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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	EVOK
Entity Registrant Name	Evoke Pharma Inc
Entity Central Index Key	0001403708
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		15,493,368
Entity Public Float			$ 32.9

Balance Sheets - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 7,679,267	$ 9,007,071
Prepaid expenses	251,046	267,711
Other current assets		7,997
Total current assets	7,930,313	9,282,779
Other assets	11,551	11,551
Total assets	7,941,864	9,294,330
Current Liabilities:
Accounts payable and accrued expenses	1,048,927	478,223
Accrued compensation	1,025,911	933,450
Total current liabilities	2,074,838	1,411,673
Warrant liability	3,701,277	4,095,019
Total liabilities	5,776,115	5,506,692
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value; authorized shares — 5,000,000 at December 31, 2017 and 2016; issued and outstanding shares — 0 at December 31, 2017 and 2016
Common stock, $0.0001 par value; authorized shares — 50,000,000 at December 31, 2017 and 2016; issued and outstanding shares — 15,413,610 and 12,350,360 at December 31, 2017 and 2016, respectively	1,541	1,235
Additional paid-in capital	73,202,863	62,595,546
Accumulated deficit	(71,038,655)	(58,809,143)
Total stockholders' equity	2,165,749	3,787,638
Total liabilities and stockholders' equity	$ 7,941,864	$ 9,294,330

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	15,413,610	12,350,360
Common stock, shares outstanding	15,413,610	12,350,360

Statements of Operations - USD ($)	12 Months Ended
Statements of Operations - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 7,137,493	$ 6,951,600
General and administrative	4,093,189	3,592,825
Total operating expenses	11,230,682	10,544,425
Loss from operations	(11,230,682)	(10,544,425)
Other income (expense):
Interest income (expense), net	6,519	(268,029)
Financing costs related to warrant liability		(533,692)
Change in fair value of warrant liability	(1,005,349)	597,615
Total other expense, net	(998,830)	(204,106)
Net loss	$ (12,229,512)	$ (10,748,531)
Net loss per share of common stock, basic	$ (0.82)	$ (1.15)
Net loss per share of common stock, diluted	$ (0.90)	$ (1.15)
Weighted-average shares used to compute basic net loss per share	14,897,885	9,338,068
Weighted-average shares used to compute diluted net loss per share	14,951,036	9,338,068

Statements of Stockholders' Equity - USD ($)	Total	At-The-Market Offering [Member]	Common Stock [Member]	Common Stock [Member] At-The-Market Offering [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] At-The-Market Offering [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2015	$ 3,464,929		$ 720		$ 51,524,821		$ (48,060,612)
Beginning Balance, Shares at Dec. 31, 2015			7,201,774
Stock-based compensation expense	1,706,524				1,706,524
Issuance of common stock, net		$ 256,113		$ 6		$ 256,107
Issuance of common stock, shares net				56,000
Issuance of common stock from employee stock purchase plan	$ 98,742		$ 3		98,739
Issuance of common stock from employee stock purchase plan, Shares	34,067		34,067
Issuance of common stock from warrant exercise			$ 1		(1)
Issuance of common stock from warrant exercise, Shares			9,887
Issuance of common stock and warrants, net	$ 8,803,036		$ 505		8,802,531
Issuance of common stock and warrants, shares net			5,048,632
Reclassification of warrant liability due to warrant amendment and exercise	206,825				206,825
Net loss	(10,748,531)						(10,748,531)
Ending Balance at Dec. 31, 2016	$ 3,787,638		$ 1,235		62,595,546		(58,809,143)
Ending Balance, Shares at Dec. 31, 2016	12,350,360		12,350,360
Stock-based compensation expense	$ 1,819,431				1,819,431
Issuance of common stock, net	7,254,348		$ 278		7,254,070
Issuance of common stock, shares net			2,775,861
Issuance of common stock from employee stock purchase plan	$ 134,753		$ 7		134,746
Issuance of common stock from employee stock purchase plan, Shares	75,529		75,529
Issuance of common stock from warrant exercise			$ 21		(21)
Issuance of common stock from warrant exercise, Shares			211,860
Reclassification of warrant liability due to warrant amendment and exercise	$ 1,399,091				1,399,091
Net loss	(12,229,512)						(12,229,512)
Ending Balance at Dec. 31, 2017	$ 2,165,749		$ 1,541		$ 73,202,863		$ (71,038,655)
Ending Balance, Shares at Dec. 31, 2017	15,413,610		15,413,610

