Agile Therapeutics (AGXRW) 10-K 12 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Mar. 09, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	AGILE THERAPEUTICS INC
Entity Central Index Key	1,261,249
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 108
Entity Common Stock, Shares Outstanding		34,248,268
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 35,952	$ 48,750
Prepaid expenses	762	2,768
Total current assets	36,714	51,518
Property and equipment, net	13,863	12,330
Other assets	18	18
Total assets	50,595	63,866
Current liabilities:
Accounts payable	2,784	2,050
Accrued expenses	852	3,644
Loan payable, current portion	10,607	5,104
Warrant liability	29	172
Total current liabilities	14,272	10,970
Loan payable, long-term		10,607
Total liabilities	14,272	21,577
Commitments and contingencies (Note 12)
Stockholders' equity:
Common stock, $.0001 par value, 150,000,000 shares authorized, 34,186,342 and 28,759,731 issued and outstanding at December 31, 2017 and 2016, respectively	3	3
Additional paid-in capital	258,092	235,754
Accumulated deficit	(221,772)	(193,468)
Total stockholders' equity	36,323	42,289
Total liabilities and stockholders' equity	$ 50,595	$ 63,866

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Balance Sheets
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, authorized (in shares)	150,000,000	150,000,000
Common stock, issued (in shares)	34,186,342	28,759,731
Common stock, outstanding (in shares)	34,186,342	28,759,731

Statements of Operations

Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ 14,428	$ 20,929	$ 25,622
General and administrative	12,383	8,792	7,467
Total operating expenses	26,811	29,721	33,089
Loss from operations	(26,811)	(29,721)	(33,089)
Other income (expense)
Interest income	282	117	5
Interest expense	(1,918)	(2,446)	(2,077)
Change in fair value of warrants	143	234	(110)
Loss on extinguishment of debt			(1,036)
Total other income (expense), net	(1,493)	(2,095)	(3,218)
Loss before benefit from income taxes	(28,304)	(31,816)	(36,307)
Benefit from income taxes		3,075	5,972
Net loss	$ (28,304)	$ (28,741)	$ (30,335)
Net loss per share (basic and diluted) (in dollars per share)	$ (0.91)	$ (1.02)	$ (1.38)
Weighted-average common shares (basic and diluted) (in shares)	30,940,831	28,273,331	22,017,229

Statements of Changes in Stockh

Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common StockPrivate Placement	Common StockSecondary Public Offering	Common Stock	Additional Paid-in CapitalPrivate Placement	Additional Paid-in CapitalSecondary Public Offering	Additional Paid-in Capital	Deficit Accumulated During the Development stage	Private Placement	Secondary Public Offering	Total
Balance at Dec. 31, 2014			$ 2			$ 170,396	$ (134,392)			$ 36,006
Balance (in shares) at Dec. 31, 2014			18,634,872
Increase (decrease) in stockholders' equity
Share-based compensation - stock expense						2,965				2,965
Issuance of common stock, net of expenses				$ 19,330				$ 19,330
Issuance of common stock, net of expenses (in shares)	3,418,804
Fair value of common stock warrants issued with debt financing						1,184				1,184
Issuance of common stock upon exercise of options						593				593
Issuance of common stock upon exercise of options (in shares)			261,936
Net loss							(30,335)			(30,335)
Balance at Dec. 31, 2015			$ 2			194,468	(164,727)			29,743
Balance (in shares) at Dec. 31, 2015			22,315,612
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						3,425				3,425
Vesting of RSUs (in shares)			16,666
Issuance of common stock, net of expenses		$ 1			$ 37,527				$ 37,528
Issuance of common stock, net of expenses (in shares)		6,338,583
Issuance of common stock upon exercise of options						334				334
Issuance of common stock upon exercise of options (in shares)			88,870
Net loss							(28,741)			(28,741)
Balance at Dec. 31, 2016			$ 3			235,754	(193,468)			42,289
Balance (in shares) at Dec. 31, 2016			28,759,731
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						3,651				3,651
Vesting of RSUs (in shares)			16,667
Issuance of common stock, net of expenses					$ 18,535				$ 18,535
Issuance of common stock, net of expenses (in shares)		5,333,334
Issuance of common stock upon exercise of options						152				152
Issuance of common stock upon exercise of options (in shares)			76,610
Net loss							(28,304)			(28,304)
Balance at Dec. 31, 2017			$ 3			$ 258,092	$ (221,772)			$ 36,323
Balance (in shares) at Dec. 31, 2017			34,186,342

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (28,304)	$ (28,741)	$ (30,335)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	23	19	18
Noncash stock based compensation	3,651	3,425	2,965
Loss on extinguishment of debt			1,036
Noncash interest	667	946	590
Change in fair value of warrants	(143)	(234)	110
Changes in operating assets and liabilities:
Prepaid expenses and other assets	2,006	922	(1,209)
Accounts payable and accrued expenses	(2,460)	362	1,347
Net cash used in operating activities	(24,560)	(23,301)	(25,478)
Cash flows from investing activities:
Acquisition of property and equipment	(1,313)	(31)	(290)
Net cash used in investing activities	(1,313)	(31)	(290)
Cash flows from financing activities:
Proceeds from issuance term loan			16,265
Repayment of term loan			(15,784)
Principal payments of long-term debt	(5,612)	(985)
Return of principal payments of long-term debt		985
Proceeds from issuance of common stock, in public offering, net of offering costs	18,535	37,528
Proceeds from issuance of common stock, in private placement, net of offering costs			19,330
Cash paid for debt financing costs		(175)	(423)
Proceeds from exercise of stock options	152	334	593
Net cash provided by financing activities	13,075	37,687	19,981
Net (decrease) increase in cash and cash equivalents	(12,798)	14,355	(5,787)
Cash and cash equivalents, beginning of year	48,750	34,395	40,182
Cash and cash equivalents, end of year	35,952	48,750	34,395
Supplemental cash flow information
Interest paid during the year	1,295	$ 1,500	1,474
Non-cash transactions
Fair value of common stock warrants issued			$ 1,184
Property and equipment purchases included in accounts payable	$ 242

