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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 31, 2017
Document and Entity Information
Entity Registrant Name	CATABASIS PHARMACEUTICALS INC
Entity Central Index Key	0001454789
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		23,083,177
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 21,713	$ 23,596
Available-for-sale securities		14,931
Prepaid expenses and other current assets	1,099	1,001
Total current assets	22,812	39,528
Property and equipment, net	388	568
Restricted cash	113	113
Total assets	23,313	40,209
Current liabilities:
Accounts payable	1,202	1,405
Accrued expenses	2,740	3,677
Current portion of notes payable, net of discount	3,296	3,243
Other liability	321
Total current liabilities	7,559	8,325
Deferred rent, net of current portion	97	53
Notes payable, net of current portion and discount		2,479
Other liability		266
Total liabilities	7,656	11,123
Commitments (Note 7)
Stockholders' equity:
Preferred stock, $0.001 par value per share, 5,000,000 shares authorized and no shares issued and outstanding
Common stock, $0.001 par value per share, 150,000,000 shares authorized; 22,895,033 and 18,817,572 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively	23	19
Additional paid-in capital	181,571	173,141
Accumulated other comprehensive loss		(4)
Accumulated deficit	(165,937)	(144,070)
Total stockholders' equity	15,657	29,086
Total liabilities and stockholders' equity	$ 23,313	$ 40,209

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Condensed Consolidated Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, authorized	5,000,000	5,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized	150,000,000	150,000,000
Common stock, issued	22,895,033	18,817,572
Common stock, outstanding	22,895,033	18,817,572

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Consolidated Statements of Operations
Revenues	$ 250		$ 250
Operating expenses:
Research and development	4,776	$ 5,936	14,693	$ 19,190
General and administrative	2,426	2,347	7,189	7,695
Total operating expenses	7,202	8,283	21,882	26,885
Loss from operations	(6,952)	(8,283)	(21,632)	(26,885)
Other (expense) income:
Interest expense	(105)	(199)	(381)	(662)
Interest and investment income	45	50	128	183
Other (expense) income, net	(5)	13	18	82
Total other expense, net	(65)	(136)	(235)	(397)
Net loss	$ (7,017)	$ (8,419)	$ (21,867)	$ (27,282)
Net loss per share - basic and diluted (in dollars per share)	$ (0.31)	$ (0.54)	$ (1.03)	$ (1.77)
Weighted-average common shares outstanding used in net loss per share - basic and diluted (in shares)	22,563,174	15,512,608	21,163,591	15,407,747

Condensed Consolidated Statements Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Consolidated Statements of Comprehensive Loss
Net loss	$ (7,017)	$ (8,419)	$ (21,867)	$ (27,282)
Other comprehensive (loss) income:
Unrealized (loss) gain on available-for-sale securities		(12)	4	(3)
Total other comprehensive (loss) income:		(12)	4	(3)
Comprehensive loss	$ (7,017)	$ (8,431)	$ (21,863)	$ (27,285)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net loss	$ (21,867)	$ (27,282)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	237	300
Stock-based compensation expense	1,501	1,575
Accretion of discount/premium on investment securities	26	107
Non-cash interest expense	128	218
Gain on sale of fixed assets	(30)	(49)
Changes in assets and liabilities:
Prepaid expenses and other current assets	(98)	(147)
Accounts payable	(203)	178
Accrued expenses	(903)	252
Deferred rent	10	(26)
Net cash used in operating activities	(21,199)	(24,874)
Investing activities
Purchases of available-for-sale securities		(41,497)
Sales and maturities of available-for-sale securities	14,910	20,584
Purchases of property and equipment	(57)	(436)
Sale of property and equipment	30	49
Net cash provided by (used in) investing activities	14,883	(21,300)
Financing activities
Proceeds from registered direct offering, net of issuance costs		10,730
Proceeds from at-the-market offering, net of issuance costs	6,910	1,483
Proceeds from exercise of common stock options and warrants	23	145
Payments on borrowing	(2,500)	(2,500)
Net cash provided by financing activities	4,433	9,858
Net decrease in cash and cash equivalents	(1,883)	(36,316)
Cash and cash equivalents, beginning of period	23,596	62,780
Cash and cash equivalents, end of period	21,713	26,464
Supplemental disclosure of cash flow information
Cash paid for interest	$ 269	661
Non-cash financing activities
At-the-market offering costs in accounts payable and accrued liabilities		157
Registered direct offering costs in accounts payable and accrued liabilities		$ 123