Statements of Cash Flows - USD ($)	12 Months Ended
Statements of Cash Flows - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (12,229,512)	$ (10,748,531)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	1,819,431	1,706,524
Non-cash interest		120,889
Financing costs allocated to warrant liability		533,692
Change in fair value of warrant liability	1,005,349	(597,615)
Change in operating assets and liabilities:
Prepaid expenses and other assets	24,662	554,014
Accounts payable and accrued expenses	663,165	(276,715)
Net cash used in operating activities	(8,716,905)	(8,707,742)
Financing activities
Payment on bank loan		(4,500,000)
Proceeds from issuance of common stock, net	7,389,101	354,855
Proceeds from issuance of common stock and warrants, net		13,168,803
Net cash provided by financing activities	7,389,101	9,023,658
Net increase (decrease) in cash and cash equivalents	(1,327,804)	315,916
Cash and cash equivalents at beginning of period	9,007,071	8,691,155
Cash and cash equivalents at end of period	7,679,267	9,007,071
Supplemental disclosure of cash flow information
Interest paid		169,813
Non-cash financing activities
Fair value of warrants issued to placement agent		$ 369,863
Reclassification of warrant liability to equity due to exercise of warrants	$ 1,399,091

Organization and Basis of Presentation	12 Months Ended
Organization and Basis of Presentation	Dec. 31, 2017
Organization And Basis Of Presentation [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Evoke Pharma, Inc. (the “Company”) was incorporated in the state of Delaware in January 2007. The Company is a publicly-held specialty pharmaceutical company focused primarily on the development of drugs to treat gastroenterological disorders and disease. Since its inception, the Company has devoted substantially all of its efforts to product development, raising capital and building infrastructure, and has not realized revenues from its planned principal operations. The Company does not anticipate realizing revenues for the foreseeable future. The Company’s activities are subject to the significant risks and uncertainties associated with any specialty pharmaceutical company that has substantial expenditures for research and development, including funding its operations. Clinical Trial Results In July 2016, the Company announced topline results from its Phase 3 clinical trial that evaluated the efficacy and safety of Gimoti™ (formerly known as EVK-001) in women with symptoms associated with diabetic gastroparesis. In this study, Gimoti did not achieve its primary endpoint of symptom improvement at Week 4. In December 2016, the Company had a pre-New Drug Application (“pre-NDA”) meeting with the U.S. Food and Drug Administration (“FDA”), in which FDA agreed that a comparative exposure pharmacokinetic (“PK”) trial was acceptable as a basis for submission of a Gimoti new drug application (“NDA”). The comparative exposure PK trial will serve as a portion of the full 505(b)(2) data package to include prior efficacy and safety data developed by the Company and FDA’s prior findings of safety and efficacy for the Listed Drug, Reglan Tablets. In March 2017, the Company met with FDA to discuss the design of the comparative exposure PK trial and certain other chemistry, manufacturing and controls related items associated with the proposed NDA submission. In October 2017, the Company announced positive topline results from the comparative exposure PK trial. The objective of the trial was to identify a dose of Gimoti that met the criteria for bioequivalence compared to the Reglan Tablets after nasal and oral administration to healthy volunteers under fasted conditions. Based on these results, the Company expects to submit the Gimoti NDA to FDA in the second quarter of 2018. Going Concern The Company has incurred recurring losses and negative cash flows from operations since inception and expects to continue to incur net losses for the foreseeable future until such time, if ever, that it can generate significant revenues from the sale of its sole product, Gimoti. The Company ended 2017 with approximately $7.7 million in cash and cash equivalents, and the Company anticipates that it will continue to incur losses from operations due to a planned NDA submission for Gimoti, pre-approval and pre-commercialization activities, including marketing and manufacturing of Gimoti, and general and administrative costs to support operations. As a result, the Company believes that there is substantial doubt about its ability to continue as a going concern for one year after the date these financial statements are issued. The determination as to whether the Company can continue as a going concern contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. In its report on the Company’s financial statements for the year ended December 31, 2017, the Company’s independent registered public accounting firm included an explanatory paragraph expressing substantial doubt regarding the Company’s ability to continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The Company’s net losses may fluctuate significantly from quarter to quarter and year to year. The Company believes that its current cash and cash equivalents will be sufficient to meet estimated working capital requirements and fund operations into October 2018. The Company will need to raise additional debt or equity financing to fund future operations. There can be no assurance that additional financing will be available when needed or on acceptable terms. If the Company is not able to secure adequate additional funding, the Company may be forced to make reductions in spending, extend payment terms with suppliers, and/or suspend or curtail planned programs. Any of these actions could materially harm the Company’s business, results of operations, financial condition and future prospects.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ materially from those estimates.