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2017
Organization and Description of Business
Organization and Description of Business	1. Organization and Description of Business Nature of Operations Agile Therapeutics, Inc. ("Agile" or the "Company") was incorporated in Delaware on December 22, 1997. Agile is a forward-thinking women's healthcare company dedicated to fulfilling the unmet health needs of today's women. The Company's activities since inception have consisted principally of raising capital and performing research and development. The Company is headquartered in Princeton, New Jersey. The Company's lead product candidate, Twirla®, also known as AG200-15, is a once-weekly prescription contraceptive patch that is at the end of Phase 3 clinical development. Substantially all of the Company's resources are currently dedicated to developing and seeking regulatory approval for Twirla. The Company has not generated product revenue to date and is subject to a number of risks similar to those of other early stage companies, including dependence on key individuals, the difficulties inherent in the development of commercially usable products, the potential need to obtain additional capital necessary to fund the development of its products, and competition from larger companies. The Company has incurred losses each year since inception. As of December 31, 2017, the Company had an accumulated deficit of approximately $221.8 million. The Company has financed its operations to date primarily through the issuance and sale of its common stock in both public and private offerings (see Note 8), private placements of its convertible preferred stock, venture loans, and non-dilutive grant funding. The Company expects to continue to incur net losses into the foreseeable future. Going Concern On December 21, 2017, the Company received a complete response letter (the "2017 CRL") from the FDA citing deficiencies related to the manufacturing process for Twirla, and raising questions on the in vivo adhesion properties of Twirla and their potential relationship to the Company's phase 3 clinical trial results. The Company's ability to commercialize Twirla, and the timing of Twirla commercialization, is dependent on FDA's review of the Company's response to the 2017 CRL and its NDA for Twirla, and other items such as timely and successful completion of the validation of equipment for commercial manufacturing, ultimate FDA approval, and additional capital. In January 2018, following the Company's receipt of the 2017 CRL, the Company significantly scaled back its preparations for commercialization of Twirla, including commercial pre-launch and manufacturing validation activities, pending its ability to address the 2017 CRL and receive approval of Twirla. The Company's current business plan assumes resubmission of its NDA for Twirla in the second quarter of 2018, a six-month FDA review of its NDA resubmission, and resumption of both pre-launch commercial activities and pre-validation and validation of the Company's manufacturing process after Twirla approval, if the FDA approves Twirla. The Company will require additional capital to fund operating needs beyond 2018, including among other items, the resumption and completion of our commercialization plan for Twirla, which primarily includes the validation of our commercial manufacturing process and the commercial launch of Twirla, if approved, and advancing the development of its other potential product candidates. The Company cannot assure you that the FDA will approve Twirla, that the FDA's timeline for review will be within six months, or that the Company along with Corium, its third-party manufacturer, will be able to complete validation of the Company's commercial manufacturing successfully and in a timely manner. The Company's ability to continue operations after December 31, 2018 will depend on its ability to obtain additional funding, as to which no assurances can be given. There can be no assurance that any financing by the Company can be realized by the Company, or if realized, what the terms of any such financing may be, or that any amount that the Company is able to raise will be adequate. Based upon the foregoing, there is substantial doubt about the Company's ability to continue as a going concern. As of December 31, 2017, the Company had cash and cash equivalents of $35.9 million. The Company continues to analyze various alternatives, including strategic and refinancing alternatives, asset sales and mergers and acquisitions. The Company's future success depends on its ability to raise capital and/or implement the various strategic alternatives discussed above. The Company cannot be certain that these initiatives or raising additional capital, whether through selling additional debt or equity securities or obtaining a line of credit or other loan, will be available to it or, if available, will be on terms acceptable to the Company. If the Company issues additional securities to raise funds, these securities may have rights, preferences, or privileges senior to those of its common stock, and the Company's current shareholders may experience dilution. If the Company is unable to obtain funds when needed or on acceptable terms, the Company may be required to curtail its current development programs, cut operating costs, forego future development and other opportunities and may need to seek bankruptcy protection. The audited financial statements as of December 31, 2017 have been prepared under the assumption that the Company will continue as a going concern for the next 12 months. The Company's ability to continue as a going concern is dependent upon its uncertain ability to obtain additional equity and/or debt financing and reduce expenditures. The accompanying financial statements as of December 31, 2017 do not include any adjustments that might result from the outcome of this uncertainty.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Polices Basis of Presentation The accompanying financial statements have been prepared in accordance with United States generally accepted accounting principles ("U.S. GAAP") and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented. Certain prior period amounts have been reclassified to conform to the current period presentation. Use of Estimates The preparation of the Company's financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company bases its estimates and judgments on historical experience and various other assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company's balance sheets and the amounts of expenses reported for each of the periods presented are affected by estimates and assumptions, which are used for, but not limited to, the accounting for common stock warrants, stock-based compensation, income taxes, and accounting for research and development costs. Actual results could differ from those estimates. Risks and Uncertainties Product candidates developed by the Company typically will require approval from the FDA prior to commercial sales. There can be no assurance that the Company's product candidates will receive the required approval. If the Company was denied approval or such approval was delayed, or is unable to obtain the necessary financing to complete development and approval, there will be a material adverse impact on the Company's financial condition and results of operations. Cash and Cash Equivalents The Company considers all highly-liquid investments with an original maturity of three months or less when purchased to be cash equivalents. All cash and cash equivalents are held in United States financial institutions. Cash and cash equivalents include money market funds that invest primarily in commercial paper and U.S. government and U.S. government agency obligations. The Company maintains balances with financial institutions in excess of the Federal Deposit Insurance Corporation limit. Fair Value of Financial Instruments In accordance with Accounting Standards Codification ("ASC") 825, Financial Instruments , disclosures of fair value information about financial instruments are required, whether or not recognized in the balance sheet, for which it is practicable to estimate that value. Cash and cash equivalents are carried at fair value (see Note 3). Financial instruments, including accounts payable and accrued liabilities, are carried at cost, which approximates fair value given their short-term nature. Property and Equipment Property and equipment, consisting of manufacturing, office and computer equipment, is stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line, method over the estimated useful lives of the assets. Expenditures incurred after the fixed assets have been put into operation, such as repairs and maintenance, are charged to earnings in the period in which costs are incurred. Improvements and additions are capitalized in accordance with Company policy. Long-Lived Assets In accordance with ASC 360, Property, Plant and Equipment , the Company's policy is to review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Management does not believe that there has been any impairment of the carrying value of any long-lived assets as of December 31, 2017. Research and Development Expense Research and development costs are expensed as incurred. Research and development expense consists primarily of costs related to personnel, including salaries and other personnel-related expenses, expenses related to manufacturing, clinical trial expenses, consulting fees and support services used in drug development. All research and development costs are charged to operations as incurred in accordance with ASC 730, Research and Development . In certain circumstances, the Company is required to make advance payments to vendors for goods or services that will be received in the future for use in research and development activities. In such circumstances, the advance payments are deferred and are expensed when the activity has been performed or when the goods have been received. Deferred Financing Costs Costs directly attributable to the Company's term loan (see Note 7) are deferred and reported as a reduction of the related term loan. These costs represent legal fees and other costs related to the term loan and are being amortized over the term of the loan. Amortization of deferred financing costs charged to interest expense was approximately $239, $256 and $211 for the years ended December 31, 2017, 2016 and 2015, respectively. Concentrations of Credit Risk Financial instruments which potentially subject the Company to credit risk consist principally of cash and cash equivalents. All cash and cash equivalents are held in business checking and money market accounts in United States financial institutions the balances of which exceed federally insured limits. The Company has not recognized any losses from credit risks on such accounts. The Company believes it is not exposed to significant credit risks on cash and cash equivalents. The Company has no financial instruments with off-balance sheet risk of accounting loss. Warrants The Company accounts for its warrants to purchase redeemable convertible stock in accordance with ASC 480, Distinguishing Liabilities from Equity . ASC 480 requires that a financial instrument, other than outstanding share, that, at inception, is indexed to an obligation to repurchase the issuer's equity shares, regardless of the timing or the probability of the redemption feature, and may require the issuer to settle the obligation by transferring assets be classified as a liability. The Company measures the fair value of its warrant liability using the Black-Scholes option pricing model with changes in fair value recognized as increases or reductions to other income (expense) in the statement of operations. In connection with the completion of the Company's initial public offering in May 2014, the warrants to purchase shares of Series A-1 and Series A-2 preferred stock expired unexercised and the warrants to purchase shares of Series C preferred stock automatically converted into warrants to purchase shares of common stock. Warrants with non-standard anti-dilution provisions (referred to as down round protection) are classified as liabilities and re-measured each reporting period. As of December 31, 2017, there were outstanding 62,505 warrants to purchase common stock at $6.00 per share. These warrants expire on December 14, 2019. The warrants issued in connection with the Company's debt financing completed in February 2015 (see Note 7) are classified as a component of stockholders' equity. The value of such warrants was determined using the Black-Scholes option-pricing model. As of December 31, 2017, there were outstanding 180,274 warrants to purchase common stock at $5.89 per share related to this debt financing. These warrants expire on February 24, 2020. Income Taxes The Company accounts for deferred taxes using the asset and liability method as specified by ASC 740, Income Taxes . Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and the tax basis of assets and liabilities, operating losses and tax credit carryforwards. Deferred income taxes are measured using the enacted tax rates and laws that are anticipated to be in effect when the differences are expected to reverse. The measurement of deferred income tax assets is reduced, if necessary, by a valuation allowance for any tax benefits which are not expected to be realized. The effect on deferred income tax assets and liabilities of a change in tax rates is recognized in the period that such tax rate changes are enacted. The Company has adopted the authoritative guidance on accounting for and disclosure of uncertainty in tax positions which prescribes a comprehensive model for the financial statement recognition, measurement, presentation and disclosure of uncertain tax positions taken or expected to be taken in income tax returns. The Company has no uncertain tax positions as of December 31, 2017 that qualifies for either recognition or disclosure in the financial statements under this guidance. Stock-Based Compensation The Company accounts for stock-based compensation in accordance with ASC 718, Compensation—Stock Compensation . The Company grants stock options for a fixed number of shares to employees and non-employees with an exercise price equal to the fair value of the shares at grant date. Compensation cost is recognized for all share-based payments granted and is based on the grant-date fair value estimated using the weighted-average assumption of the Black-Scholes option pricing model based on key assumptions such as stock price, expected volatility and expected term. The Company elects to account for forfeitures when they occur. The equity instrument is not considered to be issued until the instrument vests. As a result, compensation cost is recognized over the requisite service period with an offsetting credit to additional paid-in capital. The Company also awards restricted stock units ("RSUs") to employees and its board of directors (the "Board"). RSUs are generally subject to forfeiture if employment terminates prior to the completion of the vesting restrictions. The Company expenses the cost of the RSUs, which is determined to be the fair market value of the shares of common stock underlying the RSUs at the date of grant, ratably over the period during which the vesting restrictions lapse. Cost associated with performance-based restricted stock units with a performance condition which affects the vesting is recognized only if the performance condition is probable of being satisfied. Awards for consultants are accounted for under ASC 505-50, Equity Based Payments to Non-Employees . Any compensation expense related to consultants is marked-to-market over the applicable vesting period as they vest. Prior to May 22, 2014, the Company utilized various methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation , to estimate the fair value of its stock. The methodologies included an option pricing method and a probability-weighted expected return methodology that determined an estimated value under an initial public offering ("IPO") scenario and a sale scenario based upon an assessment of the probability of occurrence of each scenario. Each valuation methodology includes estimates and assumptions that require the Company's judgment. These estimates include assumptions regarding future performance, including the successful completion of clinical trials and the time to completing an IPO or sale of the Company. As with any valuation, significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating and reporting segment, which is the business of developing its transdermal patch for use in contraception. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding plus the effect of dilutive potential common shares outstanding during the period determined using the treasury-stock and if-converted methods. For purposes of diluted net loss per share calculation, common stock warrants, unvested RSUs and stock options are considered to be potentially dilutive securities but are excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive and therefore, basic and diluted net loss per share were the same for all periods presented. The following table sets forth the outstanding potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because to do so would be anti-dilutive (in common equivalent shares): Year Ended December 31, 2017 2016 2015 Common stock warrants Unvested restricted stock units — Common stock options ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board ("FASB") or other standard setting bodies that the Company adopts as of the specified effective date. Unless otherwise discussed below, the Company does not believe that the adoption of recently issued standards have or may have a material impact on our consolidated financial statements or disclosures. In May 2014, as part of its ongoing efforts to assist in the convergence of U.S. GAAP and International Financial Reporting Standards, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which is a new standard related to revenue recognition. Under the new standard, recognition of revenue occurs when a customer obtains control of promised services or goods in an amount that reflects the consideration to which the entity expects to receive in exchange for those goods or services. In addition, the standard requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from customer contracts. The standard must be adopted using either a full retrospective approach for all periods presented in the period of adoption or a modified retrospective approach. In July 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers—Deferral of the Effective Date , which defers the implementation of this new standard to be effective for fiscal years beginning after December 15, 2017. Early adoption is permitted effective January 1, 2017. In March 2016, the FASB issued ASU 2016-08, Principal versus Agent Considerations , which clarifies the implementation guidance on principal versus agent considerations in the new revenue recognition standard pursuant to ASU 2014-09. In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing , and in May 2016, the FASB issued ASU 2016-12, Narrow-Scope Improvements and Practical Expedients , which amend certain aspects of the new revenue recognition standard pursuant to ASU 2014-09. In December 2016, the FASB issued ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers to clarify the codification or to correct unintended application of guidance. In September and November 2017, the FASB issued ASU 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842) and ASU 2017-14, Income Statement—Reporting Comprehensive Income (Topic 220), Revenue Recognition (Topic 605), and Revenue from Contracts with Customers (Topic 606) which amends certain aspects of the new revenue recognition standard. As the Company has not recognized any revenue to date, the adoption did not have any impact on the Company's financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases . The new standard establishes a right-of-use ("ROU") model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the statement of operations. The new standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. A modified retrospective transition approach is required for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. In September 2017, the FASB issued ASU 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842) which amends certain aspects of the new lease standard. The Company is currently evaluating the impact of the pending adoption of the new standard on the Company's financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting to provide clarity and reduce both (1) diversity in practice and (2) cost and complexity when applying the guidance in Topic 718, Compensation—Stock Compensation , to change the terms or conditions of a share-based payment award. The amendments in this Update provide guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. This Update is the final version of Proposed ASU 2016-360 —Compensation—Stock Compensation (Topic 718)—Scope of Modification Accounting , which has been deleted. The amendments in this Update are effective for all entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted. This ASU is not expected to have a material impact on the Company's financial statements. In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part 1) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception." This ASU eliminates the requirement to consider "down round" features when determining whether certain equity-linked financial instruments or embedded features are indexed to an entity's own stock. ASU 2017-11 is effective for annual periods beginning after December 31, 2018. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of ASU 2017-11 on its financial statements. Management does not believe that any other recently issued, but not yet effective accounting pronouncements, if adopted, would have a material impact on the accompanying consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Measurements
Fair Value Measurements	3. Fair Value Measurements ASC 820, Fair Value Measurements and Disclosures , describes the fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. Assets and liabilities that are measured at fair value are reported using a three-level fair value hierarchy that prioritizes the inputs used to measure fair value. This hierarchy maximizes the use of observable inputs and minimizes the use of unobservable inputs. The three levels of inputs used to measure fair value are as follows: • Level 1—Quotes prices in active markets for identical assets and liabilities. The Company's Level 1 assets and liabilities consist of cash and cash equivalents. • Level 2—Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted market prices for similar assets or liabilities in active markets or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets and liabilities. The Company has no Level 2 assets or liabilities. • Level 3—Unobservable inputs that are supported by little or no market data and which require internal development of assumptions about how market participant price the fair value of the assets or liabilities. The Company's Level 3 liabilities consist of the warrant liability. The Company is required to mark the value of its warrant liability to market and recognize the change in valuation in its statements of operations each reporting period. The following tables set forth the Company's financial instruments measured at fair value by level within the fair value hierarchy as of December 31, 2017 and 2016: Level 1 Level 2 Level 3 2017 Assets: Cash equivalents $ $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total assets at fair value $ $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities: Common stock warrants $ — $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total liabilities at fair value $ — $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Level 1 Level 2 Level 3 2016 Assets: Cash equivalents $ $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total assets at fair value $ $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities: Common stock warrants $ — $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total liabilities at fair value $ — $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The significant assumptions used in preparing the option pricing model for valuing the Company's warrants as of December 31, 2017 include (i) volatility (70.0%), (ii) risk free interest rate of 1.89% (estimated using treasury bonds with a 2-year life), (iii) strike price ($6.00) for the common stock warrants, (iv) fair value of common stock ($2.69) and (v) expected life (2 years). The significant assumptions used in preparing the option pricing model for valuing the Company's warrants as of December 31, 2016 include (i) volatility (75.0%), (ii) risk free interest rate of 1.47% (estimated using treasury bonds with a 3-year life), (iii) strike price ($6.00) for the common stock warrants, (iv) fair value of common stock ($5.70) and (v) expected life (3 years). The following is a roll forward of the fair value of Level 3 warrants: Beginning balance at December 31, 2014 $ Change in fair value ​ ​ ​ ​ ​ Ending balance at December 31, 2015 Change in fair value ) ​ ​ ​ ​ ​ Ending balance at December 31, 2016 Change in fair value ) ​ ​ ​ ​ ​ Ending balance at December 31, 2017 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ There were no transfers between Level 1, 2 or 3 during 2017 or 2016. If the Company's estimates regarding the fair value of its warrants are inaccurate, a future adjustment to these estimated fair values may be required. Additionally, these estimated fair values could change significantly.

