Histogen (HSTO) 10-K 16 Mar 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Mar. 01, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	CNAT
Entity Registrant Name	Conatus Pharmaceuticals Inc.
Entity Central Index Key	1,383,701
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		26,169,896
Entity Public Float			$ 36.6

Balance Sheets

Balance Sheets - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 58,083,409	$ 13,876,090
Marketable securities	18,931,715	22,632,019
Other receivables	2,500,000
Prepaid and other current assets	937,436	1,982,031
Total current assets	80,452,560	38,490,140
Property and equipment, net	261,446	344,734
Other assets	1,609,834	892,394
Total assets	82,323,840	39,727,268
Current liabilities:
Accounts payable and accrued expenses	5,311,093	2,545,894
Accrued compensation	2,351,703	1,436,804
Current portion of deferred revenue	30,897,192
Note payable	1,000,000
Total current liabilities	39,559,988	3,982,698
Deferred revenue, less current portion	20,803,762
Note payable		1,000,000
Deferred rent	171,544	204,224
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value; 200,000,000 shares authorized; 26,118,722 shares issued and outstanding at December 31, 2016; 19,877,857 shares issued and 19,845,611 shares outstanding, excluding 32,246 shares subject to repurchase, at December 31, 2015	2,612	1,984
Additional paid-in capital	172,424,531	155,441,280
Accumulated other comprehensive loss	(6,145)	(3,907)
Accumulated deficit	(150,632,452)	(120,899,011)
Total stockholders’ equity	21,788,546	34,540,346
Total liabilities and stockholders’ equity	$ 82,323,840	$ 39,727,268

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	26,118,722	19,877,857
Common stock, shares outstanding	26,118,722	19,845,611
Common stock, shares subject to repurchase		32,246

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Collaboration revenue	$ 799,046
Total revenues	799,046
Operating expenses:
Research and development	20,293,632	$ 16,297,617	$ 14,908,843
General and administrative	10,337,182	7,833,085	7,379,339
Total operating expenses	30,630,814	24,130,702	22,288,182
Loss from operations	(29,831,768)	(24,130,702)	(22,288,182)
Other income (expense):
Interest income	138,413	67,885	57,616
Interest expense	(70,000)	(70,000)	(70,000)
Other income (expense)	29,914	(15,809)	(19,325)
Total other income (expense)	98,327	(17,924)	(31,709)
Net loss	(29,733,441)	(24,148,626)	(22,319,891)
Other comprehensive income (loss):
Net unrealized (losses) gains on marketable securities	(2,238)	9,390	(24,794)
Comprehensive loss	$ (29,735,679)	$ (24,139,236)	$ (22,344,685)
Net loss per share, basic and diluted	$ (1.31)	$ (1.30)	$ (1.44)
Weighted average shares outstanding used in computing net loss per share, basic and diluted	22,649,911	18,617,537	15,478,999

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2013	$ 53,118,950	$ 1,539	$ 127,536,408	$ 11,497	$ (74,430,494)
Beginning balance, shares at Dec. 31, 2013		15,386,542
Vesting of early exercise of employee stock options	20,602	$ 10	20,592
Vesting of early exercise of employee stock options, shares		93,016
Issuance of common stock upon exercise of stock options	$ 88,422	$ 7	88,415
Issuance of common stock upon exercise of stock options, shares	81,056	81,056
Share-based compensation	$ 2,330,660		2,330,660
Net loss	(22,319,891)				(22,319,891)
Unrealized gain (loss) on marketable securities	(24,794)			(24,794)
Ending balance at Dec. 31, 2014	33,213,949	$ 1,556	129,976,075	(13,297)	(96,750,385)
Ending balance, shares at Dec. 31, 2014		15,560,614
Vesting of early exercise of employee stock options	24,404	$ 9	24,395
Vesting of early exercise of employee stock options, shares		71,249
Issuance of common stock upon exercise of stock options	$ 19,212		19,212
Issuance of common stock upon exercise of stock options, shares	21,029	21,029
Issuance of common stock for employee stock purchase plan	$ 65,523	$ 2	65,521
Issuance of common stock for employee stock purchase plan, shares		17,914
Share-based compensation	3,315,943		3,315,943
Issuance of common stock, net of offering costs	22,040,551	$ 417	22,040,134
Issuance of common stock, net of offering costs, shares		4,174,805
Net loss	(24,148,626)				(24,148,626)
Unrealized gain (loss) on marketable securities	9,390			9,390
Ending balance at Dec. 31, 2015	34,540,346	$ 1,984	155,441,280	(3,907)	(120,899,011)
Ending balance, shares at Dec. 31, 2015		19,845,611
Vesting of early exercise of employee stock options	2,902	$ 3	2,899
Vesting of early exercise of employee stock options, shares		29,707
Issuance of common stock upon exercise of stock options	$ 55,929	$ 6	55,923
Issuance of common stock upon exercise of stock options, shares	60,807	60,807
Issuance of common stock for employee stock purchase plan	$ 49,679	$ 3	49,676
Issuance of common stock for employee stock purchase plan, shares		26,876
Share-based compensation	3,353,456		3,353,456
Issuance of common stock, net of offering costs	13,521,913	$ 616	13,521,297
Issuance of common stock, net of offering costs, shares		6,155,721
Net loss	(29,733,441)				(29,733,441)
Unrealized gain (loss) on marketable securities	(2,238)			(2,238)
Ending balance at Dec. 31, 2016	$ 21,788,546	$ 2,612	$ 172,424,531	$ (6,145)	$ (150,632,452)
Ending balance, shares at Dec. 31, 2016		26,118,722

Statements of Cash Flows

Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (29,733,441)	$ (24,148,626)	$ (22,319,891)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	105,841	67,856	38,258
Stock-based compensation expense	3,353,456	3,315,943	2,330,660
Amortization of premium on marketable securities	5,716	328,479	577,158
Changes in operating assets and liabilities:
Other receivables	(2,500,000)
Prepaid and other current assets	934,991	(1,185,213)	(251,314)
Other assets	(624,101)	(798,754)	(62,981)
Accounts payable and accrued expenses	2,856,020	(581,218)	1,499,601
Accrued compensation	917,801	289,587	(130,345)
Deferred revenue	51,700,954
Deferred rent	(20,236)	165,761	58,699
Net cash provided by (used in) operating activities	26,997,001	(22,546,185)	(18,260,155)
Investing activities
Maturities of marketable securities	44,597,000	62,574,000	54,072,000
Purchase of marketable securities	(40,904,650)	(58,365,836)	(29,639,190)
Capital expenditures	(109,553)	(88,524)	(242,681)
Net cash provided by investing activities	3,582,797	4,119,640	24,190,129
Financing activities
Proceeds from issuance of common stock, net of offering costs	13,521,913	22,305,226
Deferred public offering costs			(264,675)
Proceeds from stock issuances under employee stock purchase plan and exercise of stock options	105,608	84,735	88,422
Net cash provided by (used in) financing activities	13,627,521	22,389,961	(176,253)
Net increase in cash and cash equivalents	44,207,319	3,963,416	5,753,721
Cash and cash equivalents at beginning of period	13,876,090	9,912,674	4,158,953
Cash and cash equivalents at end of period	58,083,409	13,876,090	9,912,674
Supplemental disclosure of cash flow information:
Cash paid for interest	$ 70,000	70,000	$ 70,000
Supplemental schedule of noncash investing and financing activities:
Purchases of property and equipment included in accounts payable		$ 87,000

