee for Consulting Services (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 991	$ 497	$ 1,735	$ 805
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	403	148	658	232
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 588	$ 349	$ 1,077	$ 573

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2015	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue		$ 1,147,000	$ 1,451,000	$ 2,168,000	$ 2,609,000
Astellas Collaboration Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue		1,100,000	800,000	2,200,000	1,200,000
Initial research term	3 years 6 months
Deferred revenue		2,200,000		2,200,000		$ 3,000,000
Biogen License Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue			$ 700,000		$ 1,400,000
Deferred revenue		$ 0		$ 0		$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Federal income tax benefit	$ 0	$ 0	$ 0	$ 0
State income tax benefit	$ 0	$ 0	$ 0	$ 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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss	$ (16,958)	$ (9,053)	$ (32,054)	$ (17,044)
Accruing dividends on preferred stock				(1,378)
Net loss attributable to common stockholders-basic and diluted	$ (16,958)	$ (9,053)	$ (32,054)	$ (18,422)
Denominator:
Weighted average number of common shares outstanding—basic	25,040,131	19,139,183	25,030,291	14,953,022
Net loss per share attributable to common stockholders—basic and diluted	$ (0.68)	$ (0.47)	$ (1.28)	$ (1.23)

Net Loss per Share - Schedule38

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted-average Shares Outstanding (Detail) - shares	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted weighted-average shares outstanding	2,590,558	1,766,324
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 weighted-average shares outstanding	2,590,558	1,751,524
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 weighted-average shares outstanding		14,800

Net Loss per Share - Additional

Net Loss per Share - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2017shares
Earnings Per Share [Abstract]
Shares issued in net issuance transaction	4,349