Organization and Operations	9 Months Ended
Organization and Operations	Sep. 30, 2017
Organization and Operations
Organization and Operations	1. Organization and Operations The Company Catabasis Pharmaceuticals, Inc. (the “Company”) is a clinical-stage biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutics based on the Company’s proprietary Safely Metabolized And Rationally Targeted, or SMART, linker drug discovery platform. The Company’s SMART LinkerSM technology platform enables the Company to engineer product candidates that can simultaneously modulate multiple targets in a disease. The Company’s proprietary product candidates impact pathways that are central to diseases where efficacy may be optimized by a multiple target approach. The Company’s primary focus is on treatments for rare diseases. The Company has applied its SMART Linker drug discovery platform to build an internal pipeline of product candidates for rare diseases and plans to pursue partnerships to develop additional product candidates. The Company was incorporated in the State of Delaware on June 26, 2008. Liquidity In August 2016, the Company entered into a sales agreement with Cowen and Company LLC, (“Cowen”), pursuant to which the Company may issue and sell shares of common stock for an aggregate maximum offering amount of $10.0 million under an at-the-market offering program (the “First ATM Program”). In March, 2017, the Company reduced the maximum amount of the offering under the First ATM Program to $8.8 million, which was fully utilized as of September 30, 2017. In October 2017, the Company entered into a second sales agreement with Cowen pursuant to which the Company may issue and sell shares of common stock for an aggregate maximum offering amount of $10.0 million under a second at-the-market offering program (the “Second ATM Program”). Cowen is not required to sell any specific amount, but acts as the Company’s sales agent using commercially reasonable efforts consistent with its normal trading and sales practices. Shares sold pursuant to the sales agreement have been sold pursuant to a shelf registration statement, which became effective on July 19, 2016. The Company pays Cowen 3% of the gross proceeds from any common stock sold through these sales agreements. During the nine months ended September 30, 2017, the Company sold an aggregate of 4,054,582 shares of common stock pursuant to the First ATM Program, at an average price of $1.77 per share, for gross proceeds of $7.2 million, resulting in net proceeds of $6.9 million after deducting sales commissions and offering expenses. As of September 30, 2017, the Company had an accumulated deficit of $165.9 million. The Company has been primarily involved with research and development activities and has incurred operating losses and negative cash flows from operations since its inception. The Company is subject to a number of risks including, but not limited to, the need to obtain adequate additional funding, including the resources necessary to fund a global Phase 3 trial of edasalonexent in DMD, which the Company plans to begin in the first half of 2018 with top-line results expected in 2020. The Company is currently exploring various avenues to secure capital to advance edasalonexent into Phase 3 trials, and our Phase 3 development activities will be dependent on securing adequate capital resources. The Company is also subject to a number of risks similar to other life science companies, including, but not limited to, successful discovery and development of its drug candidates, raising additional capital, development by its competitors of new technological innovations, protection of proprietary technology and regulatory approval and market acceptance of the Company’s products. The Company anticipates that it will continue to incur significant operating losses for the next several years as it continues to develop its product candidates. The Company adopted Accounting Standards Update (“ASU”) No. 2014-15, Presentation of Financial Statements—Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (“ASU 2014-15”) in connection with the issuance of its consolidated financial statements for the year ended December 31, 2016. As of September 30, 2017, the Company had available cash and cash equivalents of $21.7 million. The Company’s current operating plan provides for cash to fund operations through August 2018. Management expects to seek additional funds through equity or debt financings or through collaboration or licensing transactions. The Company may be unable to obtain equity or debt financings or enter into collaboration or licensing transactions and, if necessary, the Company will be required to implement cost reduction strategies, including ceasing or delaying development of the Company’s product candidates. These factors raise substantial doubt about the Company’s ability to continue as a going concern for a period of at least twelve months from the date of issuance of these consolidated financial statements. The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty. The Company will require substantial additional capital to fund operations. The Company has not generated any product revenues and has financed its operations primarily through public offerings and private placements of its equity securities. There can be no assurance that the Company will be able to obtain additional debt or equity financing or generate product revenue or revenues from collaborative partners, on terms acceptable to the Company, on a timely basis or at all. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2017

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying financial statements and the related disclosures are unaudited and have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”). Additionally, certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted from this report. Accordingly, these condensed financial statements should be read in conjunction with the financial statements as of and for the year ended December 31, 2016 and notes thereto, included in the Company’s annual report on Form 10-K filed with the Securities and Exchange Commission on March 16, 2017 (the “2016 Annual Report on Form 10-K”).

The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of the Company’s management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary to fairly present the Company’s financial position as of September 30, 2017, the results of its operations for the three and nine months ended September 30, 2017 and 2016 and its cash flows for the nine months ended September 30, 2017 and 2016. Such adjustments are of a normal and recurring nature. The results for the three and nine months ended September 30, 2017 are not necessarily indicative of the results for the year ending December 31, 2017, or for any future period.

The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, Catabasis Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of the Company’s condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ from such estimates.

The Company utilizes certain estimates to record expenses relating to research and development contracts. These contract estimates, which are primarily related to the length of service of each contract, are determined by the Company based on input from internal project management, as well as from third-party service providers.

Revenue Recognition

Effective January 1, 2017, the Company adopted Accounting Standards Codification (“ASC”), Revenue from Contracts with Customers, (“ASC 606”). This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under the agreement, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that it will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

Stock-Based Compensation

The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all share-based payments to employees, including grants of employee stock options, to be recognized in the statements of operations based on their grant date fair values. For stock options granted to employees and to members of the board of directors for their services on the board of directors, the Company estimates the grant date fair value of each option award using the Black-Scholes option-pricing model. The use of the Black-Scholes option-pricing model requires management to make assumptions with respect to the expected term of the option, the expected volatility of the Common Stock consistent with the expected life of the option, risk-free interest rates and expected dividend yields of the Common Stock.

For awards subject to service-based vesting conditions, the Company recognizes stock-based compensation expense equal to the grant date fair value of stock options on a straight-line basis over the requisite service period.

Share-based payments issued to non-employees are recorded at their fair values, and are periodically revalued as the equity instruments vest and are recognized as expense over the related service period in accordance with the provisions of ASC Topic 505, Equity. For equity instruments granted to non-employees, the Company recognizes stock-based compensation expense on a straight-line basis.

During the three and nine months ended September 30, 2017 and 2016, the Company recorded stock-based compensation expense for employee and non-employee stock options, which was allocated as follows in the condensed consolidated statements of operations (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development	$	198	$	182	$	595	$	533
General and administrative	317		328		906		1,042

Total	$	515	$	510	$	1,501	$	1,575

Net Loss Per Share

Basic net loss per share is calculated by dividing net loss by the weighted average shares outstanding during the period, without consideration for Common Stock equivalents. Diluted net loss per share is calculated by adjusting weighted average shares outstanding for the dilutive effect of Common Stock equivalents outstanding for the period, determined using the treasury-stock method. For purposes of the Company’s dilutive net loss per share calculation, stock options and warrants to purchase Common Stock were considered to be Common Stock equivalents but were excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive; therefore, basic and diluted net loss per share were the same for all periods presented.

The following Common Stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2016	2017	2016
Stock options	2,839,407	2,486,409	2,839,407	2,486,409
Common stock warrants	24,566	24,566	24,566	24,566

	2,863,973	2,510,975	2,863,973	2,510,975

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers, (“ASU 2014-09”). The standard replaces existing revenue recognition standards and significantly expand the disclosure requirements for revenue arrangements. The Company early adopted the standard on January 1, 2017 using the retrospective method. The adoption of the new standard did not have an effect on previously issued financial statements as the Company had not previously recognized revenue in its historical financial statements.

In February 2016, the FASB issued ASU 2016-02, Leases. This standard amends the existing guidance to require lessees to present most leases on their balance sheets but recognize corresponding expenses on their statements of operations. It is effective for annual reporting periods beginning after December 15, 2018, but early adoption is permitted. The Company is currently evaluating the impact that this standard will have on its consolidated financial statements.

In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting. This standard amends the existing guidance in an attempt to simplify several aspects of accounting for employee share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The Company adopted the standard on January 1, 2017. The amended guidance eliminates the requirement that excess tax benefits be realized as a reduction in current taxes payable before the associated tax benefit can be recognized in additional paid-in capital. This created approximately $0.2 million of deferred tax assets relating to federal and state net operating losses that were fully offset by a corresponding increase in the valuation allowance. As a result, there was no cumulative effect adjustment to accumulated deficit. The implementation of ASU 2016-09 does not have a material impact on stock-based compensation expense. As part of the adoption of ASU 2016-09, the Company elected to record forfeitures as they occur, which did not have a material impact on the consolidated financial statements upon adoption.