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Conatus Pharmaceuticals Inc. (the Company) was incorporated in the state of Delaware on July 13, 2005. The Company is a biotechnology company focused on the development and commercialization of novel medicines to treat liver disease. As of December 31, 2016, the Company has devoted substantially all of its efforts to product development and has not realized product sales revenues from its planned principal operations. The Company has a limited operating history, and the sales and income potential of the Company’s business and market are unproven. The Company has experienced net losses since its inception and, as of December 31, 2016, had an accumulated deficit of $150.6 million. The Company expects to continue to incur net losses for at least the next several years. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. If the Company is unable to generate revenues adequate to support its cost structure, the Company may need to raise additional equity or debt financing. As of December 31, 2016, the Company had cash, cash equivalents and marketable securities of $77.0 million and working capital of $40.9 million.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash. Additionally, the Company established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity from the date of purchase of three months or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts. Marketable Securities The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the statements of operations and comprehensive loss and as a separate component of stockholders’ equity. The Company classifies marketable securities with remaining maturities greater than one year as current assets because such marketable securities are available to fund the Company’s current operations. The Company invests its excess cash balances primarily in corporate debt securities and money market funds with strong credit ratings. Realized gains and losses are calculated on the specific identification method and recorded as interest income. There were no realized gains and losses for the years ended December 31, 2016, 2015 and 2014. At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the unrealized loss is other-than-temporary. The Company considers factors including: the significance of the decline in value compared to the cost basis, underlying factors contributing to a decline in the prices of securities in a single asset class, the length of time the market value of the security has been less than its cost basis, the security’s relative performance versus its peers, sector or asset class, expected market volatility and the market and economy in general. When the Company determines that a decline in the fair value below its cost basis is other-than-temporary, the Company recognizes an impairment loss in the period in which the other-than-temporary decline occurred. There have been no other-than-temporary declines in the value of marketable securities for the years ended December 31, 2016, 2015 and 2014, as it is more likely than not the Company will hold the securities until maturity or a recovery of the cost basis. Fair Value of Financial Instruments The carrying amounts of prepaid and other current assets, accounts payable and accrued expenses are reasonable estimates of their fair value because of the short maturity of these items. Property and Equipment Property and equipment, which consists of furniture and fixtures, computers and office equipment and leasehold improvements, are stated at cost and depreciated over the estimated useful lives of the assets (three to five years) using the straight-line method. Leasehold improvements are amortized over the shorter of their estimated useful lives or the lease term. Long-Lived Assets The Company regularly reviews the carrying value and estimated lives of all of its long-lived assets, including property and equipment, to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods, as well as the strategic significance of the assets to the Company’s business objective. Should an impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset’s fair value. The Company has not recognized any impairment losses through December 31, 2016. Revenue Recognition The Company recognizes revenue when each of the following four criteria is met: (i) persuasive evidence of an arrangement exists; (ii) products are delivered or as services are rendered; (iii) the sales price is fixed or determinable; and (iv) collectability is reasonably assured. The Company recognizes revenue under its Option, Collaboration and License Agreement (the Collaboration Agreement) with Novartis Pharma AG (Novartis) based on the relevant accounting literature. Under this guidance, multiple elements or deliverables may include (i) grants of licenses, or options to obtain licenses, to intellectual property, (ii) research and development services, (iii) participation on joint research and/or joint development committees, and/or (iv) manufacturing or supply services. The payments entities may receive under these arrangements typically include one or more of the following: non-refundable, upfront license fees; option exercise fees; funding of research and/or development efforts; amounts due upon the achievement of specified objectives; and/or royalties on future product sales. Multiple-element arrangements require the separability of deliverables included in an arrangement into different units of accounting and the allocation of arrangement consideration to the units of accounting. The evaluation of multiple-element arrangements requires management to make judgments about (i) the identification of deliverables, (ii) whether such deliverables are separable from the other aspects of the contractual relationship, (iii) the estimated selling price of each deliverable, and (iv) the expected period of performance for each deliverable. To determine the units of accounting under a multiple-element arrangement, management evaluates certain separation criteria, including whether the deliverables have stand-alone value, based on the relevant facts and circumstances for each arrangement. Management then estimates the selling price for each unit of accounting and allocates the arrangement consideration to each unit using the relative selling price method. The allocated consideration for each unit of accounting is recognized based on the method most appropriate for that unit of account and in accordance with the revenue recognition criteria detailed above. If there are deliverables in an arrangement that are not separable from other aspects of the contractual relationship, they are treated as a combined unit of accounting, with the allocated revenue for the combined unit recognized in a manner consistent with the revenue recognition applicable to the final deliverable in the combined unit. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets and recognized as revenue when the related revenue recognition criteria are met. The Collaboration Agreement provides for non-refundable milestone payments. The Company recognizes revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to the Company for such milestone (i) is consistent with the Company’s performance necessary to achieve the milestone or the increase in value to the collaboration resulting from the Company’s performance, (ii) relates solely to the Company’s past performance and (iii) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, the Company considers all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. The Company will periodically review the estimated performance periods under the Collaboration Agreement, which provides for non-refundable upfront payments and fees. The Company will adjust the periods over which revenue should be recognized when appropriate to reflect changes in assumptions relating to the estimated performance periods. The Company could accelerate revenue recognition in the event of early termination of programs or if the Company’s expectations change. Alternatively, the Company could decelerate revenue recognition if programs are extended or delayed. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in future periods could be materially impacted. The Company records revenues related to the reimbursement of costs incurred under the Collaboration Agreement where the Company acts as a principal, controls the research and development activities and bears credit risk. Under the Collaboration Agreement, the Company is reimbursed for associated out-of-pocket costs and for a certain amount of the Company’s full-time equivalent (FTE) costs based on an agreed-upon FTE rate. The gross amount of these pass-through reimbursed costs are reported as revenue in the accompanying statements of operations and comprehensive loss, while the actual expenses for which the Company is reimbursed are reflected as research and development costs. See Note 9 – Collaboration and License Agreements for further information. Research and Development Expenses All research and development costs are expensed as incurred. Income Taxes The Company’s policy related to accounting for uncertainty in income taxes prescribes a recognition threshold and measurement attribute criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. As of December 31, 2016, there are no unrecognized tax benefits included in the balance sheet that would, if recognized, affect the Company’s effective tax rate. The Company has not recognized interest and penalties in the balance sheets or statements of operations and comprehensive loss. The Company is subject to U.S. and California taxation. As of December 31, 2016, the Company’s tax years beginning 2005 to date are subject to examination by taxing authorities. Stock-Based Compensation Stock-based compensation expense for stock option grants under the Company’s stock option plans is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the requisite service period of the stock-based award. The fair value is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method described in the Securities and Exchange Commission (SEC) Staff Accounting Bulletin No. 107. The expected volatility of stock options is based upon the historical volatility of a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2016 2015 2014 Assumptions Risk-free interest rate 1.15% - 1.55% 1.54% - 1.94% 1.69% - 2.10% Expected dividend yield 0% 0% 0% Expected volatility 84% 72% - 89% 78% - 105% Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1 Stock-based compensation expense for employee stock purchases under the Company’s 2013 Employee Stock Purchase Plan (the ESPP) is recorded at the estimated fair value of the purchase as of the plan enrollment date and is recognized as expense on a straight-line basis over the applicable six-month ESPP offering period. The fair value is estimated using the Black-Scholes model with inputs that include the applicable risk-free interest rate, expected dividend yield, expected volatility and expected term. Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from nonowner sources, including unrealized gains and losses on marketable securities. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss for all periods presented. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is used in making decisions regarding resource allocation and assessing performance. To date, the Company has viewed its operations and managed its business as one segment operating primarily in the United States. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and common share equivalents outstanding for the period. Common stock equivalents are only included when their effect is dilutive. The Company’s potentially dilutive securities, which include warrants to purchase common stock, outstanding stock options under the Company’s stock option plans, common stock subject to repurchase by the Company and potential shares to be purchased under the ESPP, have been excluded from the computation of diluted net loss per share in the periods in which they would be anti-dilutive. For all periods presented, there is no difference in the number of shares used to compute basic and diluted shares outstanding due to the Company’s net loss position. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive. December 31, 2016 2015 2014 Warrants to purchase common stock 149,704 149,704 149,704 Common stock options issued and outstanding 3,393,813 2,464,849 1,859,034 Common stock subject to repurchase — 32,246 135,220 ESPP shares pending issuance 2,659 5,103 2,175 Total 3,546,176 2,651,902 2,146,133 Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606). In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. In November 2015, the FASB issued ASU No. 2015-17, Balance Sheet Classification of Deferred Taxes. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718). In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Includes financial instruments for which quoted market prices for identical instruments are available in active markets. Level 2: Includes financial instruments for which there are inputs other than quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transaction (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. Level 3: Includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions. Below is a summary of assets measured at fair value as of December 31, 2016 and 2015. Fair Value Measurements Using December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds $ 45,523,208 $ 45,523,208 $ — $ — Corporate debt securities 27,702,317 — 27,702,317 — Total $ 73,225,525 $ 45,523,208 $ 27,702,317 $ — Fair Value Measurements Using December 31, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds $ 10,221,563 $ 10,221,563 $ — $ — Corporate debt securities 24,334,917 — 24,334,917 — Total $ 34,556,480 $ 10,221,563 $ 24,334,917 $ — The Company’s marketable securities, consisting principally of debt securities, are classified as available-for-sale, are stated at fair value, and consist of Level 2 financial instruments in the fair value hierarchy. The Company determines the fair value of its debt security holdings based on pricing from a service provider. The service provider values the securities based on using market prices from a variety of industry-standard independent data providers. Such market prices may be quoted prices in active markets for identical assets (Level 1 inputs) or pricing determined using inputs other than quoted prices that are observable either directly or indirectly (Level 2 inputs), such as yield curve, volatility factors, credit spreads, default rates, loss severity, current market and contractual prices for the underlying instruments or debt, broker and dealer quotes, as well as other relevant economic measures.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities The Company invests its excess cash in money market funds and debt instruments of financial institutions, corporations, government sponsored entities and municipalities. The following tables summarize the Company’s marketable securities: As of December 31, 2016 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 18,937,860 $ 901 $ (7,046 ) $ 18,931,715 Total $ 18,937,860 $ 901 $ (7,046 ) $ 18,931,715 As of December 31, 2015 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 22,635,926 $ 6,770 $ (10,677 ) $ 22,632,019 Total $ 22,635,926 $ 6,770 $ (10,677 ) $ 22,632,019