Prepaid Expenses

Prepaid Expenses	12 Months Ended
	Dec. 31, 2017
Prepaid Expenses
Prepaid Expenses	4. Prepaid Expenses Prepaid expenses consist of the following: December 31, 2017 2016 Prepaid clinical trial expense $ $ Prepaid insurance Other ​ ​ ​ ​ ​ ​ ​ ​ Total prepaid expenses $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property and Equipment
Property and Equipment	5. Property and Equipment Property and equipment, consisting of manufacturing, office and computer equipment, is stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line, method over the estimated useful lives of the assets. Property and equipment consist of the following: December 31, 2017 2016 Estimated Life Office equipment $ $ 3 - 10 years Computer equipment 3 years Manufacturing equipment 5 years ​ ​ ​ ​ ​ ​ ​ ​ ​ Less: accumulated depreciation ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ Property and equipment $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As December 31, 2017 and 2016, manufacturing equipment includes approximately $13.8 million and $12.4 million, respectively, of equipment which is in the process of being constructed and qualified and is not currently being depreciated.

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2017
Accrued Liabilities
Accrued Liabilities	6. Accrued Liabilities Accrued liabilities consist of the following: December 31, 2017 2016 Employee bonuses $ $ Accrued clinical trial costs — Accrued interest payable Accrued professional fees and other ​ ​ ​ ​ ​ ​ ​ ​ Total accrued liabilities $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Loan and Security Agreements

Loan and Security Agreements	12 Months Ended
	Dec. 31, 2017
Loan and Security Agreements
Loan and Security Agreements	7. Loan and Security Agreements Oxford Finance LLC In December 2012, the Company entered into a Loan and Security Agreement (the "Oxford Loan") with Oxford Finance LLC ("Oxford") pursuant to which the Company borrowed a total of $15.0 million from Oxford. The Oxford Loan accrued interest at a fixed annual rate equal to 9.20% (Three-month U.S. Libor rate of 0.47% plus 8.73%). Interest on the Oxford Loan was payable monthly and principal was due in 30 equal consecutive monthly installments beginning on February 1, 2015 and ending on July 1, 2017. In addition, the Company was required to make a final payment of $675 on the maturity date of the Oxford Loan (July 1, 2017). In connection with the Oxford Loan, the Company issued Oxford warrants to purchase 62,505 shares of common stock at $6.00 per share. These warrants expire on December 14, 2019. In February 2015, the Company terminated and repaid all amounts outstanding under the Oxford Loan and recorded a loss on the extinguishment of the Oxford Loan (see further discussion below). Hercules Capital, Inc. In February 2015, the Company entered into a loan and security agreement (the "Hercules Loan") with Hercules Capital, Inc. ("Hercules") for a term loan of up to $25.0 million. In August 2016, the Company entered into the First Amendment to Loan and Security Agreement (the "First Amendment") with Hercules which amends certain terms of the Hercules Loan. In May 2017, the Company entered into the Second Amendment to Loan and Security Agreement (the "Second Amendment") with Hercules which further amended certain terms of the Hercules Loan. A first tranche of $16.5 million was funded upon execution of the Hercules Loan, approximately $15.5 million of which was used to repay the Company's existing term loan with Oxford. The First Amendment extended the Company's option to draw down the second tranche of $8.5 million (the "Second Term Loan Advance") of the term loan facility provided under the Hercules Loan (the "Term Loan") until March 31, 2017, and made the Second Term Loan Advance subject to the consent of Hercules, among other customary conditions. The Second Amendment further extended the Company's option to draw the Second Term Loan Advance until January 31, 2018, and continues to make the Second Term Loan Advance subject to the consent of Hercules, among other customary conditions. The First Amendment also extended the interest-only payments until January 31, 2017, in connection with the first tranche of $16.5 million (the "First Term Loan Advance" and together with the Second Term Loan Advance, the "Term Loan Advances"). The Company is currently in discussions with Hercules to extend the period during which the additional tranche of $8.5 million may be drawn. The Company can make no assurances that its discussions will ultimately be successful and, if such discussions result in an extension of the periods in which the Company may draw the additional tranche of $8.5 million, the Company could incur additional fees to Hercules. The First Amendment provides the Term Loan will mature on December 1, 2018. As a result of the First Amendment, and in connection with the extension of the interest-only period from the First Term Loan Advance, Hercules returned to the Company the principal payments paid by the Company in July and August 2016, which such returned payments will once again constitute outstanding Term Loan advances under the Hercules Loan. In connection with the execution of the First Amendment, the Company paid Hercules a facility fee of $165. The facility fee represents a debt issue cost which is being reflected as a reduction to the carrying amount of loan payable in accordance with ASU 2015-03. Such issue costs are being amortized to interest expense over the life of the loan using the effective interest method. As of December 31, 2017, $10.9 million and $0 are recorded on the balance sheet in Loan payable, current portion and Loan payable, long-term, respectively. As of December 31, 2016, $5.6 million and $10.9 million are recorded on the balance sheet in Loan payable, current portion and Loan payable, long-term, respectively. As of December 31, 2017 and December 31, 2016, the Company had outstanding borrowings of $10.9 million and $16.5 million, respectively, related to the Hercules Loan. The Hercules Loan accrues interest at a rate of the greater of 9.0% or 9.0% plus Prime minus 4.25% and is payable monthly. Principal is due in 23 consecutive monthly installments beginning on February 1, 2017 and ending on December 1, 2018. In addition, the Company is required to make a final payment of approximately $611 on the maturity date of the Hercules Loan (December 1, 2018). The amount of the end of term final payment is being accrued over the loan term as interest expense. The Company may prepay all, but not less than all, of the Hercules Loan subject to a prepayment premium of 1.0% of the outstanding principal. The obligations of the Company under the Hercules Loan are secured by a perfected first position lien on all of the assets of the Company, excluding intellectual property assets. In connection with the Hercules Loan, the Company issued Hercules a warrant to purchase 180,274 shares of the Company's common stock at an exercise price of $5.89 per share which expires on February 24, 2020 and granted Hercules the right to participate in future equity financings in an amount up to $2.0 million while the loan and warrant are outstanding. The Company allocated the proceeds of $16.5 million in accordance with ASC 470 based on the relative fair values. The relative fair value of the warrants of approximately $1.2 million at the time of issuance, which was determined using the Black-Scholes option-pricing model, was recorded as additional paid-in capital and reduced the carrying value of the debt. The significant assumptions used in preparing the option pricing model for valuing the Company's warrant issued to Hercules include (i) volatility (75.0%), (ii) risk free interest rate of 1.22% (estimated using treasury bonds with a 4-year life), (iii) strike price ($5.89) for the common stock warrant, (iv) fair value of common stock ($9.82) and (v) expected life (4 years). The discount on the debt is being amortized to interest expense over the term of the debt. As a result of the repayment of the Oxford Loan, the Company recorded a loss on the extinguishment of debt of approximately $1.0 million on the Company's statement of operations for the year ended December 31, 2015, representing a prepayment premium, the unamortized discount of the Oxford Loan and the write off of deferred financing costs. Interest expense on the Oxford Loan and the Hercules Loan including the accretion of the value of the related warrants, accrual of term loan back-end fee and amortization of the deferred financing costs was approximately $1.9 million, $2.4 million and $2.1 million, for the years ended December 31, 2017, 2016 and 2015, respectively.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity
Stockholders' Equity	8. Stockholders' Equity The Company's Certificate of Incorporation, among other things: (i) authorizes 150,000,000 shares of common stock; (ii) authorizes 10,000,000 shares of undesignated preferred stock that may be issued from time to time by the Board in one or more series; (iii) provides that the Board be divided into three classes with staggered three-year terms, with one class of directors to be elected at each annual meeting of the Company's stockholders; (iv) provides that directors may only be removed with cause and only upon the affirmative vote of holders of at least 75% of the voting power of all then-outstanding shares of capital stock of the Company entitled to vote generally in the election of directors; (v) provides that only the Board, the chairman of the Board or the chief executive officer may call a special meeting of stockholders; and (vi) requires that any action instituted against the Company's officers or directors in connection with their service to the Company be brought in the State of Delaware. 2015 Private Placement of Common Stock In January 2015, the Company completed a private placement of approximately 3.4 million shares of common stock at $5.85 per share. Proceeds from the Company's private placement, net of commissions and other offering costs, were approximately $19.3 million. Two of the Company's stockholders, who are also affiliated with members of the Board, purchased a total of 1,623,932 shares of common stock for approximately $9.5 million in the private placement. Shelf Registration Statement On June 19, 2015, the Company filed a universal shelf registration statement with the Securities and Exchange Commission ("SEC") for the issuance of common stock, preferred stock, warrants, rights, debt securities and units up to an aggregate amount of $150.0 million (the "2015 Shelf Registration Statement"). On July 1, 2015, the 2015 Shelf Registration Statement was declared effective by the SEC. The Company completed an offering of common stock in both January 2016 and August 2017 utilizing the 2015 Shelf Registration Statement. In the future, the Company may also periodically offer one or more of these securities in amounts, prices and terms to be announced when and if the securities are offered. At the time any of the securities covered by the 2015 Shelf Registration Statement are offered for sale, a prospectus supplement will be prepared and filed with the SEC containing specific information about the terms of any such offering. 2016 Public Offering of Common Stock In January 2016, the Company completed an underwritten public offering of 5,511,812 shares of its common stock at a public offering price of $6.35 per share. In February 2016, the underwriters of the public offering of common stock exercised in full their option to purchase an additional 826,771 shares of common stock at the public offering price of $6.35 per share, less underwriting discounts and commissions. A total of 6,338,583 shares of common stock were sold in the public offering resulting in total net proceeds of approximately $37.5 million. One of the Company's stockholders, who is also affiliated with a member of the Board, purchased 393,700 shares of common stock for approximately $2.5 million in the public offering. 2017 Public Offering of Common Stock In August 2017, the Company completed an underwritten public offering of 5,333,334 shares of its common stock at a public offering price of $3.75 per share. Proceeds from this offering, net of underwriting discounts, commissions and other offering costs were approximately $18.5 million.

