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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	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	2016
Document Fiscal Period Focus	FY
Trading Symbol	CNAT
Entity Registrant Name	Conatus Pharmaceuticals Inc.
Entity Central Index Key	0001383701
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 - 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) - $ / 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 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' 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 - USD ($)	12 Months Ended
Statements of Cash Flows - USD ($)	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

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

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). This guidance requires that an entity recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. For public companies, ASU No. 2014-09 is effective for annual reporting periods beginning after December 15, 2017 and interim periods within that reporting period. Early adoption is permitted for annual reporting periods beginning after December 15, 2016. The Company has engaged outside advisors to assist with its determination of the accounting for the Collaboration Agreement with Novartis under ASU No. 2014-09. At this time, the Company is not able to estimate any impact.

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. This guidance requires management to perform interim and annual assessments on whether there are conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year of the date the financial statements are issued. If such conditions or events exist, certain disclosures are required. ASU No. 2014-15 is effective for the annual period ending after December 15, 2016, and for annual and interim periods thereafter. The Company adopted this guidance effective December 31, 2016, as required. The adoption of this guidance had no impact on the Company’s financial statements and related disclosures.

In November 2015, the FASB issued ASU No. 2015-17, Balance Sheet Classification of Deferred Taxes. This guidance requires companies to classify all deferred tax assets and liabilities as noncurrent on the balance sheet, instead of separating deferred taxes into current and noncurrent amounts. The guidance may be adopted on either a prospective or retrospective basis. For public companies, ASU No. 2015-17 is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. Early adoption is permitted. The Company early adopted this guidance effective December 31, 2016. Due to the valuation allowance on all of the Company’s deferred tax assets, the adoption of this guidance had no impact on the Company’s financial statements and related disclosures.

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This guidance requires organizations that lease assets with lease terms of more than 12 months to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. The ASU also requires disclosures to give financial statement users information on the amount, timing and uncertainty of cash flows arising from leases, including qualitative and quantitative information. For public companies, ASU No. 2016-02 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. The Company is currently evaluating the impact of the pending adoption of ASU No. 2016-02 on its financial statements and related disclosures.

In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718). This guidance changes the accounting for certain aspects of stock-based compensation, including income taxes, forfeitures, tax withholding and classification on the statement of cash flows. For public companies, ASU No. 2016-09 is effective for annual and interim periods beginning after December 15, 2016. The Company has evaluated the impact of the pending adoption of ASU No. 2016-09 on its financial statements and related disclosures and determined the effect to be immaterial.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This guidance replaces the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 requires that companies record expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities through an allowance for credit losses. This guidance limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and also requires the reversal of previously recognized credit losses when estimated credit losses decline. ASU No. 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is available for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The Company has evaluated the impact of the pending adoption of ASU No. 2016-13 on its financial statements and related disclosures and has determined the effect to be immaterial.

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. This guidance addresses the presentation and classification of certain cash flow items, including the classification of cash receipts and payments that have aspects of more than one class of cash flows, to reduce the existing diversity in practice. ASU 2016-15 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. Early adoption is permitted. The Company is currently evaluating the impact of the pending adoption of ASU No. 2016-15 on its financial statements and related disclosures.

Fair Value Measurements

12 Months Ended

Dec. 31, 2016

Fair Value Disclosures [Abstract]

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.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Marketable Securities

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

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

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Stockholders' Equity

12 Months Ended

Dec. 31, 2016

Equity [Abstract]

Stockholders' Equity

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

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

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.

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⁾	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.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Use of Estimates

Concentrations of Credit Risk

Cash and Cash Equivalents

Marketable Securities

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

Long-Lived Assets

Revenue Recognition

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

Stock-Based Compensation

	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

Comprehensive Loss

Segment Reporting

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

Recent Accounting Pronouncements

- Definition

Disclosure of accounting policy for cash and cash equivalents, including the policy for determining which items are treated as cash equivalents. Other information that may be disclosed includes (1) the nature of any restrictions on the entity's use of its cash and cash equivalents, (2) whether the entity's cash and cash equivalents are insured or expose the entity to credit risk, (3) the classification of any negative balance accounts (overdrafts), and (4) the carrying basis of cash equivalents (for example, at cost) and whether the carrying amount of cash equivalents approximates fair value.

+ References + Details