In May 2017, the FASB issued ASU 2017-09, Scope of Modification Accounting. This standard provides clarity on whether the change in existing terms and conditions of a share-based award require application of the guidance in ASC Topic 718, Compensation- Stock Compensation. It is effective for annual reporting periods beginning after December 15, 2017, but early adoption is permitted. The Company early adopted the standard in the period ending June 30, 2017. As of September 30, 2017, there was no material impact on the Company’s consolidated financial statements, and any future impact from adoption will be dependent on future transactions involving modifications of share-based awards.

Summary of Significant Accounting Policies

The Company’s significant accounting policies are described in Note 2, “Summary of Significant Accounting Policies,” in the 2016 Annual Report on Form 10-K, and there were no significant changes to such policies in the three and nine months ended September 30, 2017 that had a material impact on the Company’s results of operations or financial position.

Financial Instruments

9 Months Ended

Sep. 30, 2017

Financial Instruments

Financial Instruments

3. Financial Instruments

The tables below present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2017 and December 31, 2016 and indicate the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value. In general, fair values determined by Level 1 inputs utilize observable inputs such as quoted prices in active markets for identical assets or liabilities. Fair values determined by Level 2 inputs utilize data points that are either directly or indirectly observable, such as quoted prices, interest rates and yield curves. Fair values determined by Level 3 inputs utilize unobservable data points in which there is little or no market data, which require the Company to develop its own assumptions for the asset or liability. There were no transfers between fair value measurement levels during the three and nine months ended September 30, 2017 or 2016.

The Company’s investment portfolio includes fixed income securities that do not always trade on a daily basis. As a result, the pricing services used by the Company apply other available information as applicable through processes such as benchmark yields, benchmarking of like securities, sector groupings and matrix pricing to prepare valuations. In addition, model processes are used to assess interest rate impact and develop prepayment scenarios. These models take into consideration relevant credit information, perceived market movements, sector news and economic events. The inputs into these models may include benchmark yields, reported trades, broker-dealer quotes, issuer spreads and other relevant data. The Company validates the prices provided by its third party pricing services by obtaining market values from other pricing sources and analyzing pricing data in certain instances. The Company also invests in certain reverse repurchase agreements which are collateralized by deposits in the form of Government Securities and Obligations for an amount not less than 102% of their value. The Company does not record an asset or liability for the collateral as the Company is not permitted to sell or re-pledge the collateral. The collateral has at least the prevailing credit rating of US Government Treasuries and Agencies. The Company utilizes a third party custodian to manage the exchange of funds and ensure that collateral received is maintained at 102% of the value of the reverse repurchase agreements on a daily basis.

The Company determines the fair value of U.S. reverse repurchase agreements, corporate debt securities, and available-for-sale securities using Level 2 inputs. Below is a summary of assets measured at fair value on a recurring basis (in thousands):

	As of September 30, 2017
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total

Assets:
Cash and cash equivalents:
Money market funds	$	11,866	$	—	$	—	$	11,866
Corporate debt securities	—		2,655		—		2,655
U.S. reverse repurchase agreements	—		5,000		—		5,000

Total assets	$	11,866	$	7,655	$	—	$	19,521

	As of December 31, 2016
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total

Assets:
Cash and cash equivalents:
Money market funds	$	22,423	$	—	$	—	$	22,423
Available-for-sale securities:
Corporate debt securities	—		13,930		—		13,930
U.S. government-sponsored securities	—		1,001		—		1,001

Total assets	$	22,423	$	14,931	$	—	$	37,354

At September 30, 2017, the Company’s cash equivalents consisted of money market funds, U.S. reverse repurchase agreements, and corporate debt securities. At December 31, 2016, the Company’s cash equivalents consisted of money market funds. At September 30, 2017, and December 31, 2016, cash equivalents approximated their fair value due to their short-term nature.

At September 30, 2017 and December 31, 2016, the carrying value of the Company’s debt approximated fair value, which was determined using Level 3 inputs, including a quoted interest rate.

- 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

Available-for-Sale Securities

9 Months Ended

Sep. 30, 2017

Available-for-Sale Securities

Available-for-Sale Securities

4. Available-for-Sale Securities

As of September 30, 2017, the Company held no available-for-sale securities. The following table summarizes the available-for-sale securities held at December 31, 2016 (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
December 31, 2016
Corporate debt securities	$	13,934	$	—	$	(4	)	$	13,930
U.S. government-sponsored securities	1,001		—		—			1,001

Total	$	14,935	$	—	$	(4	)	$	14,931

The contractual maturities of all available-for-sale securities held at December 31, 2016 were one year or less. There were fifteen available-for-sale securities in an unrealized loss position at December 31, 2016, none of which had been in an unrealized loss position for more than 12 months. The aggregate fair value of these securities at December 31, 2016 was approximately $13.0 million. The Company reviews its investments for other-than-temporary impairment whenever the fair value of an investment is less than amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other-than-temporary, the Company considers whether it has the ability and intent to hold the investment until a market price recovery and considers whether evidence indicating the cost of the investment is recoverable outweighs evidence to the contrary. The Company did not hold any securities with other-than-temporary impairment at December 31, 2016.

Gross realized gains and losses on the sales of available-for-sale securities are included in other income, net. Unrealized holding gains or losses for the period that have been included in accumulated other comprehensive income, as well as gains and losses reclassified out of accumulated other comprehensive income into other income, net were not material to the Company’s condensed consolidated results of operations. The cost of securities sold or the amount reclassified out of the accumulated other comprehensive income into other income, net is based on the specific identification method for purposes of recording realized gains and losses. During the nine month period ended September 30, 2016 the Company received $7.8 million in proceeds from sales of available-for-sale securities, respectively. There were no proceeds from sales of available-for-sale securities in the three and nine month periods ended September 30, 2017 and the three month period ended September 30, 2016. All proceeds in the three and nine month periods ended September 30, 2017 were related to maturities of $14.9 million. The gains on proceeds from sales and maturities of available-for-sale securities were not material to the Company’s condensed consolidated results of operations during the three and nine month periods ending September 30, 2017 and 2016.