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2017
Equity Incentive Plans
Equity Incentive Plans	9. Equity Incentive Plans Stock options The Company had granted stock options under an amended and restated 1997 Equity Incentive Plan (the "1997 Plan") and a 2008 Equity Incentive Plan (the "2008 Plan"). The plans provided for the granting of incentive and non-statutory options and stock awards to consultants, directors, officers and employees. Such options are exercisable for a period of ten years and generally vest over a four-year period. In conjunction with the adoption of the 2008 Plan in April 2008, no additional grants were made from the 1997 Plan and issued options from the 1997 Plan remain outstanding. In 2014, the Board approved the 2014 Equity Incentive Plan (the "2014 Plan"). The 2014 Plan is the successor to the Company's 2008 Plan and 1997 Plan. In conjunction with the adoption of the 2014 Plan in 2014, no additional grants were made from the 2008 Plan and options from the 1997 Plan and the 2008 Plan remain outstanding. As of December 31, 2017, there were 211,141 shares available for future grant under the 2014 Plan. Through December 31, 2017, the Company granted options to certain employees and nonemployees to purchase shares of common stock at exercise prices ranging from $0.71 to $285.71 per share. The Company recorded noncash stock-based compensation expense for the years ended December 31, 2017, 2016 and 2015 based on the fair market value of the options and shares granted at the grant date. Stock-based compensation expense was as follows: Year Ended December 31, 2017 2016 2015 Research and development $ $ $ General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The following assumptions were used to compute employee stock-based compensation under the Black-Scholes option pricing model: 2017 2016 2015 Risk-free interest rate % % % Expected volatility % % % Expected dividend yield % % % Expected life (in years) Risk-free interest rate. The Company bases the risk-free interest rate assumption on observed interest rates appropriate for the expected term of the stock option grants. Expected dividend yield. The Company bases the expected dividend yield assumption on the fact that it has never paid cash dividends and has no present intention to pay cash dividends. Expected volatility. The expected volatility assumption is based on volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on comparable companies in the biotechnology and pharmaceutical industries. Expected term. The expected term represents the period of time that options are expected to be outstanding. Because the Company does not have historic exercise behavior, management determined the expected life assumption using the simplified method, which is an average of the contractual term of the option and its ordinary vesting period. Forfeitures. The Company has elected to record forfeitures as they occur. As of December 31, 2017, the unrecorded deferred stock-based compensation balance related to stock options was approximately $4.5 million and will be recognized over an estimated weighted-average amortization period of 1.62 years. The weighted average grant date fair value of options granted during the year ended December 31, 2017 was $1.75. The following table summarizes the options outstanding, options vested and the options exercisable as of December 31, 2017, 2016 and 2015: Options Weighted Weighted Average Aggregate Options outstanding at December 31, 2015 $ Options granted Options exercised ) Options cancelled/forfeited ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options outstanding at December 31, 2016 Options granted Options exercised ) Options cancelled/forfeited ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options outstanding at December 31, 2017 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options exercisable at December 31, 2017 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Vested and expected to vest at December 31, 2017 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Intrinsic value in the above table was calculated as the difference between the Company's stock price at December 31, 2017, of $2.69, and the exercise price, multiplied by the number of options. Intrinsic value for options exercised during 2017 amounts to approximately $159,000. Restricted stock In February 2016, the Company granted 50,000 RSUs to an employee of the Company, 16,666 RSUs vested on the grant date, 16,667 RSUs vested in February 2017 and the remaining 16,667 RSUs vested in February 2018. During the year ended December 31, 2017, the Company granted a total of 247,694 RSUs to executive officers and directors of the Company. These RSUs vest ratably over a two-year period for the executive officers and on the one-year anniversary of the grant date for the directors. The following table shows the Company's restricted stock activity during the years ended December 31, 2017, 2016 and 2015: Shares Weighted Average Aggregate Restricted stock outstanding at December 31, 2015 — $ — Granted Vested ) $ Cancelled/forfeited — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Restricted stock outstanding at December 31, 2016 Granted Vested ) $ Cancelled/forfeited — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Restricted stock outstanding at December 31, 2017 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ In addition to the RSUs detailed in the table above, during 2017 the Company granted up to 260,000 shares of performance-based restricted stock units ("Performance Units") under the Company's 2014 Incentive Compensation Plan, to executive officers which are primarily contingent upon achievement of performance goals during the performance period beginning on the date of grant and ending on December 31, 2018 as set forth in each officer's performance unit agreement. For awards with a performance condition which affects the vesting of the Performance Units, cost is recognized only if the performance condition is probable of being satisfied. Given the uncertainty of the achievement of the performance goals during the performance period, the Company has not recorded compensation expense related to these awards for the year ended December 31, 2017. These performance-based restricted stock units expired and were subsequently replaced with new awards in January 2018 (see Note 13).

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Taxes
Income Taxes	10. Income Taxes On December 22, 2017, the President of the United States signed into law an Act to provide for reconciliation pursuant to titles II and V of the concurrent resolution on the budget for fiscal year 2018 (commonly known as "the Tax Cuts and Jobs Act"), which introduced a comprehensive set of tax reforms. The Tax Cuts and Jobs Act significantly revises U.S. tax law by, among other provisions, lowering the Company's corporate tax rate from 34% to 21% and eliminating or reducing certain income tax deductions. The effects of changes in tax laws are required to be recognized in the period in which the legislation is enacted. However, due to the complexity and significance of the Tax Cuts and Jobs Act's provisions, the Company recorded the tax effects of the Tax Cuts and Jobs Act on a provisional basis based on a reasonable estimate, and will, if necessary, subsequently adjust such amounts during a limited measurement period as more information becomes available. The measurement period ends when a company has obtained, prepared, and analyzed the information necessary to finalize its accounting, but cannot extend beyond one year from enactment. The Tax Cuts and Jobs Act did not have a material impact on the Company's financial statements since its net deferred tax assets are fully offset by a valuation allowance and the Company does not have any off shore earnings from which to record the mandatory transition tax. However, given the significant complexity of the Tax Cuts and Jobs Act, anticipated guidance from the U.S. Treasury about implementing the Tax Cuts and Jobs Act, and the potential for additional guidance from the FASB related to the Tax Cuts and Jobs Act, these estimates may be adjusted during the measurement period. The provisional amounts were based on the Company's present interpretations of the Tax Cuts and Jobs Act and currently available information, including assumptions and expectations about future events, such as its projected financial performance, and are subject to further refinement as additional information becomes available (including the Company's actual results of operations for the year ending December 31, 2017, as well as potential new or interpretative guidance issued by the FASB or the Internal Revenue Service and other tax agencies) and further analyses are completed. The Company continues to analyze the changes in certain income tax deductions, and gather additional data to compute the full impacts on the Company's deferred and current tax assets and liabilities. As of December 31, 2017, the Company had available net operating loss carryforwards ("NOLs") of approximately $202.1 million and $68.8 million for federal and state income tax reporting purposes, respectively, which are available to offset future federal and state taxable income, if any, through 2037. The Company also has research and development tax credit carryforwards of approximately $5.4 million and $0.9 million for federal and state income tax reporting purposes, respectively, which are available to reduce federal and state income taxes, if any, through 2037 and state income taxes, if any, through 2032. The Internal Revenue Code of 1986, as amended (the "Code") provides for a limitation on the annual use of NOLs and other tax attributes (such as research and development tax credit carryforwards) following certain ownership changes, as defined by the Code that could significantly limit the Company's ability to utilize these carryforwards. At this time, the Company has not completed a study to assess whether an ownership change under Section 382 of the Code has occurred, or whether there have been multiple ownership changes since the Company's formation, due to the costs and complexities associated with such a study. The Company is likely to have experienced various ownership changes, as defined by the Code, as a result of past financings. Accordingly, the Company's ability to utilize the aforementioned carryforwards may be limited. Additionally, U.S. tax laws limit the time during which these carryforwards may be applied against future taxes. Therefore, the Company may not be able to take full advantage of these carryforwards for federal and state income tax purposes. The Company does not have any significant unrecognized tax benefits. As of December 31, 2017, the Company has not accrued interest or penalties related to uncertain tax positions. The Company's tax returns for the years ended December 31, 2014 through December 31, 2016 are still subject to examination by major tax jurisdictions. However, the Internal Revenue Service ("IRS") and state tax jurisdictions can audit the NOLs generated in prior years in the years that those NOLs are utilized. For all years through December 31, 2017, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company's research and development credit carryforwards; however, until a study is completed and any adjustment in known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company's research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance. The tax effects of temporary differences that give rise to significant portions of the deferred tax assets are presented below: December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ $ Research credit carryforward Stock options and other ​ ​ ​ ​ ​ ​ ​ ​ Total gross deferred tax assets Valuation allowance for deferred tax assets ) ) ​ ​ ​ ​ ​ ​ ​ ​ Net deferred tax assets $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The gross deferred tax assets and the valuation allowance shown above represent the items which reduce the income tax benefit which would result from applying the federal statutory tax rate to the pretax loss and cause no income tax expense or benefit to be recorded for the years ended December 31, 2017 and 2016. The net change in the valuation allowance for the years ended December 31, 2017 and 2016 was a decrease of $14.6 million and an increase of $10.4 million, respectively. The decrease in 2017 related primarily to the change in the Federal tax rate as discussed earlier under the Act. The increase in 2017 related primarily to net operating losses incurred by the Company which are not currently deductible. A reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate is as follows: December 31, 2017 2016 2015 Federal income tax at statutory rate % % % State income tax benefit, net of federal benefit % % % Research and development tax credits % % % Effect of tax rate changes –94.0 % % % Other –1.0 % % –2.0 % Decrease (increase) to valuation allowance % –33.0 % –24.0 % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Effective income tax rate % % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Sale of New Jersey Net Operating Losses The Company received approval to sell a portion of the Company's New Jersey NOLs as part of the Technology Business Tax Certificate Program sponsored by The New Jersey Economic Development Authority. Under the program, emerging biotechnology companies with unused NOLs and unused research and development credits are allowed to sell these benefits to other companies. In December 2016, the Company completed the sale of NOLs totaling approximately $28.2 million and research and development credits totaling approximately $0.8 million for net proceeds of approximately $3.0 million. Such proceeds are reflected as a tax benefit for the year ended December 31, 2016. On November 30, 2015, the Company completed the sale of NOLs totaling approximately $59.8 million and research and development credits totaling $1.1 million for net proceeds of approximately $6.0 million. Such proceeds are reflected as a tax benefit for the year ended December 31, 2015. On February 27, 2014, the Company completed the sale of NOLs totaling approximately $39.1 million and research and development credits totaling approximately $0.4 million for net proceeds of approximately $3.6 million. Such proceeds are reflected as a tax benefit for year ended December 31, 2014.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions
Related Party Transactions	11. Related Party Transactions Between March 17, 2014 and July 6, 2016, one of the Managing Partners of SmartPharma LLC ("SmartPharma"), an entity which provides commercial and business development consulting services to the Company, served as Chief Commercial Officer of the Company. In connection with the appointment of this individual as Chief Commercial Officer, the Company amended its consulting agreement with SmartPharma to remove this individual from the list of persons providing service under the consulting agreement. SmartPharma invoiced the Company approximately $0, $3 and $73 of fees for the years ended December 31, 2017, 2016 (through July 6, 2016) and 2015, respectively. In connection with the resignation of our Chief Commercial Officer who was affiliated with SmartPharma on July 6, 2016, the Company appointed a new Chief Commercial Officer.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies
Commitments and Contingencies	12. Commitments and Contingencies Operating Leases The Company leases approximately 8,200 square feet of office space in Princeton, NJ. The current term of the lease is for a five-year period ending on November 30, 2020. The Company has the right to terminate the lease after November 30, 2018 under certain circumstances as defined in the lease. Rent expense was approximately $193, $195 and $163 for the years ended December 31, 2017, 2016 and 2015, respectively. Future minimum annual lease commitments under the non-cancelable operating lease in effect as of December 31, 2017 are as follows: 2018 $ 2019 2020 2021 — 2022 — ​ ​ ​ ​ ​ Total $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Legal Proceedings On January 6, 2017, and January 20, 2017, two previously disclosed complaints captioned Peng v. Agile Therapeutics, Inc., Alfred Altomari, and Elizabeth Garner, No. 17-cv-119 (D.N.J.), and Lichtenthal v. Agile Therapeutics, Inc., Alfred Altomari, and Elizabeth Garner, No. 17-cv-405 (D.N.J.), respectively, were filed in the United States District Court for the District of New Jersey on behalf of a putative class of investors who purchased shares of the Company's common stock from March 9, 2016, through January 3, 2017. The complaints alleged violations of the federal securities laws based on public statements made regarding the Company's Phase 3 SECURE clinical trial and sought an unspecified amount of damages to be determined at trial. The Company denied all allegations in the complaints. On May 15, 2017, the complaints were consolidated the lawsuits as In re Agile Therapeutics, Inc. Securities Litigation, Master File No. 17-cv-119 (D.N.J.), and Hoyt W. Clark was appointed as a class representative for the putative class. On June 26, 2017, Mr. Clark agreed to dismiss the consolidated case voluntarily, without payment by the Company of any consideration and with each side bearing its own attorneys' fees and costs. The presiding judge dismissed the consolidated action with prejudice as to all defendants on July 13, 2017. The Company records a provision for contingent losses when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. An unfavorable outcome to any legal matter, if material, could have an adverse effect on the Company's operations or its financial position. As of December 31, 2017, the Company has not recorded a provision for any contingent losses.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events
Subsequent Events	13. Subsequent Events Sale of New Jersey Net Operating Losses In January 2018, the Company received net proceeds of approximately $0.5 million in non-dilutive financing through the State of New Jersey's Technology Business Tax Certificate Transfer Program (the "Program"). The Program enables approved biotechnology companies to sell their unused Net Operating Loss Carryovers and unused Research and Development Tax Credits for at least 80% of the value of the tax benefits to unaffiliated, profitable corporate taxpayers in the State of New Jersey. The New Jersey Economic Development Authority and the New Jersey Department of the Treasury's Division of Taxation administer the Program. The Company intends to use the proceeds from the sale for working capital purposes. The Company has now reached the maximum lifetime benefit of $15.0 million under the Program and will no longer be eligible to participate in the Program. Performance Based Restricted Stock Awards In January 2018, the Company granted up to 365,000 shares of performance-based restricted stock units ("Performance Units") under the Company's 2014 Incentive Compensation Plan primarily to executive officers which are largely contingent upon the achievement of performance goals during the performance period beginning on the date of grant and ending on December 31, 2019 as set forth in each individual's performance unit agreement. Performance Units granted in January 2018 replaced Performance Units granted in April 2017 which expired.