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment consist of the following: December 31, 2016 2015 Furniture and fixtures $ 333,670 $ 326,788 Computer equipment and office equipment 119,354 170,946 Leasehold improvements 152,217 142,032 605,241 639,766 Less accumulated depreciation and amortization (343,795 ) (295,032 ) Total $ 261,446 $ 344,734 Depreciation expense related to property and equipment was $105,841, $67,856 and $38,258 for the years ended December 31, 2016, 2015 and 2014, respectively.

Notes Payable

Notes Payable	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Notes Payable	6. Notes Payable In July 2010, the Company entered into a $1.0 million promissory note payable to Pfizer Inc. (Pfizer). The note bears interest at 7% per annum, which is paid quarterly, and matures on July 29, 2020. The note payable prohibits the Company from paying cash dividends and is subject to acceleration upon specified events of default as defined in the agreement including the failure to notify Pfizer of certain material adverse events. In July 2013, the note payable to Pfizer was amended to become convertible into shares of the Company’s common stock following the completion of the Company’s initial public offering (IPO), at the option of the holder, at a price per share equal to the fair market value of the common stock on the date of conversion. The Company’s promissory note payable to Pfizer is recorded on the balance sheet at face value. Based on borrowing rates currently available to the Company for loans with similar terms, the Company believes that the fair value of the Pfizer note approximates its carrying value. The fair value measurement is categorized within Level 3 of the fair value hierarchy. Previously, the Pfizer note was classified as a long-term liability, but was reclassified as a current liability in December 2016 to reflect the Company’s prepayment of the principal balance and accrued interest in January 2017.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity Common Stock In August 2014, the Company entered into an At Market Issuance Sales Agreement (the Sales Agreement) with MLV & Co. LLC (MLV), pursuant to which the Company may sell from time to time, at its option, up to an aggregate of $50.0 million of shares of its common stock through MLV, as sales agent. Sales of the Company’s common stock made pursuant to the Sales Agreement are made on The NASDAQ Global Market (Nasdaq) under the Company’s Registration Statement on Form S-3, filed with the SEC on August 14, 2014 and declared effective by the SEC on August 25, 2014, by means of ordinary brokers’ transactions at market prices. The Company agreed to pay a commission rate equal to up to 3% of the gross sales price per share sold. The Company also agreed to provide MLV with customary indemnification and contribution rights. During the year ended December 31, 2016, the Company sold 6,155,721 shares of its common stock pursuant to the Sales Agreement at a weighted average price per share of $2.26 and received net proceeds of $13.5 million, after deducting offering-related transaction costs and commissions. During the year ended December 31, 2015, the Company sold 149,805 shares of its common stock pursuant to the Sales Agreement at a weighted average price per share of $6.05 and received net proceeds of $0.6 million, after deducting offering-related transaction costs and commissions. The Company terminated the Sales Agreement in December 2016. In April 2015, the Company completed a public offering of 4,025,000 shares of its common stock at a public offering price of $5.75 per share. The shares were registered pursuant to the Registration Statement on Form S-3 filed on August 14, 2014. The Company received net proceeds of $21.4 million, after deducting underwriting discounts and commissions and offering-related transaction costs. Warrants In 2013, the Company issued warrants exercisable for 1,124,026 shares of Series B preferred stock, at an exercise price of $0.90 per share, to certain existing investors in conjunction with a private placement (the 2013 Warrants) and warrants exercisable for 111,112 shares of Series B preferred stock, at an exercise price of $0.90 per share, to Oxford Finance LLC and Silicon Valley Bank in conjunction with the Company’s entry into a loan and security agreement (the Lender Warrants). Upon completion of the IPO, the 2013 Warrants and the Lender Warrants became exercisable for 136,236 and 13,468 shares of common stock, respectively, at an exercise price of $7.43 per share. The 2013 Warrants and the Lender Warrants will expire on May 30, 2018 and July 3, 2023, respectively. Stock Options The Company adopted an Equity Incentive Plan in 2006 (the 2006 Plan) under which 1,030,303 shares of common stock were reserved for issuance to employees, nonemployee directors and consultants of the Company. In July 2013, the Company adopted an Incentive Award Plan (the 2013 Plan), which provides for the grant of incentive stock options, nonstatutory stock options, rights to purchase restricted stock, stock appreciation rights, dividend equivalents, stock payments and restricted stock units to eligible recipients. Recipients of incentive stock options shall be eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair market value of such stock on the date of grant. The maximum term of options granted under the 2013 Plan is ten years. Except for annual grants to non-employee directors, which vest one year from the grant date, options generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years. Pursuant to the 2013 Plan, the Company’s management is authorized to grant stock options to the Company’s employees, directors and consultants. The number of shares available for future grant under the 2013 Plan will automatically increase each year by an amount equal to the least of (1) 1,000,000 shares of the Company’s common stock, (2) 5% of the outstanding shares of the Company’s common stock as of the last day of the Company’s immediately preceding fiscal year, or (3) such other amount as the Company’s board of directors may determine. Shares that remain available, that expire or otherwise terminate without having been exercised in full, and unvested shares that are forfeited to or repurchased by the Company under the 2006 Plan will roll into the 2013 Plan. As of December 31, 2016, a total of 600,191 options remain available for future grant under the 2013 Plan. The following table summarizes the Company’s stock option activity under all stock option plans for the three years ended December 31, 2016. Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Outstanding at December 31, 2013 790,590 $ 4.01 Granted 1,212,000 8.41 Exercised (81,056 ) 1.10 Cancelled (62,500 ) 9.09 Outstanding at December 31, 2014 1,859,034 6.84 Granted 822,250 6.03 Exercised (21,029 ) 1.04 Cancelled (195,406 ) 7.79 Outstanding at December 31, 2015 2,464,849 6.54 Granted 1,132,500 1.96 Exercised (60,807 ) 0.92 Cancelled (142,729 ) 6.65 Outstanding at December 31, 2016 3,393,813 $ 5.10 7.65 Vested or expected to vest at December 31, 2016 3,139,848 $ 5.36 7.58 Exercisable at December 31, 2016 1,781,525 $ 6.03 6.78 The weighted-average fair value of options granted for the years ended December 31, 2016, 2015 and 2014 were $1.38, $4.31 and $6.77, respectively. The total intrinsic value of stock options exercised during the years ended December 31, 2016, 2015 and 2014 were $0.1 million, $0.1 million and $0.5 million, respectively. At December 31, 2016, the intrinsic value of options outstanding, vested or expected to vest, and exercisable were $5.3 million, $4.5 million and $2.1 million, respectively. Employee Stock Purchase Plan In July 2013, the Company adopted the ESPP, which permits participants to contribute up to 20% of their eligible compensation during defined rolling six-month periods to purchase the Company’s common stock. The purchase price of the shares will be 85% of the lower of the fair market value of the Company’s common stock on the first day of trading of the offering period or on the applicable purchase date. The ESPP was activated in November 2014. The Company issued 26,876, 17,914 and 0 shares of common stock under the ESPP for the years ended December 31, 2016, 2015 and 2014, respectively. The Company had an outstanding liability of $4,521, $15,789 and $13,167 at December 31, 2016, 2015 and 2014, respectively, which is included in accounts payable and accrued expenses on the balance sheets, for employee contributions to the ESPP for shares pending issuance at the end of the offering period. Stock-Based Compensation The Company recorded stock-based compensation of $3.4 million, $3.3 million and $2.3 million for the years ended December 31, 2016, 2015 and 2014, respectively. Unrecognized compensation expense at December 31, 2016 was $4.4 million, which is expected to be recognized over a weighted-average vesting term of 1.8 years. Common Stock Reserved for Future Issuance The following shares of common stock were reserved for future issuance at December 31, 2016 and 2015: December 31, 2016 2015 Warrants to purchase common stock 149,704 149,704 Common stock options issued and outstanding 3,393,813 2,464,849 Common stock authorized for future option grants 600,191 593,531 Common stock authorized for the ESPP 555,210 432,086 Total 4,698,918 3,640,170