- Definition

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

+ References + Details

Accrued Expenses

9 Months Ended

Sep. 30, 2017

Accrued Expenses

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following (in thousands):

	September 30,		December 31,
	2017		2016
Accrued compensation	$	1,280	$	1,252
Accrued contracted research costs	1,192		1,850
Accrued professional fees	201		215
Accrued other	67		360

Total	$	2,740	$	3,677

Notes Payable

9 Months Ended

Sep. 30, 2017

Notes Payable

Notes Payable

6. Notes Payable

On August 27, 2014, the Company entered into a credit facility with MidCap Financial Trust, Flexpoint MCLS SPV LLC and Square 1 Bank, which was subsequently amended in March and December 2015 (as amended, the “Credit Facility”). The Credit Facility provided for initial borrowings of $5.0 million under a term loan (“Term Loan A”) and additional borrowings of up to $20.0 million under other term loans, for a maximum of $25.0 million. On August 27, 2014, the Company received proceeds of $5.0 million from the issuance of promissory notes under Term Loan A. On March 31, 2015, the Company received proceeds of $5.0 million from the issuance of promissory notes under another term loan (“Term Loan B”). The remaining amounts available for borrowing under this arrangement expired unused as of July 31, 2015, leaving total borrowings under the Credit Facility at $10.0 million. All amounts outstanding under the Credit Facility are due on October 1, 2018 and are collateralized by substantially all of the Company’s personal property, other than its intellectual property.

Interest-only payments were due monthly on amounts outstanding under the Credit Facility until September 1, 2015 and, thereafter, interest and principal payments are due in 36 equal monthly installments from October 1, 2015 through September 1, 2018. Amounts due under the Credit Facility bear interest at an annual rate of 7.49%. In addition, a final payment equal to 3.48% of any amounts drawn under the Credit Facility is due upon the earlier of the maturity date, acceleration of the term loans or prepayment of all or part of the term loans. The final payment is being accrued as additional interest expense using the effective-interest method from the date of issuance through the maturity date, and is recorded within other current liabilities. In the event of prepayment, the Company is obligated to pay 1% to 3% of the amount of the outstanding principal depending upon the timing of the prepayment. The effective interest rate as of September 30, 2017 was 11.2%.

In conjunction with Term Loan A, the Company issued warrants (the “2014 Warrants”) to purchase 157,844 shares of series B convertible preferred stock. In conjunction with Term Loan B, the Company issued warrants (the “2015 Warrants”) to purchase an additional 157,844 shares of series B convertible preferred stock. Upon the closing of the Company’s initial public offering (the “IPO”) in June 2015, the warrants to purchase shares of convertible preferred stock to the lenders were automatically converted into warrants to purchase an aggregate of 24,566 shares of Common Stock at an exercise price of $12.2114 per share. The warrants were exercisable immediately and have seven-year lives. At issuance, the warrants were valued at $0.2 million using the Black-Scholes option-pricing model. They were recorded as debt discounts of $0.2 million and are being accreted as interest expense using the effective-interest method over the remaining term of the loans.

There are no financial covenants associated with the Credit Facility; however, there are negative covenants restricting the Company’s activities, including limitations on asset dispositions, mergers or acquisitions; encumbering or granting a security interest in its intellectual property; incurring indebtedness or liens; paying dividends; making certain investments; and entering into certain other business transactions.

Upon the occurrence and continuation of an event of default, the lenders have the right to exercise certain remedies against the Company and the collateral securing the loans under the Credit Facility, including cash. Events of default include, among other things, failure to pay amounts due under the Credit Facility, insolvency, the occurrence of a material adverse event, which includes a material adverse change in the business, operations or conditions (financial or otherwise) of the Company or a material impairment of the prospect of repayment of any portion of the obligations, the occurrence of any default under certain other indebtedness and a final judgment against the Company in an amount greater than $250,000. The occurrence of a material adverse event could result in acceleration of the payment of the debt. At September 30, 2017 and December 31, 2016, the Company concluded that the likelihood of the acceleration of the debt was remote, as a material adverse event had not occurred and was unlikely to occur and therefore the debt was classified in current and long-term liabilities based on scheduled principal payments. Following the occurrence and during the continuance of an event of default, borrowings under the Credit Facility shall bear interest at a rate per annum, which is five hundred basis points, or 5.00%, above the rate that is otherwise applicable.

The Company assessed all terms and features of the Credit Facility in order to identify any potential embedded features that would require bifurcation or any beneficial conversion features. As part of this analysis, the Company assessed the economic characteristics and risks of the Credit Facility, including put and call features. The Company determined that all features of the Credit Facility were clearly and closely associated with a debt host and did not require bifurcation as a derivative liability, or the fair value of the feature was immaterial to the Company’s financial statements. The Company reassesses the features on a quarterly basis to determine if they require separate accounting.

Future principal payments at September 30, 2017 are as follows (in thousands):

Year Ending December 31,	Amount
Remainder 2017	833
2018	2,500

Total	$	3,333
Less: discount for warrants and costs paid to lenders	(37		)
Less: current portion	(3,296		)

Note payable, net of current portion and discount	$	—

During the three months ended September 30, 2017 and 2016, the Company recognized $0.1 million and $0.2 million of interest expense related to the Credit Facility, respectively. During the nine months ended September 30, 2017 and 2016, the Company recognized $0.4 million and $0.7 million of interest expense related to the Credit Facility, respectively.

Commitments

9 Months Ended

Sep. 30, 2017

Commitments

Commitments

7. Commitments

In November 2010, the Company entered into a five-year, non-cancelable operating lease for office and laboratory space that provided for a five-year extension upon the completion of the lease term. In December 2011, the Company signed a lease amendment (the “2011 Lease Amendment”) that expanded the leased premises beginning in the second quarter of 2012. The 2011 Lease Amendment also extended the term of the existing lease through June 30, 2017. The 2011 Lease Amendment includes a free rent period for the expansion premises and escalating rent payments. In July 2015, the Company signed another lease amendment (the “2015 Lease Amendment”) that expanded the leased premises beginning in the third quarter of 2015. The 2015 Lease Amendment includes escalating rent payments and is effective through June 30, 2017. In November 2016, the Company signed a third lease amendment (the “2016 Lease Amendment”). The 2016 Lease Amendment includes escalating rent payments and is effective through June 30, 2018. In August 2017, the Company signed a fourth lease amendment (the “2017 Lease Amendment”). The 2017 Lease Amendment includes escalating rent payments and is effective through June 30, 2020. The Company is recognizing rent expense on a straight-line basis over the lease term.