Quarterly Data (Unaudited)

Quarterly Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Data (Unaudited)
Quarterly Data (Unaudited)	14. Quarterly Data (Unaudited) The following tables summarize the quarterly results of operations for each of the quarters in 2017 and 2016. These quarterly results are unaudited, but in the opinion of management, have been prepared on the same basis as our audited financial information and include all adjustments (consisting only of normal recurring adjustments) necessary for a fair presentation of the information set forth herein (in thousands, except per share amounts). March 31, June 30, September 30, December 31, Total revenue $ — $ — $ — $ — Operating expenses $ $ $ $ Net loss $ ) $ ) $ ) $ ) Basic and diluted net loss per common share $ ) $ ) $ ) $ ) March 31, June 30, September 30, December 31, Total revenue $ — $ — $ — $ — Operating expenses $ $ $ $ Net loss $ ) $ ) $ ) $ ) Basic and diluted net loss per common share $ ) $ ) $ ) $ ) The net loss and basic and diluted net loss per share for the quarters ended December 31, 2017 and 2016 include a tax benefit of $0 and $3.1 million, respectively, from the sale of New Jersey state NOLs. (see Note 10).

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in accordance with United States generally accepted accounting principles ("U.S. GAAP") and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented. Certain prior period amounts have been reclassified to conform to the current period presentation.
Use of Estimates	Use of Estimates The preparation of the Company's financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company bases its estimates and judgments on historical experience and various other assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company's balance sheets and the amounts of expenses reported for each of the periods presented are affected by estimates and assumptions, which are used for, but not limited to, the accounting for common stock warrants, stock-based compensation, income taxes, and accounting for research and development costs. Actual results could differ from those estimates.
Risks and Uncertainties	Risks and Uncertainties Product candidates developed by the Company typically will require approval from the FDA prior to commercial sales. There can be no assurance that the Company's product candidates will receive the required approval. If the Company was denied approval or such approval was delayed, or is unable to obtain the necessary financing to complete development and approval, there will be a material adverse impact on the Company's financial condition and results of operations.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly-liquid investments with an original maturity of three months or less when purchased to be cash equivalents. All cash and cash equivalents are held in United States financial institutions. Cash and cash equivalents include money market funds that invest primarily in commercial paper and U.S. government and U.S. government agency obligations. The Company maintains balances with financial institutions in excess of the Federal Deposit Insurance Corporation limit.
Fair Value of Financial Instruments	Fair Value of Financial Instruments In accordance with Accounting Standards Codification ("ASC") 825, Financial Instruments , disclosures of fair value information about financial instruments are required, whether or not recognized in the balance sheet, for which it is practicable to estimate that value. Cash and cash equivalents are carried at fair value (see Note 3). Financial instruments, including accounts payable and accrued liabilities, are carried at cost, which approximates fair value given their short-term nature.
Property and Equipment	Property and Equipment Property and equipment, consisting of manufacturing, office and computer equipment, is stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line, method over the estimated useful lives of the assets. Expenditures incurred after the fixed assets have been put into operation, such as repairs and maintenance, are charged to earnings in the period in which costs are incurred. Improvements and additions are capitalized in accordance with Company policy.
Long-Lived Assets	Long-Lived Assets In accordance with ASC 360, Property, Plant and Equipment , the Company's policy is to review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Management does not believe that there has been any impairment of the carrying value of any long-lived assets as of December 31, 2017.
Research and Development Expense	Research and Development Expense Research and development costs are expensed as incurred. Research and development expense consists primarily of costs related to personnel, including salaries and other personnel-related expenses, expenses related to manufacturing, clinical trial expenses, consulting fees and support services used in drug development. All research and development costs are charged to operations as incurred in accordance with ASC 730, Research and Development . In certain circumstances, the Company is required to make advance payments to vendors for goods or services that will be received in the future for use in research and development activities. In such circumstances, the advance payments are deferred and are expensed when the activity has been performed or when the goods have been received.
Deferred Financing Costs	Deferred Financing Costs Costs directly attributable to the Company's term loan (see Note 7) are deferred and reported as a reduction of the related term loan. These costs represent legal fees and other costs related to the term loan and are being amortized over the term of the loan. Amortization of deferred financing costs charged to interest expense was approximately $239, $256 and $211 for the years ended December 31, 2017, 2016 and 2015, respectively.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments which potentially subject the Company to credit risk consist principally of cash and cash equivalents. All cash and cash equivalents are held in business checking and money market accounts in United States financial institutions the balances of which exceed federally insured limits. The Company has not recognized any losses from credit risks on such accounts. The Company believes it is not exposed to significant credit risks on cash and cash equivalents. The Company has no financial instruments with off-balance sheet risk of accounting loss.
Warrants	Warrants The Company accounts for its warrants to purchase redeemable convertible stock in accordance with ASC 480, Distinguishing Liabilities from Equity . ASC 480 requires that a financial instrument, other than outstanding share, that, at inception, is indexed to an obligation to repurchase the issuer's equity shares, regardless of the timing or the probability of the redemption feature, and may require the issuer to settle the obligation by transferring assets be classified as a liability. The Company measures the fair value of its warrant liability using the Black-Scholes option pricing model with changes in fair value recognized as increases or reductions to other income (expense) in the statement of operations. In connection with the completion of the Company's initial public offering in May 2014, the warrants to purchase shares of Series A-1 and Series A-2 preferred stock expired unexercised and the warrants to purchase shares of Series C preferred stock automatically converted into warrants to purchase shares of common stock. Warrants with non-standard anti-dilution provisions (referred to as down round protection) are classified as liabilities and re-measured each reporting period. As of December 31, 2017, there were outstanding 62,505 warrants to purchase common stock at $6.00 per share. These warrants expire on December 14, 2019. The warrants issued in connection with the Company's debt financing completed in February 2015 (see Note 7) are classified as a component of stockholders' equity. The value of such warrants was determined using the Black-Scholes option-pricing model. As of December 31, 2017, there were outstanding 180,274 warrants to purchase common stock at $5.89 per share related to this debt financing. These warrants expire on February 24, 2020.
Income Taxes	Income Taxes The Company accounts for deferred taxes using the asset and liability method as specified by ASC 740, Income Taxes . Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and the tax basis of assets and liabilities, operating losses and tax credit carryforwards. Deferred income taxes are measured using the enacted tax rates and laws that are anticipated to be in effect when the differences are expected to reverse. The measurement of deferred income tax assets is reduced, if necessary, by a valuation allowance for any tax benefits which are not expected to be realized. The effect on deferred income tax assets and liabilities of a change in tax rates is recognized in the period that such tax rate changes are enacted. The Company has adopted the authoritative guidance on accounting for and disclosure of uncertainty in tax positions which prescribes a comprehensive model for the financial statement recognition, measurement, presentation and disclosure of uncertain tax positions taken or expected to be taken in income tax returns. The Company has no uncertain tax positions as of December 31, 2017 that qualifies for either recognition or disclosure in the financial statements under this guidance.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation in accordance with ASC 718, Compensation—Stock Compensation . The Company grants stock options for a fixed number of shares to employees and non-employees with an exercise price equal to the fair value of the shares at grant date. Compensation cost is recognized for all share-based payments granted and is based on the grant-date fair value estimated using the weighted-average assumption of the Black-Scholes option pricing model based on key assumptions such as stock price, expected volatility and expected term. The Company elects to account for forfeitures when they occur. The equity instrument is not considered to be issued until the instrument vests. As a result, compensation cost is recognized over the requisite service period with an offsetting credit to additional paid-in capital. The Company also awards restricted stock units ("RSUs") to employees and its board of directors (the "Board"). RSUs are generally subject to forfeiture if employment terminates prior to the completion of the vesting restrictions. The Company expenses the cost of the RSUs, which is determined to be the fair market value of the shares of common stock underlying the RSUs at the date of grant, ratably over the period during which the vesting restrictions lapse. Cost associated with performance-based restricted stock units with a performance condition which affects the vesting is recognized only if the performance condition is probable of being satisfied. Awards for consultants are accounted for under ASC 505-50, Equity Based Payments to Non-Employees . Any compensation expense related to consultants is marked-to-market over the applicable vesting period as they vest. Prior to May 22, 2014, the Company utilized various methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation , to estimate the fair value of its stock. The methodologies included an option pricing method and a probability-weighted expected return methodology that determined an estimated value under an initial public offering ("IPO") scenario and a sale scenario based upon an assessment of the probability of occurrence of each scenario. Each valuation methodology includes estimates and assumptions that require the Company's judgment. These estimates include assumptions regarding future performance, including the successful completion of clinical trials and the time to completing an IPO or sale of the Company. As with any valuation, significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating and reporting segment, which is the business of developing its transdermal patch for use in contraception.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding plus the effect of dilutive potential common shares outstanding during the period determined using the treasury-stock and if-converted methods. For purposes of diluted net loss per share calculation, common stock warrants, unvested RSUs and stock options are considered to be potentially dilutive securities but are excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive and therefore, basic and diluted net loss per share were the same for all periods presented. The following table sets forth the outstanding potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because to do so would be anti-dilutive (in common equivalent shares): Year Ended December 31, 2017 2016 2015 Common stock warrants Unvested restricted stock units — Common stock options ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board ("FASB") or other standard setting bodies that the Company adopts as of the specified effective date. Unless otherwise discussed below, the Company does not believe that the adoption of recently issued standards have or may have a material impact on our consolidated financial statements or disclosures. In May 2014, as part of its ongoing efforts to assist in the convergence of U.S. GAAP and International Financial Reporting Standards, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which is a new standard related to revenue recognition. Under the new standard, recognition of revenue occurs when a customer obtains control of promised services or goods in an amount that reflects the consideration to which the entity expects to receive in exchange for those goods or services. In addition, the standard requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from customer contracts. The standard must be adopted using either a full retrospective approach for all periods presented in the period of adoption or a modified retrospective approach. In July 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers—Deferral of the Effective Date , which defers the implementation of this new standard to be effective for fiscal years beginning after December 15, 2017. Early adoption is permitted effective January 1, 2017. In March 2016, the FASB issued ASU 2016-08, Principal versus Agent Considerations , which clarifies the implementation guidance on principal versus agent considerations in the new revenue recognition standard pursuant to ASU 2014-09. In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing , and in May 2016, the FASB issued ASU 2016-12, Narrow-Scope Improvements and Practical Expedients , which amend certain aspects of the new revenue recognition standard pursuant to ASU 2014-09. In December 2016, the FASB issued ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers to clarify the codification or to correct unintended application of guidance. In September and November 2017, the FASB issued ASU 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842) and ASU 2017-14, Income Statement—Reporting Comprehensive Income (Topic 220), Revenue Recognition (Topic 605), and Revenue from Contracts with Customers (Topic 606) which amends certain aspects of the new revenue recognition standard. As the Company has not recognized any revenue to date, the adoption did not have any impact on the Company's financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases . The new standard establishes a right-of-use ("ROU") model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the statement of operations. The new standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. A modified retrospective transition approach is required for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. In September 2017, the FASB issued ASU 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842) which amends certain aspects of the new lease standard. The Company is currently evaluating the impact of the pending adoption of the new standard on the Company's financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting to provide clarity and reduce both (1) diversity in practice and (2) cost and complexity when applying the guidance in Topic 718, Compensation—Stock Compensation , to change the terms or conditions of a share-based payment award. The amendments in this Update provide guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. This Update is the final version of Proposed ASU 2016-360 —Compensation—Stock Compensation (Topic 718)—Scope of Modification Accounting , which has been deleted. The amendments in this Update are effective for all entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted. This ASU is not expected to have a material impact on the Company's financial statements. In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part 1) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception." This ASU eliminates the requirement to consider "down round" features when determining whether certain equity-linked financial instruments or embedded features are indexed to an entity's own stock. ASU 2017-11 is effective for annual periods beginning after December 31, 2018. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of ASU 2017-11 on its financial statements. Management does not believe that any other recently issued, but not yet effective accounting pronouncements, if adopted, would have a material impact on the accompanying consolidated financial statements.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Significant Accounting Policies
Schedule of outstanding potentially dilutive securities excluded from calculation of diluted net loss per share	The following table sets forth the outstanding potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because to do so would be anti-dilutive (in common equivalent shares): Year Ended December 31, 2017 2016 2015 Common stock warrants Unvested restricted stock units — Common stock options ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Measurements
Schedule of financial instruments measured at fair value by level within the fair value hierarchy	Level 1 Level 2 Level 3 2017 Assets: Cash equivalents $ $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total assets at fair value $ $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities: Common stock warrants $ — $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total liabilities at fair value $ — $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Level 1 Level 2 Level 3 2016 Assets: Cash equivalents $ $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total assets at fair value $ $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities: Common stock warrants $ — $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total liabilities at fair value $ — $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of roll forward of the fair value of Level 3 warrants	Beginning balance at December 31, 2014 $ Change in fair value ​ ​ ​ ​ ​ Ending balance at December 31, 2015 Change in fair value ) ​ ​ ​ ​ ​ Ending balance at December 31, 2016 Change in fair value ) ​ ​ ​ ​ ​ Ending balance at December 31, 2017 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Prepaid Expenses (Tables)

Prepaid Expenses (Tables)	12 Months Ended
	Dec. 31, 2017
Prepaid Expenses
Schedule of prepaid expenses	December 31, 2017 2016 Prepaid clinical trial expense $ $ Prepaid insurance Other ​ ​ ​ ​ ​ ​ ​ ​ Total prepaid expenses $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property and Equipment
Schedule of components of property and equipment	December 31, 2017 2016 Estimated Life Office equipment $ $ 3 - 10 years Computer equipment 3 years Manufacturing equipment 5 years ​ ​ ​ ​ ​ ​ ​ ​ ​ Less: accumulated depreciation ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ Property and equipment $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Accrued Liabilities
Schedule of accrued liabilities	December 31, 2017 2016 Employee bonuses $ $ Accrued clinical trial costs — Accrued interest payable Accrued professional fees and other ​ ​ ​ ​ ​ ​ ​ ​ Total accrued liabilities $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Equity Incentive Plans
Schedule of stock-based compensation expense	Year Ended December 31, 2017 2016 2015 Research and development $ $ $ General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of assumptions used to compute employee stock-based compensation	2017 2016 2015 Risk-free interest rate % % % Expected volatility % % % Expected dividend yield % % % Expected life (in years)
Summary of options outstanding, vested and exercisable	Options Weighted Weighted Average Aggregate Options outstanding at December 31, 2015 $ Options granted Options exercised ) Options cancelled/forfeited ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options outstanding at December 31, 2016 Options granted Options exercised ) Options cancelled/forfeited ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options outstanding at December 31, 2017 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options exercisable at December 31, 2017 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Vested and expected to vest at December 31, 2017 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of restricted stock activity	Shares Weighted Average Aggregate Restricted stock outstanding at December 31, 2015 — $ — Granted Vested ) $ Cancelled/forfeited — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Restricted stock outstanding at December 31, 2016 Granted Vested ) $ Cancelled/forfeited — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Restricted stock outstanding at December 31, 2017 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Taxes
Schedule of tax effects of temporary differences that give rise to significant portions of deferred tax assets	December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ $ Research credit carryforward Stock options and other ​ ​ ​ ​ ​ ​ ​ ​ Total gross deferred tax assets Valuation allowance for deferred tax assets ) ) ​ ​ ​ ​ ​ ​ ​ ​ Net deferred tax assets $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of reconciliation of U.S. statutory income tax rate to effective tax rate	December 31, 2017 2016 2015 Federal income tax at statutory rate % % % State income tax benefit, net of federal benefit % % % Research and development tax credits % % % Effect of tax rate changes –94.0 % % % Other –1.0 % % –2.0 % Decrease (increase) to valuation allowance % –33.0 % –24.0 % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Effective income tax rate % % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies
Schedule of future minimum annual lease commitments under non-cancelable operating lease	2018 $ 2019 2020 2021 — 2022 — ​ ​ ​ ​ ​ Total $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Quarterly Data (Unaudited) (Tab

Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Data (Unaudited)
Summary of quarterly results of operations	March 31, June 30, September 30, December 31, Total revenue $ — $ — $ — $ — Operating expenses $ $ $ $ Net loss $ ) $ ) $ ) $ ) Basic and diluted net loss per common share $ ) $ ) $ ) $ ) March 31, June 30, September 30, December 31, Total revenue $ — $ — $ — $ — Operating expenses $ $ $ $ Net loss $ ) $ ) $ ) $ ) Basic and diluted net loss per common share $ ) $ ) $ ) $ )

Organization and Description 31

Organization and Description of Business (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Organization and Description of Business
Product revenue	$ 0
Accumulated deficit	(221,772)	$ (193,468)
Cash and cash equivalents	$ 35,952	$ 48,750	$ 34,395	$ 40,182

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Deferred Financing Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest expense
Deferred Financing Costs
Amortization of deferred financing costs	$ 239	$ 256	$ 211

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Concentrations of Credit Risk (Details) $ in Thousands	Dec. 31, 2017USD ($)
Concentration of risk, financial assets
Financial instruments with off-balance sheet risk of accounting loss, assets	$ 0
Concentration risk, financial liabilities
Financial instruments with off-balance sheet risk of accounting loss, liabilities	$ 0