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by the federal and state jurisdictions where applicable. There are currently no pending income tax examinations. The Company’s tax years for 2005 and forward are subject to examination by the federal and California tax authorities due to the carryforward of unutilized net operating losses and research and development credits. Pursuant to Internal Revenue Code (IRC) Sections 382 and 383, annual use of the Company’s net operating loss and research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period. The Company is currently in the process of completing an IRC Section 382/383 analysis regarding the limitation of net operating loss and research and development credit carryforwards. Due to the existence of the valuation allowance, future changes in the Company’s unrecognized tax benefits will not impact the Company’s effective tax rate. Significant components of the Company’s deferred tax assets at December 31, 2016 and 2015 are shown below: December 31, 2016 2015 Deferred tax assets Net operating loss carryovers $ 41,103,000 $ 33,007,000 Research and development tax credits 4,989,000 3,585,000 Intangibles 643,000 922,000 Stock options 2,071,000 1,614,000 Compensation 786,000 553,000 Other 486,000 212,000 Total gross deferred tax assets 50,078,000 39,893,000 Less valuation allowance (50,078,000 ) (39,893,000 ) Net deferred tax assets $ — $ — A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2016, 2015 and 2014 is as follows: December 31, 2016 2015 2014 Statutory rate 34.00 % 34.00 % 34.00 % State tax, net of federal benefit 0.00 % 5.83 % 5.83 % Valuation allowance (34.26 %) (42.48 )% (39.85 )% Other 0.26 % 2.65 % 0.02 % Effective tax rate — % — % — % At December 31, 2016, the Company has federal and state net operating loss carryforwards of $107.6 million and $80.7 million, respectively. The federal loss carryforwards begin to expire in 2025, unless previously utilized, and the state carryforwards began to expire in 2015. California net operating losses of $2.8 million expired in 2016; $4.2 million will expire in 2017 unless utilized; and the remainder will expire in 2028 and beyond unless previously utilized. The Company also has federal and state research credit carryforwards of $5.0 million and $1.6 million, respectively. The federal research credit carryforwards will begin expiring in 2026, unless previously utilized. The state research credit will carry forward indefinitely. The change in the valuation allowance is an increase of $10.2 million, $10.3 million and $8.9 million for the years ended December 31, 2016, 2015 and 2014, respectively. The Company accounts for income taxes in accordance with Accounting Standards Codification 740-10, Accounting for Uncertainty in Income Tax. The impact of an uncertain income tax position is recognized at the largest amount that is “more likely than not” to be sustained upon audit by the relevant taxing authority. An uncertain tax position will not be recognized if it has less than a 50% likelihood of being sustained. The following table summarizes the activity related to the Company’s unrecognized tax benefits: 2016 2015 2014 Balance at beginning of year $ 981,380 $ 571,194 $ 457,106 Additions based on tax positions related to the current year 337,459 337,862 141,866 Additions for tax positions of prior years — 72,324 — Reductions for tax positions of prior years — — (27,778 ) Balance at end of year $ 1,318,839 $ 981,380 $ 571,194 The Company does not expect that the unrecognized tax benefits will change within 12 months of this reporting date. Due to the existence of the valuation allowance, future changes in the Company’s unrecognized tax benefits will not impact the Company’s effective tax rate. The Company’s policy is to recognize interest and penalties related to income tax matters in income tax expense. For the years ended December 31, 2016, 2015 and 2014, the Company has not recognized any interest or penalties related to income taxes.

Collaboration and License Agree

Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration and License Agreements	9. Collaboration and License Agreements In December 2016, the Company entered into the Collaboration Agreement with Novartis, pursuant to which the Company granted Novartis an exclusive option to collaborate with the Company to develop products containing emricasan. Pursuant to the Collaboration Agreement, the Company received a non-refundable upfront payment of $50.0 million from Novartis. Following Novartis’ exercise of the option, the Company will receive $7.0 million, subject to certain usual and customary closing conditions, including required anti-trust approvals, at which time the license under the Collaboration Agreement will become effective. Furthermore, if Novartis exercises its option under the Collaboration Agreement, the Company will be eligible to receive up to an aggregate of $650.0 million in milestone payments over the term of the Collaboration Agreement, contingent on the achievement of certain development, regulatory and commercial milestones. Under the Collaboration Agreement, the Company is responsible for completing its Phase 2b trials. Novartis will generally pay 50% of the Company’s Phase 2b emricasan development costs after the license grant is effective. Novartis will assume full responsibility for emricasan’s Phase 3 development and all combination product development. If Novartis does not exercise the option during the designated option period, the Collaboration Agreement will expire. If Novartis exercises the option, unless terminated earlier, the Collaboration Agreement will remain in effect on a product-by-product and country-by-country basis until Novartis’ royalty obligations expire. Novartis has certain termination rights in the event of a mandated clinical trial hold for any product containing emricasan as its sole active ingredient. Additionally, after the license effective date, Novartis has the right to terminate the Collaboration Agreement without cause upon 180 days prior written notice to the Company. In such event, the license granted to Novartis will be terminated and revert to the Company. In the event Novartis terminates the Collaboration Agreement due to the Company’s uncured material breach or insolvency, the license granted to Novartis pursuant to the Collaboration Agreement will become irrevocable, and Novartis will be required to continue to make all milestone and royalty payments otherwise due to the Company under the Collaboration Agreement, provided that if the Company materially breaches the Collaboration Agreement such that the rights licensed to Novartis or the commercial prospects of the emricasan products are seriously impaired, the milestone and royalty payments will be reduced by 50%. Under the relevant accounting literature, the Collaboration Agreement meets the definition of a collaborative arrangement and a multiple-element arrangement. The Company concluded that there were two significant deliverables under the Collaboration Agreement – the option to obtain the license and the research and development services – but that the license does not have stand-alone value as Novartis cannot obtain value from the license without the research and development services, which the Company is uniquely able to perform. As such, the Company will recognize as collaboration revenue a portion of the upfront payment received of $50.0 million, the option exercise fee of $7.0 million, and the imputed income from the Investment Agreement as described below on a straight-line basis between the inception of the agreement (or upon exercise with respect to the option exercise fee) through mid 2019 – the estimated period over which the Company expects to perform the research and development services. Expense reimbursements for the Company’s Phase 2b emricasan development costs will be recognized as collaboration revenue when the related expenses are incurred. Under the Investment Agreement, the Company is able to borrow up to $15.0 million at a coupon rate of 6%, under one or two notes, which mature on December 31, 2019. The Company may elect at its sole discretion to convert all or part of the outstanding principal and accrued interest into fully paid and non-assessable shares of common stock, at 120% of the 20-day trailing average closing price per share of the common stock immediately prior to the conversion date. Novartis has the option to convert in the event of a change in control of the Company or termination of the Collaboration Agreement by Novartis pursuant to certain provisions. In the event the one or two notes is converted into shares of the Company’s common stock, Novartis will receive the lesser of 19.0% of the Company’s outstanding shares on a fully-diluted basis (i) at the inception of the Investment Agreement or (ii) on the conversion date, and shall receive cash for any remaining principal and unpaid interest after such conversion. This ability to borrow and repay the debt at a discount using shares of the Company’s common stock was deemed to be additional, foregone revenue attributable to the Collaboration Agreement, which the Company imputed and recorded as both a receivable from Novartis and a liability (deferred revenue) of $2.5 million at the inception of the agreements.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2016
Postemployment Benefits [Abstract]
Employee Benefits	10 . Employee Benefits Effective December 4, 2006, the Company has a defined contribution 401(k) plan for its employees. Employees are eligible to participate in the plan beginning on the first day of employment. Under the terms of the plan, employees may make voluntary contributions as a percent of compensation. Effective January 1, 2007,