Future minimum payments required under the non-cancelable operating lease as of September 30, 2017 are summarized as follows (in thousands):

Period Ending December 31,	Amount
Remainder 2017	$	340
2018	1,379
2019	1,421
2020	721

Total minimum lease payments	$	3,861

Rent expense for the three months ended September 30, 2017 and 2016 was $0.4 million and $0.2 million, respectively. Rent expense for the nine months ended September 30, 2017 and 2016 was $1.0 million and $0.7 million, respectively.

Revenue Recognition	9 Months Ended
Revenue Recognition	Sep. 30, 2017
Revenue Recognition
Revenue Recognition	8. Revenue Recognition In August 2017, the Company entered into an option agreement (“Option Agreement”) with an unaffiliated party (“Recipient”), which is within the scope of ASC 606. Under the terms of the Option Agreement, the Company agreed to provide compound materials for certain of its product candidates and the right for the Recipient to use the materials to perform research during the term of the Option Agreement. At any point during the term of the Option Agreement, the Recipient may choose to exercise an option to enter into a license agreement with the Company, and the terms of the license agreement will be negotiated upon the exercise of such option. The Option Agreement includes a non-refundable up-front payment of $250 thousand. The term of the Option Agreement commenced in August 2017 and will continue upon additional payments of $250 thousand made by the Recipient, at its option, at the beginning of each of the next two quarterly periods. The option period will expire no later than 270 calendar days from the effective date, and may be terminated by the Recipient upon 30 days written notice. The Company concluded that the Option Agreement does not have any options to acquire additional goods or services that contain a material right. The Company evaluated the promised goods and services and determined the performance obligation should be recognized upon a transfer of control when the performance obligation has been satisfied at a point in time. During the three and nine months ended September 30, 2017, the Company recognized $250 thousand in revenue related to the option agreement. There were no contract assets or liabilities at September 30, 2017.

Preferred Stock	9 Months Ended
Preferred Stock	Sep. 30, 2017
Preferred Stock
Preferred Stock	9. Preferred Stock As of September 30, 2017, the Company had 5,000,000 shares of preferred stock authorized for issuance, $0.001 par value per share, with none issued or outstanding. Preferred stock may be issued from time to time in one or more series, each series to have such terms as stated or expressed in the resolutions providing for the issue of such series adopted by the board of directors of the Company. Preferred stock which may be redeemed, purchased or acquired by the Company may be reissued except as otherwise provided by law.

Common Stock Reserved for Future Issuance

9 Months Ended

Sep. 30, 2017

Common Stock Reserved for Future Issuance

Common Stock Reserved for Future Issuance

10. Common Stock Reserved for Future Issuance

The Company has reserved for future issuance the following shares of Common Stock:

	As of September 30,
	2017	2016
Warrants for the purchase of Common Stock	24,566	24,566
Options to purchase Common Stock	3,669,791	3,118,255
Employee Stock Purchase Plan	523,659	335,484

Total	4,218,016	3,478,305

Stock Incentive Plans

9 Months Ended

Sep. 30, 2017

Stock Incentive Plans

Stock Incentive Plans

11. Stock Incentive Plans

Prior to the IPO, the Company granted awards to eligible participants under its 2008 Equity Incentive Plan (“2008 Plan”). In May 2015, the Company’s board of directors adopted and, in June 2015, the Company’s stockholders approved the 2015 Stock Incentive Plan (“2015 Plan”), which became effective immediately prior to the effectiveness of the IPO. Subsequent to the IPO, option grants are awarded to eligible participants only under the 2015 Plan.

The 2015 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2015 Plan. The maximum number of shares of Common Stock that may be delivered in satisfaction of awards under the 2015 Plan is 1,068,287 shares, plus (1) 25,942 shares that were available for grant under the 2008 Plan immediately prior to the closing of the IPO, (2) the number of shares of Common Stock subject to outstanding awards under the 2008 Plan upon closing of the IPO that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right and (3) an annual increase, to be added the first day of each fiscal year, beginning with the fiscal year ending December 31, 2016 and continuing until, and including, the fiscal year ending December 31, 2025, equal to the lowest of 1,297,334 shares of Common Stock, 4% of the number of shares of Common Stock outstanding on the first day of the fiscal year and an amount determined by the Company’s board of directors. The January 1, 2017 and 2016 increases to the 2015 Plan added 752,702 and 612,531 authorized shares, respectively.

As of September 30, 2017, the Company had reserved 839,873 shares of Common Stock under the 2008 Plan, of which none remained available for future issuance. As of September 30, 2017, the Company had reserved 2,829,918 shares of Common Stock under the 2015 Plan, of which 830,384 shares remained available for future issuance. Under the 2015 Plan, stock options may not be granted with exercise prices at less than fair value on the date of the grant.

Terms of stock option agreements, including vesting requirements, are determined by the Company’s board of directors, subject to the provisions of the applicable stock incentive plan. Options granted by the Company generally vest ratably over four years, with a one-year cliff, and options are exercisable from the date of grant for a period of ten years. For options granted through September 30, 2017, the exercise price or purchase price, as applicable, equaled the estimated fair value of the Common Stock as determined by the Company’s board of directors on the date of grant.

A summary of the Company’s stock option activity and related information for employees and nonemployees follows:

	Shares		Weighted- Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016	2,270,169		$	6.11	8.14	$	613
Granted	876,740		$	1.24
Exercised	(22,879	)	$	1.01
Cancelled or forfeited	(284,623	)	$	7.27

Outstanding at September 30, 2017	2,839,407		$	4.54	7.99	$	817

Vested and Exercisable at September 30, 2017	1,172,834		$	5.82	6.67	$	53

The total intrinsic value of options exercised for the three months ended September 30, 2016 was $30 thousand. There were no options exercised in the three months ended September 30, 2017. The total intrinsic value of options exercised for the nine months ended September 30, 2017 and 2016 was $41 thousand and $0.2 million, respectively. The total fair value of employee and non-employee options vested was $0.6 million and $0.8 million for the three months ended September 30, 2017 and 2016, respectively. The total fair value of employee and non-employee options vested for the nine months ended September 30, 2017 and 2016 was $1.8 million and $1.9 million, respectively. The weighted-average grant date fair value of options granted to employees and non-employees for the three months ended September 30, 2017 and 2016 was $0.86 and $2.84, respectively. The weighted-average grant date fair value of options granted to employees and non-employees for the nine months ended September 30, 2017 and 2016 was $0.85 and $2.88, respectively.

At September 30, 2017 the total unrecognized compensation expense related to unvested stock option awards was $3.7 million. The Company expects to recognize that cost over a weighted-average period of approximately 2.1 years.