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Warrants (Details) - Common stock warrants - $ / shares	Dec. 31, 2017	Feb. 28, 2015	Dec. 31, 2012
Warrants | Oxford Finance LLC
Warrants
Common stock that can be purchased with warrants (in shares)	62,505		62,505
Exercise price of warrants (in dollars per share)	$ 6		$ 6
Warrants | Hercules Capital, Inc.
Warrants
Common stock that can be purchased with warrants (in shares)	180,274	180,274
Exercise price of warrants (in dollars per share)	$ 5.89	$ 5.89

Summary of Significant Accoun35

Summary of Significant Accounting Policies - Income Taxes (Details) $ in Thousands	Dec. 31, 2017USD ($)
Uncertainty in tax positions
Uncertain tax positions	$ 0

Summary of Significant Accoun36

Summary of Significant Accounting Policies - Segment Information (Details)	12 Months Ended
	Dec. 31, 2017segment
Segment Information
Number of operating segments	1
Number of reporting segments	1

Summary of Significant Accoun37

Summary of Significant Accounting Policies - Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	4,312,445	3,121,083	2,407,844
Common stock warrants
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	242,779	242,779	242,779
Restricted stock units
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	264,361	33,334
Common stock options
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	3,805,305	2,844,970	2,165,065

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments Measured at Fair Value by Hierarchy Level and Significant Assumptions Used for Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Liabilities:
Common stock warrants	$ 29	$ 172
Recurring | Level 1
Assets:
Total assets at fair value	35,870	48,659
Recurring | Level 1 | Cash equivalents
Assets:
Cash equivalents	35,870	48,659
Recurring | Level 3
Liabilities:
Total liabilities at fair value	29	172
Recurring | Level 3 | Warrants | Common stock warrants
Liabilities:
Common stock warrants	$ 29	$ 172
Recurring | Level 3 | Warrants | Common stock warrants | Option pricing model
Significant assumptions used in preparing the option pricing model for valuing the Company's warrants
Volatility (as a percent)	70.00%	75.00%
Risk free interest rate (as a percent)	1.89%	1.47%
Life of treasury bonds	2 years	3 years
Strike price (in dollars per share)	$ 6	$ 6
Fair value of common stock (in dollars per share)	$ 2.69	$ 5.70
Expected life (in years)	2 years	3 years

Fair Value Measurements - Roll

Fair Value Measurements - Roll forward of Fair Value of Level 3 Warrants and Transfers Between Levels (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair value measurements
Asset transfers out of Level 1 into Level 2	$ 0	$ 0
Asset transfers out of Level 2 into Level 1	0	0
Asset transfers into (out of) Level 3	0	0
Liability transfers out of Level 1 into Level 2	0	0
Liability transfers out of Level 2 into Level 1	0	0
Liability transfers into (out of) Level 3	0	0
Warrants | Liabilities
Rollforward of the fair value of Level 3 warrants:
Beginning balance	172	406	$ 296
Change in fair value	(143)	(234)	110
Ending balance	$ 29	$ 172	$ 406

Prepaid Expenses (Details)

Prepaid Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expenses
Prepaid clinical trial expense	$ 205	$ 2,005
Prepaid insurance	388	665
Other	169	98
Total prepaid expenses	$ 762	$ 2,768

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Property and equipment, gross	$ 14,209	$ 12,653
Less: accumulated depreciation	(346)	(323)
Property and equipment, net	13,863	12,330
Office equipment
Property and Equipment
Property and equipment, gross	$ 49	$ 55
Office equipment | Minimum
Property and Equipment
Estimated Life (in years)	3 years	3 years
Office equipment | Maximum
Property and Equipment
Estimated Life (in years)	10 years	10 years
Computer equipment
Property and Equipment
Property and equipment, gross	$ 175	$ 133
Estimated Life (in years)	3 years	3 years
Manufacturing equipment
Property and Equipment
Property and equipment, gross	$ 13,985	$ 12,465
Estimated Life (in years)	5 years	5 years
Manufacturing equipment in process of being constructed and qualified
Property and Equipment
Property and equipment, gross	$ 13,800	$ 12,400

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities
Employee bonuses	$ 215	$ 1,041
Accrued clinical trial costs		1,908
Accrued interest payable	451	292
Accrued professional fees and other	186	403
Total accrued liabilities	$ 852	$ 3,644

Loan and Security Agreements -

Loan and Security Agreements - Oxford Loan and Hercules Loan (Details) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 28, 2015USD ($)$ / sharesshares	Dec. 31, 2012USD ($)installment$ / sharesshares	Dec. 31, 2017USD ($)installment$ / sharesshares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Aug. 31, 2016USD ($)
Loan and Security Agreements
Loan payable, current portion			$ 10,607	$ 5,104
Loan payable, long-term				10,607
Fair value of common stock warrants issued with debt financing					$ 1,184
Loss on extinguishment of debt					1,036
Oxford Loan | Oxford Finance LLC | Secured debt
Loan and Security Agreements
Loss on extinguishment of debt					1,000
Hercules Loan | Hercules Capital, Inc. | Equity financings | Right to participate in future equity financings | Maximum
Loan and Security Agreements
Equity financings amount	$ 2,000
Warrants | Common stock warrants | Hercules Capital, Inc.
Loan and Security Agreements
Common stock that can be purchased with warrants (in shares) | shares	180,274		180,274
Exercise price of warrants (in dollars per share) | $ / shares	$ 5.89		$ 5.89
Significant assumptions used in preparing the option pricing model for valuing the Company's warrants
Volatility (as a percent)	75.00%
Risk free interest rate (as a percent)	1.22%
Life of treasury bonds	4 years
Strike price (in dollars per share) | $ / shares	$ 5.89
Fair value of common stock (in dollars per share) | $ / shares	$ 9.82
Expected life (in years)	4 years
Additional Paid-in Capital
Loan and Security Agreements
Fair value of common stock warrants issued with debt financing					1,184
Additional Paid-in Capital | Hercules Capital, Inc.
Loan and Security Agreements
Fair value of common stock warrants issued with debt financing	$ 1,200
Warrants | Common stock warrants | Oxford Finance LLC
Loan and Security Agreements
Common stock that can be purchased with warrants (in shares) | shares		62,505	62,505
Exercise price of warrants (in dollars per share) | $ / shares		$ 6	$ 6
Secured debt
Loan and Security Agreements
Interest expense, including accretion of value of related warrants and amortization of deferred financing costs			$ 1,900	2,400	$ 2,100
Secured debt | Oxford Loan | Oxford Finance LLC
Loan and Security Agreements
Amount borrowed		$ 15,000
Fixed interest rate (as a percent)		9.20%
Number of consecutive monthly principal installments | installment		30
Final payment amount due		$ 675
Repayment of existing debt	15,500
Secured debt | Hercules Loan | Hercules Capital, Inc.
Loan and Security Agreements
Maximum borrowing capacity	25,000
Facility Fee						$ 165
Loan payable, current portion			10,900	5,600
Loan payable, long-term			0	10,900
Outstanding borrowings			$ 10,900	$ 16,500
Fixed interest rate (as a percent)			9.00%
Number of consecutive monthly principal installments | installment			23
Final payment amount due			$ 611
Prepayment premium as percentage of outstanding principal			1.00%
Discount on debt	1,200
Secured debt | Hercules Loan Tranche One | Hercules Capital, Inc.
Loan and Security Agreements
Amount borrowed	$ 16,500
Secured debt | Hercules Loan Tranche Two | Hercules Capital, Inc.
Loan and Security Agreements
Additional amount available			$ 8,500
Secured debt | LIBOR | Oxford Loan | Oxford Finance LLC
Loan and Security Agreements
Variable rate basis		Three-month U.S. Libor
Reference rate (as a percent)		0.47%
Variable interest rate margin (as a percent)		8.73%
Secured debt | Prime | Hercules Loan | Hercules Capital, Inc.
Loan and Security Agreements
Variable rate basis			Prime minus 4.25%
Variable interest rate margin (as a percent)			9.00%
Variable rate adjustment (as a percent)			(4.25%)

Stockholders' Equity - Amended

Stockholders' Equity - Amended and Restated Certificate of Incorporation (Details)	12 Months Ended
	Dec. 31, 2017classshares	Dec. 31, 2016shares
Stockholders' Equity
Common stock, authorized (in shares) | shares	150,000,000	150,000,000
Preferred stock, authorized (in shares) | shares	10,000,000
Board of Directors, number of classes | class	3
Term of Board member	3 years
Number of classes elected at each annual meeting | class	1
Minimum
Stockholders' Equity
Affirmative vote of all then-outstanding shares of capital stock for removal of directors (as a percent)	75.00%

Stockholders' Equity - Private

Stockholders' Equity - Private Placement (Details) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2015USD ($)shareholder$ / sharesshares	Dec. 31, 2015USD ($)shares
Stockholders' Equity
Proceeds from issuance of stock		$ 19,330
Private Placement | Stockholders affiliated with members of board of directors
Stockholders' Equity
Number of stockholders affiliated with members of board of directors who purchased shares | shareholder	2
Private Placement | Common Stock
Stockholders' Equity
Shares issued (in shares) | shares	3,400,000	3,418,804
Share price (in dollars per share) | $ / shares	$ 5.85
Proceeds from issuance of stock	$ 19,300
Private Placement | Common Stock | Stockholders affiliated with members of board of directors
Stockholders' Equity
Shares issued (in shares) | shares	1,623,932
Proceeds from issuance of stock	$ 9,500

Stockholders' Equity - Shelf Re

Stockholders' Equity - Shelf Registration Statement (Details) $ in Millions	Jun. 19, 2015USD ($)
2015 Shelf Registration
Sale of stock
Aggregate amount of securities issuable	$ 150

Stockholders' Equity - 2016 & 2

Stockholders' Equity - 2016 & 2017 Public Offerings of Common Stock (Details) $ / shares in Units, $ in Thousands	1 Months Ended			2 Months Ended	12 Months Ended
	Aug. 31, 2017USD ($)$ / sharesshares	Feb. 29, 2016$ / sharesshares	Jan. 31, 2016USD ($)shareholder$ / sharesshares	Feb. 29, 2016USD ($)$ / sharesshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Sale of stock
Proceeds from the issuance of common stock, net | $					$ 18,535	$ 37,528
2016 Public Offering | Stockholders affiliated with members of board of directors
Sale of stock
Number of stockholders affiliated with members of board of directors who purchased shares | shareholder			1
2016 Public Offering | Common Stock
Sale of stock
Shares issued (in shares) | shares			5,511,812	6,338,583
Share price (in dollars per share) | $ / shares			$ 6.35
Proceeds from the issuance of common stock, net | $				$ 37,500
2016 Public Offering | Common Stock | Stockholders affiliated with members of board of directors
Sale of stock
Shares issued (in shares) | shares			393,700
Proceeds from the issuance of common stock, net | $			$ 2,500
Underwriter purchase option | Common Stock
Sale of stock
Shares issued (in shares) | shares		826,771
Share price (in dollars per share) | $ / shares		$ 6.35		$ 6.35
2017 Public Offering | Common Stock
Sale of stock
Shares issued (in shares) | shares	5,333,334
Share price (in dollars per share) | $ / shares	$ 3.75
Proceeds from the issuance of common stock, net | $	$ 18,500