Commitments

Commitments	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments	11 . Commitments In February 2014, the Company entered into a noncancelable operating lease agreement (the Lease) for certain office space with a lease term from July 2014 through December 2019 and a renewal option for an additional five years. In May 2015, the Company entered into a first amendment to the Lease (the First Lease Amendment) for additional office space starting in September 2015 through September 2020. The First Lease Amendment also extended the term of the Lease to September 2020. The monthly base rent under the Lease and the First Lease Amendment increases approximately 3% annually from $32,784 in 2015 to $39,268 in 2020. Future minimum payments under this noncancelable operating lease total $1.6 million at December 31, 2016. Rent expense was $378,005, $339,053 and $243,832 for the years ended December 31, 2016, 2015 and 2014, respectively. In July 2010, the Company entered into a stock purchase agreement with Pfizer, pursuant to which the Company acquired all of the outstanding stock of Idun, which was subsequently spun off to the Company’s stockholders in January 2013. Under the stock purchase agreement, the Company may be required to make payments to Pfizer totaling $18.0 million upon the achievement of specified regulatory milestones.

Quarterly Financial Data

Quarterly Financial Data	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	12. Quarterly Financial Data (unaudited) The following tables summarize the unaudited quarterly financial data for the last two fiscal years. 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ — $ — $ — $ 799,046 Total operating expenses 7,274,589 6,484,622 6,894,868 9,976,735 Total other income 2,705 13,477 27,958 54,187 Net loss (7,271,884 ) (6,471,145 ) (6,866,910 ) (9,123,502 ) Net loss per share, basic and diluted (1) (0.35 ) (0.30 ) (0.31 ) (0.35 ) 2015 First Quarter Second Quarter Third Quarter Fourth Quarter Total operating expenses $ 5,964,922 $ 6,064,479 $ 6,061,335 $ 6,039,966 Total other (expense) income (14,742 ) 7,225 (6,211 ) (4,196 ) Net loss (5,979,664 ) (6,057,254 ) (6,067,546 ) (6,044,162 ) Net loss per share, basic and diluted (1) (0.38 ) (0.31 ) (0.31 ) (0.30 ) (1)

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Events	13 . Subsequent Events On January 24, 2017, the Company voluntarily prepaid the Promissory Note, dated July 29, 2010, as amended on July 3, 2013, by and between the Company and Pfizer Inc. (the Promissory Note). The Promissory Note bore interest at a per annum interest rate equal to 7%, compounded quarterly, and was scheduled to mature on July 29, 2020. Interest was payable on a quarterly basis during the term of the Promissory Note. The Company prepaid the entire balance of the outstanding principal and accrued and unpaid interest of the Promissory Note in the amount of $1,004,861. On February 15, 2017, the Company issued a convertible promissory note (the Note) in the principal amount of $15.0 million. The Note was issued pursuant to the Investment Agreement entered into between the Company and Novartis on December 19, 2016. The maturity date of the Note is December 31, 2019. The Note bears interest on the unpaid principal amount at a rate of 6% per annum. The Company may prepay or convert the Note into shares of the Company’s common stock, at its option, until December 31, 2019. Novartis may convert the Note into shares of the Company’s common stock upon a change of control of the Company or termination of the Collaboration Agreement entered into between the parties in its entirety. If converted, the principal and accrued interest under the Note will convert into the Company’s common stock at a conversion price equal to 120% of the 20-day trailing average closing price per share of the common stock immediately prior to the conversion date. Upon the occurrence of certain events of default, the Note requires the Company to repay the principal amount of the Note and any unpaid accrued interest.