Employee Stock Purchase Plan

In June 2015, the Company’s board of directors adopted and the Company’s stockholders approved the 2015 Employee Stock Purchase Plan (the “2015 ESPP”) which became effective upon closing of the IPO. The 2015 ESPP initially authorized the issuance of up to a total of 182,352 shares of Common Stock to participating eligible employees. The number of authorized shares increases each January 1, commencing on January 1, 2016 and ending on December 31, 2026, by an amount equal to the lesser of one percent of the Company’s outstanding shares as of the first day of the applicable year, 364,705 shares and any lower amount determined by the Company’s board of directors. The January 1, 2017 and 2016 increases to the 2015 ESPP added 188,175 and 153,132 authorized shares, respectively. As of September 30, 2017, there had been no shares issued under the 2015 ESPP.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2017
Subsequent Events
Subsequent Events	12. Subsequent Events The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence for certain estimates and to identify matters that require additional disclosure. Subsequent events have been evaluated as required. Except as set forth below, there were no material recognized subsequent events recorded in the condensed consolidated financial statements as of and for the three and nine months ended September 30, 2017. Sales Agreement Subsequent to September 30, 2017, the Company sold an aggregate of 425,374 shares of common stock pursuant to the Second ATM Program, at an average price of $2.13 per share, for net proceeds of $0.9 million after deducting sales commissions and offering expenses.

Summary of Significant Accounting Polices (Polices)

9 Months Ended

Sep. 30, 2017

Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

Use of Estimates

Revenue Recognition

Stock-Based Compensation

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development	$	198	$	182	$	595	$	533
General and administrative	317		328		906		1,042

Total	$	515	$	510	$	1,501	$	1,575

Net Loss Per Share

The following Common Stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2016	2017	2016
Stock options	2,839,407	2,486,409	2,839,407	2,486,409
Common stock warrants	24,566	24,566	24,566	24,566

	2,863,973	2,510,975	2,863,973	2,510,975

Recent Accounting Pronouncements

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2017

Summary of Significant Accounting Policies

Schedule of stock-based compensation expense

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development	$	198	$	182	$	595	$	533
General and administrative	317		328		906		1,042

Total	$	515	$	510	$	1,501	$	1,575

Schedule of anti-dilutive common stock equivalents excluded from calculation of diluted net loss per share

	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2016	2017	2016
Stock options	2,839,407	2,486,409	2,839,407	2,486,409
Common stock warrants	24,566	24,566	24,566	24,566

	2,863,973	2,510,975	2,863,973	2,510,975

Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2017

Financial Instruments

Summary of assets measured at fair value on a recurring basis

Below is a summary of assets measured at fair value on a recurring basis (in thousands):

	As of September 30, 2017
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total

Assets:
Cash and cash equivalents:
Money market funds	$	11,866	$	—	$	—	$	11,866
Corporate debt securities	—		2,655		—		2,655
U.S. reverse repurchase agreements	—		5,000		—		5,000

Total assets	$	11,866	$	7,655	$	—	$	19,521

	As of December 31, 2016
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total

Assets:
Cash and cash equivalents:
Money market funds	$	22,423	$	—	$	—	$	22,423
Available-for-sale securities:
Corporate debt securities	—		13,930		—		13,930
U.S. government-sponsored securities	—		1,001		—		1,001

Total assets	$	22,423	$	14,931	$	—	$	37,354

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Available-for-Sale Securities (Tables)

9 Months Ended

Sep. 30, 2017

Available-for-Sale Securities

Summary of available-for-sale securities

The following table summarizes the available-for-sale securities held at December 31, 2016 (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
December 31, 2016
Corporate debt securities	$	13,934	$	—	$	(4	)	$	13,930
U.S. government-sponsored securities	1,001		—		—			1,001

Total	$	14,935	$	—	$	(4	)	$	14,931

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2017

Accrued Expenses

Schedule of components of accrued expenses

Accrued expenses consisted of the following (in thousands):

	September 30,		December 31,
	2017		2016
Accrued compensation	$	1,280	$	1,252
Accrued contracted research costs	1,192		1,850
Accrued professional fees	201		215
Accrued other	67		360

Total	$	2,740	$	3,677

Notes Payable (Tables)

9 Months Ended

Sep. 30, 2017

Notes Payable

Schedule of future principal payments

Future principal payments at September 30, 2017 are as follows (in thousands):

Year Ending December 31,	Amount
Remainder 2017	833
2018	2,500

Total	$	3,333
Less: discount for warrants and costs paid to lenders	(37		)
Less: current portion	(3,296		)

Note payable, net of current portion and discount	$	—

Commitments (Tables)

9 Months Ended

Sep. 30, 2017

Commitments

Schedule of future minimum payments under non-cancellable operating lease

Future minimum payments required under the non-cancelable operating lease as of September 30, 2017 are summarized as follows (in thousands):

Period Ending December 31,	Amount
Remainder 2017	$	340
2018	1,379
2019	1,421
2020	721

Total minimum lease payments	$	3,861

Common Stock Reserved for Future Issuance (Tables)

9 Months Ended

Sep. 30, 2017

Common Stock Reserved for Future Issuance

Schedule of Common Stock reserved for future issuance

	As of September 30,
	2017	2016
Warrants for the purchase of Common Stock	24,566	24,566
Options to purchase Common Stock	3,669,791	3,118,255
Employee Stock Purchase Plan	523,659	335,484

Total	4,218,016	3,478,305

Stock Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2017

Stock Incentive Plans

Summary of the Company's stock option activity

	Shares		Weighted- Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016	2,270,169		$	6.11	8.14	$	613
Granted	876,740		$	1.24
Exercised	(22,879	)	$	1.01
Cancelled or forfeited	(284,623	)	$	7.27