Equity Incentive Plans -Stock O

Equity Incentive Plans -Stock Options Summary (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Incentive Plans
Total stock-based compensation expense	$ 3,651	$ 3,425	$ 2,965
Common stock options
Equity Incentive Plans
Total stock-based compensation expense	$ 3,651	3,425	2,965
Common stock options | Minimum
Equity Incentive Plans
Exercise prices of options granted through the end of the year (in dollars per share)	$ 0.71
Common stock options | Maximum
Equity Incentive Plans
Exercise prices of options granted through the end of the year (in dollars per share)	$ 285.71
Common stock options | Research and development
Equity Incentive Plans
Total stock-based compensation expense	$ 1,184	1,063	1,161
Common stock options | General and administrative
Equity Incentive Plans
Total stock-based compensation expense	$ 2,467	$ 2,362	$ 1,804
Common stock options | 1997 Plan and 2008 Plan
Equity Incentive Plans
Expiration period	10 years
Vesting period	4 years
Common stock options | 2014 Equity Incentive Plan
Equity Incentive Plans
Shares available for grant	211,141

Equity Incentive Plans - Assump

Equity Incentive Plans - Assumptions Used to Compute Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common stock options
Unrecorded deferred stock-based compensation
Unrecorded deferred stock-based compensation balance related to stock options	$ 4.5
Weighted-average amortization period over which cost is expected to be recognized	1 year 7 months 13 days
Weighted average grant date fair value of options granted (in dollars per share)	$ 1.75
Employee stock options
Assumptions used to compute employee stock based compensation under the Black-Scholes option pricing model
Risk-free interest rate (as a percent)	2.27%	1.48%	1.92%
Expected volatility (as a percent)	73.90%	75.00%	75.00%
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%
Expected life (in years)	6 years 3 months	6 years 3 months	6 years 3 months

Equity Incentive Plans - Stock

Equity Incentive Plans - Stock Option Activity (Details) - Common stock options - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Options
Options outstanding at beginning of year (in shares)	2,844,970	2,165,065
Options granted (in shares)	1,145,750	825,500
Options exercised (in shares)	(76,610)	(88,870)
Options cancelled/forfeited (in shares)	(108,805)	(56,725)
Options outstanding at end of year (in shares)	3,805,305	2,844,970
Options exercisable at end of year (in shares)	2,054,538
Vested and expected to vest at end of year (in shares)	3,805,305
Weighted Average Exercise Price
Options outstanding at beginning of year (in dollars per share)	$ 6.97	$ 7.19
Options granted (in dollars per share)	2.64	6.31
Options exercised (in dollars per share)	1.98	3.76
Options cancelled/forfeited (in dollars per share)	7.62	10.90
Options outstanding at end of year (in dollars per share)	5.74	$ 6.97
Options exercisable at end of year (in dollars per share)	6.98
Vested and expected to vest at end of year (in dollars per share)	$ 5.74
Weighted Average Remaining Contractual Life (Years)
Options outstanding at end of year	7 years 4 months 24 days	7 years 6 months
Options exercisable at end of year	6 years 2 months 12 days
Vested and expected to vest at end of year	7 years 4 months 24 days
Aggregate Intrinsic Value
Options outstanding at the end of the period (in dollars)	$ 612,000
Options exercisable at the end of the period (in dollars)	228,000
Vested and expected to vest at end of year	$ 612,000
Estimated stock price (in dollars per share)	$ 2.69
Options exercised during the year, intrinsic value	$ 159,000

Equity Incentive Plans - Restri

Equity Incentive Plans - Restricted Stock (Details) - Restricted stock units - USD ($)	1 Months Ended			12 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 29, 2016	Dec. 31, 2017	Dec. 31, 2016
Shares
Restricted stock outstanding at beginning of year (in shares)				33,334	0
Granted (in shares)				247,694	50,000
Vested (in shares)				(16,667)	(16,666)
Restricted stock outstanding at end of year (in shares)				264,361	33,334
Weighted Average Grant Date Fair Value
Restricted stock outstanding at beginning of year (in dollars per share)				$ 5.93	$ 0
Granted (in dollars per share)				2.97	5.93
Vested (in dollars per share)				5.93	5.93
Restricted stock outstanding at end of year (in dollars per share)				$ 3.16	$ 5.93
Aggregate Intrinsic Value
Intrinsic value of vested shares				$ 38,001	$ 98,829
Employee
Shares
Granted (in shares)			50,000
Employee | Vested at issuance
Shares
Vested (in shares)			(16,666)
Employee | Vested February 2017
Shares
Vested (in shares)		(16,667)
Employee | Vested February 2018
Shares
Vested (in shares)	(16,667)
Executive officers and directors
Shares
Granted (in shares)				247,694
Executive officers
Equity Incentive Plans
Vesting period				2 years
Directors
Equity Incentive Plans
Vesting period				1 year
Performance-based vesting | 2014 Equity Incentive Plan | Executive officers
Shares
Granted (in shares)				260,000

Income Taxes - Tax Cuts and Job

Income Taxes - Tax Cuts and Jobs Act (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Corporate tax rate (as a percent)		34.00%	34.00%	34.00%
Forecast
Corporate tax rate (as a percent)	21.00%

Income Taxes - Net operating lo

Income Taxes - Net operating loss carryforwards (Details) - Net Operating Losses $ in Millions	Dec. 31, 2017USD ($)
Federal
Net operating loss carryforwards
Net operating loss carryforwards	$ 202.1
State
Net operating loss carryforwards
Net operating loss carryforwards	$ 68.8

Income Taxes - Research and Dev

Income Taxes - Research and Development Tax Credit Carryforwards (Details) - Research and Development $ in Millions	Dec. 31, 2017USD ($)
Federal
Tax credit carryforwards
Tax credit carryforwards	$ 5.4
State
Tax credit carryforwards
Tax credit carryforwards	$ 0.9

Income Taxes -Deferred Taxes (D

Income Taxes -Deferred Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 47,427	$ 63,068
Research credit carryforward	6,296	5,284
Stock options and other	2,296	2,250
Total gross deferred tax assets	56,019	70,602
Valuation allowance for deferred tax assets	(56,019)	(70,602)
Net deferred tax assets	0	0
Income taxes
Deferred income tax expense or benefit	0	0
Valuation allowance
Increase (decrease) in net change in the valuation allowance	$ (14,600)	$ 10,400

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of U.S. Statutory Income Tax Rate to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate
Federal income tax at statutory rate (as a percent)	34.00%	34.00%	34.00%
State income tax benefit, net of federal benefit (as a percent)	6.00%	6.00%	6.00%
Research and development tax credits (as a percent)	3.00%	2.00%	2.00%
Effect of tax rate changes (as a percent)	(94.00%)	0.00%	0.00%
Other (as a percent)	(1.00%)	1.00%	(2.00%)
Decrease (increase) to valuation allowance (as a percent)	52.00%	(33.00%)	(24.00%)
Effective income tax rate (as a percent)	0.00%	10.00%	16.00%

Income Taxes - Sale of New Jers

Income Taxes - Sale of New Jersey Net Operating Losses (Details) - State - USD ($) $ in Millions	Nov. 30, 2015	Feb. 27, 2014	Dec. 31, 2016	Dec. 31, 2017
Net Operating Losses
Sale of New Jersey Net Operating Losses
NOLs				$ 68.8
Research and Development
Sale of New Jersey Net Operating Losses
Tax credits				$ 0.9
New Jersey | Sale of unused NOLs and research and development credits
Sale of New Jersey Net Operating Losses
Net proceeds from sale of NOL and tax credit	$ 6	$ 3.6	$ 3
New Jersey | Net Operating Losses | Sale of unused NOLs and research and development credits
Sale of New Jersey Net Operating Losses
NOLs	59.8	39.1	28.2
New Jersey | Research and Development | Sale of unused NOLs and research and development credits
Sale of New Jersey Net Operating Losses
Tax credits	$ 1.1	$ 0.4	$ 0.8

Related Party Transactions (Det

Related Party Transactions (Details) - SmartPharma $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jul. 06, 2016person
Related Party Transactions
Number of Managing Partners appointed to Chief Commercial Officer | person				1
Commercial and business development consulting services
Related Party Transactions
Fees invoiced by the related party | $	$ 0	$ 3	$ 73

Commitments and Contingencies59

Commitments and Contingencies (Details) $ in Thousands	Jan. 20, 2017complaint	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Operating Leases
Area of office space leased (in square feet) | ft²		8,200
Lease term		5 years
Rent expense		$ 193	$ 195	$ 163
Future minimum annual lease commitments under the non-cancelable operating lease
2,018		200
2,019		200
2,020		191
Total		$ 591
Legal Proceedings
Number of complaints filed in federal court | complaint	2

Subsequent Events - Sale of New

Subsequent Events - Sale of New Jersey Net Operating Losses (Details) - State - New Jersey - Sale of unused NOLs and research and development credits - USD ($) $ in Millions	Nov. 30, 2015	Feb. 27, 2014	Jan. 31, 2018	Dec. 31, 2016
Subsequent Events
Net proceeds in non-dilutive financing	$ 6	$ 3.6		$ 3
Subsequent Events
Subsequent Events
Net proceeds in non-dilutive financing			$ 0.5
Maximum lifetime benefit under the Program			$ 15
Subsequent Events | Minimum
Subsequent Events
Sale of unused Net Operating Loss Carryovers and unused Research and Development Tax Credits of the value of the tax benefits to unaffiliated (as a percent)			80.00%

Subsequent Events - Performance

Subsequent Events - Performance Based Restricted Stock Awards (Details) - Restricted stock units - shares	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Events
Granted (in shares)		247,694	50,000
2014 Equity Incentive Plan | Performance-based vesting | Executive officers
Subsequent Events
Granted (in shares)		260,000
2014 Equity Incentive Plan | Performance-based vesting | Subsequent Events | Executive officers
Subsequent Events
Granted (in shares)	365,000

Quarterly Data (Unaudited) - Qu

Quarterly Data (Unaudited) - Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Data (Unaudited)
Total revenue									$ 0
Operating expenses	$ 5,988	$ 6,701	$ 6,996	$ 7,126	$ 7,809	$ 7,091	$ 7,841	$ 6,980	26,811	$ 29,721	$ 33,089
Net loss	$ (6,240)	$ (7,102)	$ (7,446)	$ (7,516)	$ (5,201)	$ (7,804)	$ (8,418)	$ (7,318)	$ (28,304)	$ (28,741)	$ (30,335)
Basic and diluted net loss per common share (in dollars per share)	$ (0.18)	$ (0.22)	$ (0.26)	$ (0.26)	$ (0.18)	$ (0.27)	$ (0.29)	$ (0.27)	$ (0.91)	$ (1.02)	$ (1.38)

Quarterly Data (Unaudited) - Ta

Quarterly Data (Unaudited) - Tax Benefit from Sale of New Jersey State Net Operating Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
New Jersey | Sale of unused NOLs and research and development credits
Sale of New Jersey Net Operating Losses
Tax benefit	$ 0	$ 3.1