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash. Additionally, the Company established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity from the date of purchase of three months or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts.
Marketable Securities	Marketable Securities The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the statements of operations and comprehensive loss and as a separate component of stockholders’ equity. The Company classifies marketable securities with remaining maturities greater than one year as current assets because such marketable securities are available to fund the Company’s current operations. The Company invests its excess cash balances primarily in corporate debt securities and money market funds with strong credit ratings. Realized gains and losses are calculated on the specific identification method and recorded as interest income. There were no realized gains and losses for the years ended December 31, 2016, 2015 and 2014. At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the unrealized loss is other-than-temporary. The Company considers factors including: the significance of the decline in value compared to the cost basis, underlying factors contributing to a decline in the prices of securities in a single asset class, the length of time the market value of the security has been less than its cost basis, the security’s relative performance versus its peers, sector or asset class, expected market volatility and the market and economy in general. When the Company determines that a decline in the fair value below its cost basis is other-than-temporary, the Company recognizes an impairment loss in the period in which the other-than-temporary decline occurred. There have been no other-than-temporary declines in the value of marketable securities for the years ended December 31, 2016, 2015 and 2014, as it is more likely than not the Company will hold the securities until maturity or a recovery of the cost basis.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of prepaid and other current assets, accounts payable and accrued expenses are reasonable estimates of their fair value because of the short maturity of these items.
Property and Equipment	Property and Equipment Property and equipment, which consists of furniture and fixtures, computers and office equipment and leasehold improvements, are stated at cost and depreciated over the estimated useful lives of the assets (three to five years) using the straight-line method. Leasehold improvements are amortized over the shorter of their estimated useful lives or the lease term.
Long-Lived Assets	Long-Lived Assets The Company regularly reviews the carrying value and estimated lives of all of its long-lived assets, including property and equipment, to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods, as well as the strategic significance of the assets to the Company’s business objective. Should an impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset’s fair value. The Company has not recognized any impairment losses through December 31, 2016.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when each of the following four criteria is met: (i) persuasive evidence of an arrangement exists; (ii) products are delivered or as services are rendered; (iii) the sales price is fixed or determinable; and (iv) collectability is reasonably assured. The Company recognizes revenue under its Option, Collaboration and License Agreement (the Collaboration Agreement) with Novartis Pharma AG (Novartis) based on the relevant accounting literature. Under this guidance, multiple elements or deliverables may include (i) grants of licenses, or options to obtain licenses, to intellectual property, (ii) research and development services, (iii) participation on joint research and/or joint development committees, and/or (iv) manufacturing or supply services. The payments entities may receive under these arrangements typically include one or more of the following: non-refundable, upfront license fees; option exercise fees; funding of research and/or development efforts; amounts due upon the achievement of specified objectives; and/or royalties on future product sales. Multiple-element arrangements require the separability of deliverables included in an arrangement into different units of accounting and the allocation of arrangement consideration to the units of accounting. The evaluation of multiple-element arrangements requires management to make judgments about (i) the identification of deliverables, (ii) whether such deliverables are separable from the other aspects of the contractual relationship, (iii) the estimated selling price of each deliverable, and (iv) the expected period of performance for each deliverable. To determine the units of accounting under a multiple-element arrangement, management evaluates certain separation criteria, including whether the deliverables have stand-alone value, based on the relevant facts and circumstances for each arrangement. Management then estimates the selling price for each unit of accounting and allocates the arrangement consideration to each unit using the relative selling price method. The allocated consideration for each unit of accounting is recognized based on the method most appropriate for that unit of account and in accordance with the revenue recognition criteria detailed above. If there are deliverables in an arrangement that are not separable from other aspects of the contractual relationship, they are treated as a combined unit of accounting, with the allocated revenue for the combined unit recognized in a manner consistent with the revenue recognition applicable to the final deliverable in the combined unit. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets and recognized as revenue when the related revenue recognition criteria are met. The Collaboration Agreement provides for non-refundable milestone payments. The Company recognizes revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to the Company for such milestone (i) is consistent with the Company’s performance necessary to achieve the milestone or the increase in value to the collaboration resulting from the Company’s performance, (ii) relates solely to the Company’s past performance and (iii) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, the Company considers all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. The Company will periodically review the estimated performance periods under the Collaboration Agreement, which provides for non-refundable upfront payments and fees. The Company will adjust the periods over which revenue should be recognized when appropriate to reflect changes in assumptions relating to the estimated performance periods. The Company could accelerate revenue recognition in the event of early termination of programs or if the Company’s expectations change. Alternatively, the Company could decelerate revenue recognition if programs are extended or delayed. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in future periods could be materially impacted. The Company records revenues related to the reimbursement of costs incurred under the Collaboration Agreement where the Company acts as a principal, controls the research and development activities and bears credit risk. Under the Collaboration Agreement, the Company is reimbursed for associated out-of-pocket costs and for a certain amount of the Company’s full-time equivalent (FTE) costs based on an agreed-upon FTE rate. The gross amount of these pass-through reimbursed costs are reported as revenue in the accompanying statements of operations and comprehensive loss, while the actual expenses for which the Company is reimbursed are reflected as research and development costs. See Note 9 – Collaboration and License Agreements for further information.
Research and Development Expenses	Research and Development Expenses All research and development costs are expensed as incurred.
Income Taxes	Income Taxes The Company’s policy related to accounting for uncertainty in income taxes prescribes a recognition threshold and measurement attribute criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. As of December 31, 2016, there are no unrecognized tax benefits included in the balance sheet that would, if recognized, affect the Company’s effective tax rate. The Company has not recognized interest and penalties in the balance sheets or statements of operations and comprehensive loss. The Company is subject to U.S. and California taxation. As of December 31, 2016, the Company’s tax years beginning 2005 to date are subject to examination by taxing authorities.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense for stock option grants under the Company’s stock option plans is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the requisite service period of the stock-based award. The fair value is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method described in the Securities and Exchange Commission (SEC) Staff Accounting Bulletin No. 107. The expected volatility of stock options is based upon the historical volatility of a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2016 2015 2014 Assumptions Risk-free interest rate 1.15% - 1.55% 1.54% - 1.94% 1.69% - 2.10% Expected dividend yield 0% 0% 0% Expected volatility 84% 72% - 89% 78% - 105% Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1 Stock-based compensation expense for employee stock purchases under the Company’s 2013 Employee Stock Purchase Plan (the ESPP) is recorded at the estimated fair value of the purchase as of the plan enrollment date and is recognized as expense on a straight-line basis over the applicable six-month ESPP offering period. The fair value is estimated using the Black-Scholes model with inputs that include the applicable risk-free interest rate, expected dividend yield, expected volatility and expected term.
Comprehensive Loss	Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from nonowner sources, including unrealized gains and losses on marketable securities. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss for all periods presented.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is used in making decisions regarding resource allocation and assessing performance. To date, the Company has viewed its operations and managed its business as one segment operating primarily in the United States.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and common share equivalents outstanding for the period. Common stock equivalents are only included when their effect is dilutive. The Company’s potentially dilutive securities, which include warrants to purchase common stock, outstanding stock options under the Company’s stock option plans, common stock subject to repurchase by the Company and potential shares to be purchased under the ESPP, have been excluded from the computation of diluted net loss per share in the periods in which they would be anti-dilutive. For all periods presented, there is no difference in the number of shares used to compute basic and diluted shares outstanding due to the Company’s net loss position. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive. December 31, 2016 2015 2014 Warrants to purchase common stock 149,704 149,704 149,704 Common stock options issued and outstanding 3,393,813 2,464,849 1,859,034 Common stock subject to repurchase — 32,246 135,220 ESPP shares pending issuance 2,659 5,103 2,175 Total 3,546,176 2,651,902 2,146,133
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606). In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. In November 2015, the FASB issued ASU No. 2015-17, Balance Sheet Classification of Deferred Taxes. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718). In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Schedule of Black-Scholes Option Pricing Model Assumptions	The fair value is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method described in the Securities and Exchange Commission (SEC) Staff Accounting Bulletin No. 107. The expected volatility of stock options is based upon the historical volatility of a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2016 2015 2014 Assumptions Risk-free interest rate 1.15% - 1.55% 1.54% - 1.94% 1.69% - 2.10% Expected dividend yield 0% 0% 0% Expected volatility 84% 72% - 89% 78% - 105% Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1
Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share	The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive. December 31, 2016 2015 2014 Warrants to purchase common stock 149,704 149,704 149,704 Common stock options issued and outstanding 3,393,813 2,464,849 1,859,034 Common stock subject to repurchase — 32,246 135,220 ESPP shares pending issuance 2,659 5,103 2,175 Total 3,546,176 2,651,902 2,146,133

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value	Below is a summary of assets measured at fair value as of December 31, 2016 and 2015. Fair Value Measurements Using December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds $ 45,523,208 $ 45,523,208 $ — $ — Corporate debt securities 27,702,317 — 27,702,317 — Total $ 73,225,525 $ 45,523,208 $ 27,702,317 $ — Fair Value Measurements Using December 31, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds $ 10,221,563 $ 10,221,563 $ — $ — Corporate debt securities 24,334,917 — 24,334,917 — Total $ 34,556,480 $ 10,221,563 $ 24,334,917 $ —

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Summary of Marketable Securities	The Company invests its excess cash in money market funds and debt instruments of financial institutions, corporations, government sponsored entities and municipalities. The following tables summarize the Company’s marketable securities: As of December 31, 2016 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 18,937,860 $ 901 $ (7,046 ) $ 18,931,715 Total $ 18,937,860 $ 901 $ (7,046 ) $ 18,931,715 As of December 31, 2015 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 22,635,926 $ 6,770 $ (10,677 ) $ 22,632,019 Total $ 22,635,926 $ 6,770 $ (10,677 ) $ 22,632,019

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consist of the following: December 31, 2016 2015 Furniture and fixtures $ 333,670 $ 326,788 Computer equipment and office equipment 119,354 170,946 Leasehold improvements 152,217 142,032 605,241 639,766 Less accumulated depreciation and amortization (343,795 ) (295,032 ) Total $ 261,446 $ 344,734

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity under all stock option plans for the three years ended December 31, 2016. Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Outstanding at December 31, 2013 790,590 $ 4.01 Granted 1,212,000 8.41 Exercised (81,056 ) 1.10 Cancelled (62,500 ) 9.09 Outstanding at December 31, 2014 1,859,034 6.84 Granted 822,250 6.03 Exercised (21,029 ) 1.04 Cancelled (195,406 ) 7.79 Outstanding at December 31, 2015 2,464,849 6.54 Granted 1,132,500 1.96 Exercised (60,807 ) 0.92 Cancelled (142,729 ) 6.65 Outstanding at December 31, 2016 3,393,813 $ 5.10 7.65 Vested or expected to vest at December 31, 2016 3,139,848 $ 5.36 7.58 Exercisable at December 31, 2016 1,781,525 $ 6.03 6.78
Summary of Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance at December 31, 2016 and 2015: December 31, 2016 2015 Warrants to purchase common stock 149,704 149,704 Common stock options issued and outstanding 3,393,813 2,464,849 Common stock authorized for future option grants 600,191 593,531 Common stock authorized for the ESPP 555,210 432,086 Total 4,698,918 3,640,170