Outstanding at September 30, 2017	2,839,407		$	4.54	7.99	$	817

Vested and Exercisable at September 30, 2017	1,172,834		$	5.82	6.67	$	53

Organization and Operations - Liquidity (Details) $ / shares in Units, $ in Thousands		1 Months Ended	9 Months Ended
	Oct. 01, 2017 USD ($) $ / shares shares	Aug. 31, 2016 USD ($)	Sep. 30, 2017 USD ($) $ / shares shares	Oct. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Common stock offering
Accumulated deficit			$ (165,937)			$ (144,070)
Cash and Cash Equivalents, at Carrying Value			$ 21,713			$ 23,596	$ 26,464	$ 62,780
Common Stock \| Cowen
Common stock offering
Percentage of commission payable to underwriter based on proceeds from common stock		0.03
Common Stock \| First ATM Program
Common stock offering
Number of shares issued \| shares			4,054,582
Share price (in dollars per share) \| $ / shares			$ 1.77
Additional common stock issued			$ 7,200
Net proceeds			$ 6,900
Common Stock \| First ATM Program \| Cowen
Common stock offering
Aggregate maximum offering amount		$ 10,000			$ 8,800
Common Stock \| Second ATM Program \| Subsequent Events \| Cowen
Common stock offering
Aggregate maximum offering amount				$ 10,000
Number of shares issued \| shares	425,374
Share price (in dollars per share) \| $ / shares	$ 2.13
Net proceeds	$ 900

Summary of Significant Accounting Policies - Share-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-Based Compensation
Stock-based compensation expense	$ 515	$ 510	$ 1,501	$ 1,575
Research and development
Stock-Based Compensation
Stock-based compensation expense	198	182	595	533
General and administrative
Stock-Based Compensation
Stock-based compensation expense	$ 317	$ 328	$ 906	$ 1,042

Summary of Significant Accounting Policies - Net Loss Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Antidilutive common stock equivalents excluded from computation of diluted net loss per share
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	2,863,973	2,510,975	2,863,973	2,510,975
Stock options
Antidilutive common stock equivalents excluded from computation of diluted net loss per share
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	2,839,407	2,486,409	2,839,407	2,486,409
Common stock warrants
Antidilutive common stock equivalents excluded from computation of diluted net loss per share
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	24,566	24,566	24,566	24,566

Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - Accounting Standards Update 2016-09 $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
New Accounting Pronouncements
Deferred tax assets related to federal and state net operating losses	$ 0.2
Increase in valuation allowance	$ 0.2

Financial Instruments (Details) - USD ($) $ in Thousands	9 Months Ended
Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Financial Instruments
Transfers between fair value measurement levels	$ 0		$ 0
Cash and cash equivalents:
Cash and cash equivalents	21,713	$ 23,596	$ 26,464	$ 62,780
Available-for-sale securities:
Available-for-sale securities	$ 0	14,931
Corporate debt securities
Available-for-sale securities:
Available-for-sale securities		13,930
U.S. government-sponsored securities
Available-for-sale securities:
Available-for-sale securities		1,001
Government Securities and Obligations \| Reverse Repurchase Agreement \| Minimum
Financial Instruments
Percentage of investment amount to collateralized deposits value	102.00%
Recurring
Assets:
Total financial assets	$ 19,521	37,354
Recurring \| Money market funds
Cash and cash equivalents:
Cash and cash equivalents	11,866	22,423
Recurring \| Corporate debt securities
Cash and cash equivalents:
Cash and cash equivalents	2,655
Available-for-sale securities:
Available-for-sale securities		13,930
Recurring \| U.S. reverse repurchase agreements
Cash and cash equivalents:
Cash and cash equivalents	5,000
Recurring \| U.S. government-sponsored securities
Available-for-sale securities:
Available-for-sale securities		1,001
Recurring \| Level 1
Assets:
Total financial assets	11,866	22,423
Recurring \| Level 1 \| Money market funds
Cash and cash equivalents:
Cash and cash equivalents	11,866	22,423
Recurring \| Level 2
Assets:
Total financial assets	7,655	14,931
Recurring \| Level 2 \| Corporate debt securities
Cash and cash equivalents:
Cash and cash equivalents	2,655
Available-for-sale securities:
Available-for-sale securities		13,930
Recurring \| Level 2 \| U.S. reverse repurchase agreements
Cash and cash equivalents:
Cash and cash equivalents	$ 5,000
Recurring \| Level 2 \| U.S. government-sponsored securities
Available-for-sale securities:
Available-for-sale securities		$ 1,001

Available-for-Sale Securities (Details) $ in Thousands	3 Months Ended		9 Months Ended
Available-for-Sale Securities (Details) $ in Thousands	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) item
Available-for-Sale Securities
Amortized Cost					$ 14,935
Gross Unrealized Losses					(4)
Fair Value	$ 0		$ 0		$ 14,931
Number of available-for-sale securities in an unrealized loss position \| item					15
Number of available-for-sale securities in an unrealized loss position more than 12 months \| item					0
Unrealized loss position, available-for-sale securities					$ 13,000
Proceeds from sales of available-for-sale securities	0	$ 0	0	$ 7,800
Proceeds from sales and maturities of available-for-sale securities	$ 14,900		$ 14,910	$ 20,584
Corporate debt securities
Available-for-Sale Securities
Amortized Cost					13,934
Gross Unrealized Losses					(4)
Fair Value					13,930
U.S. government-sponsored securities
Available-for-Sale Securities
Amortized Cost					1,001
Fair Value					$ 1,001

Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accrued Expenses
Accrued compensation	$ 1,280	$ 1,252
Accrued contracted research costs	1,192	1,850
Accrued professional fees	201	215
Accrued other	67	360
Total	$ 2,740	$ 3,677

Notes Payable - Lines of Credit and Debt Instruments (Details) - USD ($)			1 Months Ended	9 Months Ended
	Mar. 31, 2015	Aug. 27, 2014	Jun. 30, 2015	Sep. 30, 2017
Term Loan A
Line of Credit Facility
Maximum borrowing capacity		$ 5,000,000
Proceeds from issuance of promissory notes		5,000,000
Term Loan B
Line of Credit Facility
Proceeds from issuance of promissory notes	$ 5,000,000
Other Term Loan
Line of Credit Facility
Maximum borrowing capacity		20,000,000
Credit Facility
Line of Credit Facility
Initial borrowings				$ 10,000,000
Maximum borrowing capacity		$ 25,000,000
Number of monthly payments (in number of payments)				36
Interest rate (as a percent)				7.49%
Percentage of amount outstanding due as a payment (as a percent)				3.48%
Effective interest rate (as a percent)				11.20%
Debt Instruments
Financial covenants				0
Final judgment amount that would trigger lender rights for remedy				$ 250,000
Basis spread				5.00%
Interest rate increase in the event of a default (as a percent)				5.00%
Minimum \| Credit Facility
Line of Credit Facility
Percentage of amount outstanding due as a payment (as a percent)				1.00%
Maximum \| Credit Facility
Line of Credit Facility
Percentage of amount outstanding due as a payment (as a percent)				3.00%
Warrant Liability
Debt Instruments
Exercise period			7 years
2014 and 2015 Warrants
Debt Instruments
Value of warrants			$ 200,000
Debt discounts			$ 200,000
2014 Warrants \| Term Loan A
Debt Instruments
Number of shares after conversion of issued warrants (in shares)				157,844
2015 Warrants \| Term Loan B
Debt Instruments
Number of shares after conversion of issued warrants (in shares)				157,844
Common stock warrants \| Initial public offering
Debt Instruments
Number of shares after conversion of issued warrants (in shares)			24,566
Exercise price of warrants (in dollars per share)			$ 12.2114