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Components of Company's Deferred Tax Assets	Significant components of the Company’s deferred tax assets at December 31, 2016 and 2015 are shown below: December 31, 2016 2015 Deferred tax assets Net operating loss carryovers $ 41,103,000 $ 33,007,000 Research and development tax credits 4,989,000 3,585,000 Intangibles 643,000 922,000 Stock options 2,071,000 1,614,000 Compensation 786,000 553,000 Other 486,000 212,000 Total gross deferred tax assets 50,078,000 39,893,000 Less valuation allowance (50,078,000 ) (39,893,000 ) Net deferred tax assets $ — $ —
Reconciliation of Statutory Tax Rates and Effective Tax Rates	A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2016, 2015 and 2014 is as follows: December 31, 2016 2015 2014 Statutory rate 34.00 % 34.00 % 34.00 % State tax, net of federal benefit 0.00 % 5.83 % 5.83 % Valuation allowance (34.26 %) (42.48 )% (39.85 )% Other 0.26 % 2.65 % 0.02 % Effective tax rate — % — % — %
Unrecognized Tax Benefits	The following table summarizes the activity related to the Company’s unrecognized tax benefits: 2016 2015 2014 Balance at beginning of year $ 981,380 $ 571,194 $ 457,106 Additions based on tax positions related to the current year 337,459 337,862 141,866 Additions for tax positions of prior years — 72,324 — Reductions for tax positions of prior years — — (27,778 ) Balance at end of year $ 1,318,839 $ 981,380 $ 571,194

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Data	The following tables summarize the unaudited quarterly financial data for the last two fiscal years. 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ — $ — $ — $ 799,046 Total operating expenses 7,274,589 6,484,622 6,894,868 9,976,735 Total other income 2,705 13,477 27,958 54,187 Net loss (7,271,884 ) (6,471,145 ) (6,866,910 ) (9,123,502 ) Net loss per share, basic and diluted (1) (0.35 ) (0.30 ) (0.31 ) (0.35 ) 2015 First Quarter Second Quarter Third Quarter Fourth Quarter Total operating expenses $ 5,964,922 $ 6,064,479 $ 6,061,335 $ 6,039,966 Total other (expense) income (14,742 ) 7,225 (6,211 ) (4,196 ) Net loss (5,979,664 ) (6,057,254 ) (6,067,546 ) (6,044,162 ) Net loss per share, basic and diluted (1) (0.38 ) (0.31 ) (0.31 ) (0.30 )

Organization and Basis of Pre28

Organization and Basis of Presentation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Date of incorporation	Jul. 13, 2005
Accumulated deficit	$ (150,632,452)	$ (120,899,011)
Cash, cash equivalents and marketable securities	77,000,000
Working capital	$ 40,900,000

Summary of Significant Accoun29

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)Segment	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Property, Plant and Equipment [Line Items]
Realized gains and losses on investments	$ 0	$ 0	$ 0
Other-than-temporary declines in value of marketable securities	0	$ 0	$ 0
Impairment losses not recognized	0
Unrecognized tax benefits that would, if recognized, affect the Company’s effective tax rate	$ 0
Risk-free interest rate basis	The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date.
Number of operating segment | Segment	1
Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of the assets	3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of the assets	5 years

Summary of Significant Accoun30

Summary of Significant Accounting Policies - Schedule of Black-Scholes Option Pricing Model Assumptions (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate - Minimum	1.15%	1.54%	1.69%
Risk-free interest rate - Maximum	1.55%	1.94%	2.10%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	84.00%
Expected volatility - Minimum		72.00%	78.00%
Expected volatility - Maximum		89.00%	105.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months	5 years 6 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	3,546,176	2,651,902	2,146,133
ESPP shares pending issuance [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	2,659	5,103	2,175
Warrants to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	149,704	149,704	149,704
Common stock options issued and outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	3,393,813	2,464,849	1,859,034
Common stock subject to repurchase [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities		32,246	135,220

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets Measured at Fair Value (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 73,225,525	$ 34,556,480
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	45,523,208	10,221,563
Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	27,702,317	24,334,917
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	45,523,208	10,221,563
Level 1 [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	45,523,208	10,221,563
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	27,702,317	24,334,917
Level 2 [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 27,702,317	$ 24,334,917

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 18,937,860	$ 22,635,926
Unrealized Gains	901	6,770
Unrealized Losses	(7,046)	(10,677)
Estimated Fair Value	18,931,715	22,632,019
Corporate debt securities 1 or less years of maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,937,860	22,635,926
Unrealized Gains	901	6,770
Unrealized Losses	(7,046)	(10,677)
Estimated Fair Value	$ 18,931,715	$ 22,632,019

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 605,241	$ 639,766
Less accumulated depreciation and amortization	(343,795)	(295,032)
Total	261,446	344,734
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	333,670	326,788
Computer equipment and office equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	119,354	170,946
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 152,217	$ 142,032

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Depreciation	$ 105,841	$ 67,856	$ 38,258

Notes Payable - Additional Info

Notes Payable - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2010
Debt Instrument [Line Items]
Note payable		$ 1,000,000
Promissory note [Member] | Pfizer Inc. [Member]
Debt Instrument [Line Items]
Note payable			$ 1,000,000
Debt instrument, interest rate	7.00%
Debt instrument, maturity date	Jul. 29, 2020

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended			12 Months Ended
	Apr. 30, 2015	Aug. 31, 2014	Jul. 31, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, value of shares issued under sales agreement				$ 2,612	$ 1,984
Net proceeds from the issuance of common stock	$ 21,400,000			$ 13,521,913	$ 22,305,226
Warrants exercisable, outstanding				149,704	149,704
Total remaining options available for future grant				600,191	593,531
Weighted-average fair value of options granted				$ 1.38	$ 4.31	$ 6.77
Total intrinsic value of stock options exercised				$ 100,000	$ 100,000	$ 500,000
Intrinsic value of options outstanding				5,300,000
Intrinsic value of options vested or expected to vest				4,500,000
Intrinsic value of options exercisable				$ 2,100,000
Common stock, shares issued				26,118,722	19,877,857
Accounts payable and accrued expenses				$ 5,311,093	$ 2,545,894
Stock-based compensation				3,353,456	$ 3,315,943	$ 2,330,660
Unrecognized compensation expense				$ 4,400,000
Weighted-average vesting term				1 year 9 months 18 days
2006 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance to employees, nonemployee directors and consultants				1,030,303
2013 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance to employees, nonemployee directors and consultants				1,000,000
Stock option plans, maximum term of plan				10 years
Stock option plans, remaining vesting period				3 years
Percentage of outstanding shares of common stock				5.00%
Total remaining options available for future grant				600,191
2013 Plan [Member] | Tranche right [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option plans, percentage of options vested			25.00%
2013 Warrants [Member] | Convertible promissory notes [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrant expiration date				May 30, 2018
2013 Warrants [Member] | Series B Preferred Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrant exercisable to purchase shares							1,124,026
2013 Warrants [Member] | Series B Preferred Stock [Member] | Convertible promissory notes [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of warrant per share							$ 0.90
Lender Warrants [Member] | Series B convertible preferred stock [Member] | Term Loan One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of warrant per share							$ 0.90
Warrant issued							111,112
Warrant expiration date				Jul. 3, 2023
Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued under sales agreement				6,155,721	4,174,805
Common Stock [Member] | 2013 Warrants [Member] | Convertible promissory notes [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of warrant per share			$ 7.43
Common Stock [Member] | Lender Warrants [Member] | Convertible promissory notes [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of warrant per share			$ 7.43
Warrants exercisable, outstanding			13,468
Follow on Offering [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued under sales agreement	4,025,000
Initial public offering of common stock, price per share	$ 5.75
Post IPO [Member] | Common Stock [Member] | 2013 Warrants [Member] | Convertible promissory notes [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants exercisable, outstanding			136,236
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Lower fair market value of purchase price share			85.00%
Common stock, shares issued				26,876	17,914	0
Accounts payable and accrued expenses				$ 4,521	$ 15,789	$ 13,167
Maximum [Member] | Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employee stock purchase plan, employees contribution			20.00%
Sales Agreement with MLV & Co LLC [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued under sales agreement				6,155,721	149,805
Net proceeds from the issuance of common stock				$ 13,500,000	$ 600,000
Sales Agreement with MLV & Co LLC [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, value of shares issued under sales agreement		$ 50,000,000
Percentage of commission of gross sales price per share		3.00%
Sales Agreement with MLV & Co LLC [Member] | Weighted Average [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, price per share				$ 2.26	$ 6.05