Notes Payable - Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Future principal payments
Remainder 2017	$ 833		$ 833
2018	2,500		2,500
Total	3,333		3,333
Less: discount for warrants and costs paid to lenders	(37)		(37)
Less: current portion	(3,296)		(3,296)
Notes payable, net of current portion and discount					$ 2,479
Credit Facility
Future principal payments
Interest expense	$ 100	$ 200	$ 400	$ 700

Commitments (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
Commitments (Details) - USD ($) $ in Thousands	Nov. 30, 2010	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating leases
Initial term of the operating lease for office and laboratory space	5 years
Extension term upon the completion of the initial lease term	5 years
Rent expense		$ 400	$ 200	$ 1,000	$ 700
Future minimum payments required under the non-cancellable operating lease
Remainder 2017		340		340
2018		1,379		1,379
2019		1,421		1,421
2020		721		721
Total minimum lease payments		$ 3,861		$ 3,861

Revenue Recognition (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
Revenue Recognition (Details) - USD ($) $ in Thousands	Aug. 31, 2017	Sep. 30, 2017	Sep. 30, 2017
Revenue recognition
Revenue recognized related to a Option agreement		$ 250	$ 250
Option agreement
Revenue recognition
Revenue recognized related to a Option agreement		$ 250	$ 250
Quarterly payment	$ 250
Option agreement expiration period	270 days
Option agreement termination period	30 days

Preferred Stock (Details)	9 Months Ended
Preferred Stock (Details)	Sep. 30, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares
Preferred Stock
Preferred stock, authorized	5,000,000	5,000,000
Preferred stock, par value (in dollars per share) \| $ / shares	$ 0.001	$ 0.001
Preferred Stock, Shares Issued(in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Minimum number of series used to issue preferred stock	1

Common Stock Reserved for Future Issuance (Details) - shares	Sep. 30, 2017	Sep. 30, 2016
Stockholders' equity
Shares reserved for future issuance (in shares)	4,218,016	3,478,305
Common stock warrants
Stockholders' equity
Shares reserved for future issuance (in shares)	24,566	24,566
Stock options
Stockholders' equity
Shares reserved for future issuance (in shares)	3,669,791	3,118,255
Employee Stock Purchase Plan
Stockholders' equity
Shares reserved for future issuance (in shares)	523,659	335,484

Stock Incentive Plans - Plan Information and Valuation Assumptions (Details) - shares			9 Months Ended
	Jan. 01, 2017	Jan. 01, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-Based Compensation
Shares reserved for future issuance (in shares)			4,218,016	3,478,305
2015 Plan
Stock-Based Compensation
Shares available for grant (in shares)			1,068,287
Shares reserved for future issuance (in shares)			2,829,918
Shares available for future issuance (in shares)			830,384
2015 Plan \| Annual minimum increase
Stock-Based Compensation
Shares available for grant (in shares)			1,297,334
Percentage of outstanding Common Stock available for issuance (as a percent)			4.00%
Potential increase in shares available for issuance as determined by the Board of Directors (in shares)	752,702	612,531
2008 Plan
Stock-Based Compensation
Shares available for grant (in shares)			25,942
Shares reserved for future issuance (in shares)			839,873
Shares available for future issuance (in shares)			0
Stock options
Stock-Based Compensation
Vesting period			4 years
Cliff period for vesting			1 year
Exercisable period			10 years

Stock Incentive Plans - Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Stock options
Outstanding at beginning of year (in shares)			2,270,169
Granted (in shares)			876,740
Exercised (in shares)			(22,879)
Cancelled or forfeited (in shares)			(284,623)
Outstanding at end of year (in shares)	2,839,407		2,839,407		2,270,169
Vested and Exercisable to vest at end of year (in shares)	1,172,834		1,172,834
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)			$ 6.11
Granted (in dollars per share)			1.24
Exercised (in dollars per share)			1.01
Cancelled or forfeited (in dollars per share)			7.27
Outstanding at end of year (in dollars per share)	$ 4.54		4.54		$ 6.11
Vested and Exercisable at end of year (in dollars per share)	$ 5.82		$ 5.82
Weighted Average Remaining Contractual Term (years)
Outstanding at end of year			7 years 11 months 27 days		8 years 1 month 21 days
Vested and Exercisable at end of year			6 years 8 months 1 day
Aggregate Intrinsic Value
Outstanding at the beginning of the year			$ 613
Outstanding at the end of the year	$ 817		817		$ 613
Aggregate intrinsic value of options vested and exercisable	53		53
Stock options
Unrecognized stock-based compensation expense
Intrinsic value of options exercised	0	$ 30	41	$ 200
Fair value of options vested	$ 600	$ 800	$ 1,800	$ 1,900
Weighted average grant date fair value of options granted (in dollars per share)	$ 0.86	$ 2.84	$ 0.85	$ 2.88
Unrecognized compensation expense related to unvested stock option awards	$ 3,700		$ 3,700
Weighted-average amortization period over which cost is expected to be recognized			2 years 1 month 6 days

Stock Incentive Plans - Employee Stock Purchase Plan (Details) - Common Stock - Employee Stock Purchase Plan - shares			1 Months Ended	9 Months Ended
	Jan. 01, 2017	Jan. 01, 2016	Jun. 30, 2015	Sep. 30, 2017
Stock-Based Compensation
Shares available for grant (in shares)			182,352
Number of shares issued (in shares)				0
Annual minimum increase
Stock-Based Compensation
Percentage of outstanding Common Stock available for issuance (as a percent)			1.00%
Potential increase in shares available for issuance as determined by the Board of Directors (in shares)	188,175	153,132	364,705

Subsequent Events (Details) - Second ATM Program - Cowen - Common Stock - Subsequent Events $ / shares in Units, $ in Millions	Oct. 01, 2017 USD ($) $ / shares shares
Subsequent Events
Number of shares issued \| shares	425,374
Share price (in dollars per share) \| $ / shares	$ 2.13
Net proceeds \| $	$ 0.9