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Beginning balance	2,464,849	1,859,034	790,590
Number of Options, Granted	1,132,500	822,250	1,212,000
Number of Options, Exercised	(60,807)	(21,029)	(81,056)
Number of Options, Cancelled	(142,729)	(195,406)	(62,500)
Number of Options, Ending balance	3,393,813	2,464,849	1,859,034
Number of Options, Vested or expected to vest	3,139,848
Number of Options, Exercisable	1,781,525
Weighted-Average Exercise Price, Beginning balance	$ 6.54	$ 6.84	$ 4.01
Weighted-Average Exercise Price, Granted	1.96	6.03	8.41
Weighted-Average Exercise Price, Exercised	0.92	1.04	1.10
Weighted-Average Exercise Price, Cancelled	6.65	7.79	9.09
Weighted-Average Exercise Price, Ending balance	5.10	$ 6.54	$ 6.84
Weighted-Average Exercise Price, Vested	5.36
Weighted-Average Exercise Price, Vested, Exercisable	$ 6.03
Weighted-Average Remaining Contractual Term Outstanding	7 years 7 months 24 days
Weighted-Average Remaining Contractual Term Vested or expected to vest	7 years 6 months 29 days
Weighted-Average Remaining Contractual Term Exercisable	6 years 9 months 11 days

Stockholders' Equity - Summar39

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Warrants to purchase common stock	149,704	149,704
Common stock options issued and outstanding	3,393,813	2,464,849
Common stock authorized for future option grants	600,191	593,531
Common stock authorized for the ESPP	555,210	432,086
Total	4,698,918	3,640,170

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Cumulative change in ownership percentage	50.00%
Period for cumulative change in ownership percentage	3 years
Research credit carryforwards expiration year	2,026
Deferred tax asset, change in valuation allowance amount	$ 10.2	$ 10.3	$ 8.9
Minimum percentage of likelihood for uncertain tax position to be recognized	50.00%
Recognized interest or penalties on income tax	$ 0	$ 0	$ 0
Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	107.6
Research credit carryforwards	$ 5
Operating loss carryforwards expiration year	2,025
California [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 2.8
Operating loss carryforwards expiration year	2,016
Net operating loss carryforwards expiration, second year	2,017
Net operating loss carryforwards expiration, end year	2,028
State [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 80.7
Research credit carryforwards	$ 1.6
Operating loss carryforwards expiration year	2,015
Scenario Forecast [Member] | California [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards				$ 4.2

Income Taxes - Components of Co

Income Taxes - Components of Company's Deferred Tax Assets (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets
Net operating loss carryovers	$ 41,103,000	$ 33,007,000
Research and development tax credits	4,989,000	3,585,000
Intangibles	643,000	922,000
Stock options	2,071,000	1,614,000
Compensation	786,000	553,000
Other	486,000	212,000
Total gross deferred tax assets	50,078,000	39,893,000
Less valuation allowance	(50,078,000)	(39,893,000)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Statutory Tax Rates and Effective Tax Rates (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Statutory rate	34.00%	34.00%	34.00%
State tax, net of federal benefit	0.00%	5.83%	5.83%
Valuation allowance	(34.26%)	(42.48%)	(39.85%)
Other	0.26%	2.65%	0.02%
Effective tax rate	0.00%	0.00%	0.00%

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 981,380	$ 571,194	$ 457,106
Additions based on tax positions related to the current year	337,459	337,862	141,866
Additions for tax positions of prior years	0	72,324	0
Reductions for tax positions of prior years	0	0	(27,778)
Balance at end of year	$ 1,318,839	$ 981,380	$ 571,194

Collaboration and License Agr44

Collaboration and License Agreements - Additional Information (Detail) - Novartis [Member]	1 Months Ended
	Dec. 31, 2016USD ($)Deliverable
Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds to be received on exercise of option	$ 7,000,000
Maximum milestone payments to be received upon achievement of certain milestones	$ 650,000,000
Percentage of development costs	50.00%
Required prior written notice period for termination of collaboration agreement	180 days
Percentage of reduction in milestone and royalty payments	50.00%
Number of significant deliverables | Deliverable	2
Collaboration revenue recognized over the period from upfront payment received	$ 50,000,000
Collaboration revenue recognized over the period from option exercise fee	7,000,000
Collaboration Agreement [Member] | Upfront Payment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable payment received	50,000,000
Investment Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Debt instrument, maximum borrowing capacity	$ 15,000,000
Debt instrument, coupon rate	6.00%
Debt instrument, maturity date	Dec. 31, 2019
Debt instrument, conversion price percentage	120.00%
Number of days trailing average closing price of common stock immediately prior to the conversion date	20 days
Deferred revenue	$ 2,500,000
Investment Agreement [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of outstanding shares will receive upon debt instrument conversion	19.00%

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Postemployment Benefits [Abstract]
Defined contribution plan, Employees voluntary contributions, Amount	$ 171,517	$ 164,989	$ 130,769
Eligibility criteria for employees to participate in the plan	Employees are eligible to participate in the plan beginning on the first day of employment.

Commitments - Additional Inform

Commitments - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	May 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 31, 2010
Operating Leased Assets [Line Items]
Rent expense		$ 378,005	$ 339,053	$ 243,832
Amount payable upon the achievement of specified regulatory milestone					$ 18,000,000
Operating lease term July 2014 through December 2019 [Member]
Operating Leased Assets [Line Items]
Lease renewal term		5 years
Future minimum payments for noncancelable operating lease		$ 1,600,000
Operating lease term September 2015 through September 2020 [Member]
Operating Leased Assets [Line Items]
Percentage of base rent escalator	3.00%
Rent expense	$ 32,784
Lease agreement rent expense for future period	$ 39,268

Quarterly Financial Data - Summ

Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) - USD ($)	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 799,046																$ 799,046
Total operating expenses	9,976,735		$ 6,894,868		$ 6,484,622		$ 7,274,589		$ 6,039,966		$ 6,061,335		$ 6,064,479		$ 5,964,922		30,630,814	$ 24,130,702	$ 22,288,182
Total other (expense) income	54,187		27,958		13,477		2,705		(4,196)		(6,211)		7,225		(14,742)		98,327	(17,924)	(31,709)
Net loss	$ (9,123,502)		$ (6,866,910)		$ (6,471,145)		$ (7,271,884)		$ (6,044,162)		$ (6,067,546)		$ (6,057,254)		$ (5,979,664)		$ (29,733,441)	$ (24,148,626)	$ (22,319,891)
Net loss per share, basic and diluted	$ (0.35)	[1]	$ (0.31)	[1]	$ (0.30)	[1]	$ (0.35)	[1]	$ (0.30)	[1]	$ (0.31)	[1]	$ (0.31)	[1]	$ (0.38)	[1]	$ (1.31)	$ (1.30)	$ (1.44)
[1]	Net loss per share is computed independently for each quarter and the full year based upon respective shares outstanding; therefore, the sum of the quarterly net loss per share amounts may not equal the annual amounts reported.

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($)	Feb. 15, 2017	Jan. 24, 2017	Dec. 31, 2016
Promissory note [Member] | Pfizer Inc. [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate			7.00%
Debt instrument, maturity date			Jul. 29, 2020
Promissory note [Member] | Pfizer Inc. [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate		7.00%
Debt instrument, maturity date		Jul. 29, 2020
Prepayment of notes payable		$ 1,004,861
Convertible Promissory Note [Member] | Subsequent Event [Member] | Novartis [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate	6.00%
Debt instrument, maturity date	Dec. 31, 2019
Promissory note, principal amount	$ 15,000,000
Promissory note conversion, description	Novartis may convert the Note into shares of the Company’s common stock upon a change of control of the Company or termination of the Collaboration Agreement entered into between the parties in its entirety. If converted, the principal and accrued interest under the Note will convert into the Company’s common stock at a conversion price equal to 120% of the 20-day trailing average closing price per share of the common stock immediately prior to the conversion date. Upon the occurrence of certain events of default, the Note requires the Company to repay the principal amount of the Note and any unpaid accrued interest.
Principal and accrued interest of note to be converted into common stock at conversion price, in percentage	120.00%
Trailing period for average closing price per share of common stock	20 days