Segment Reporting

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment operating in the United States.

Cash and Cash Equivalents

The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents. Cash and cash equivalents include cash in readily available checking and savings accounts.

Fair Value of Financial Instruments

The carrying amounts of all financial instruments, including accounts payable and accrued expenses, and employee-related liabilities, are considered to be representative of their respective fair values because of the short-term nature of those instruments. Based on the borrowing rates currently available to the Company for loans with similar terms, the Company believes that the fair value of long-term debt approximates its carrying value.

Concentrations of Risk

Financial instruments that potentially subject the Company to significant credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in a federally insured financial institution in excess of federally insured limits. The Company has established guidelines designed to maintain safety and liquidity, has not experienced any losses in such accounts and believes the exposure to significant risk to the cash balance is minimal.

The Company relies on a contract research organization (“CRO”) to manage the preparation and submission of the planned NDA. If this CRO is unable to continue the management of the NDA preparation, the delays could adversely affect the timing of the Company’s NDA submission with FDA.

In addition, the Company relies on third-party manufacturers for the production of its drug candidate. If the third-party manufacturers are unable to continue manufacturing the Company’s drug candidate, or if the Company loses one of its sole source suppliers used in its manufacturing processes, the Company may not be able to meet any development needs or commercial supply demand for Gimoti, if approved by FDA, and the development and/or commercialization of Gimoti could be materially and adversely affected.

Warrant Accounting

Certain of the warrants to purchase shares of the Company’s common stock, issued as a part of the at-the-market registered direct offerings in July and August 2016, are classified as warrant liability and recorded at fair value. These warrants contain a feature that could require the transfer of cash in the event a change of control occurs without the authorization of our Board of Directors, and therefore, are classified as a liability in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 480.

The fair value of each warrant is estimated on the date of issuance, and each subsequent balance sheet date, using the Black-Scholes valuation model using the appropriate risk-free interest rate, expected term and volatility assumptions. The expected life of the warrant was calculated using the remaining life of the warrant. Due to our limited historical data as a public company, the estimated volatility is calculated based upon the Company’s historical volatility, supplemented, as necessary, with historical volatility of comparable companies in the biotechnology industry whose share prices are publicly available for a sufficient period of time. The risk-free rate is based upon U.S. Treasury securities with remaining terms similar to the expected term of the stock award being valued.

This warrant liability is subject to remeasurement at each balance sheet date and the Company recognizes any change in the fair value of the warrant liability in the statement of operations. The Company will continue to adjust the carrying value of the warrants for changes in the estimated fair value until the earlier of the modification, exercise or expiration of the warrants. At that time, the liabilities will be reclassified to additional paid-in capital, a component of stockholders’ equity. The Company anticipates that the value of the warrants could fluctuate from quarter to quarter and that such fluctuation could have a material impact on the Company’s financial statements.

Stock-Based Compensation

Stock-based compensation expense for stock option grants and employee stock purchases under the Company’s Employee Stock Purchase Plan (the “ESPP”) is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the employee’s requisite service period. The estimation of stock option and ESPP fair value requires management to make estimates and judgments about, among other things, employee exercise behavior, forfeiture rates and volatility of the Company’s common stock. The judgments directly affect the amount of compensation expense that will be recognized.

The Company grants stock options to purchase common stock to employees and members of the board of directors with exercise prices equal to the Company’s closing market price on the date the stock options are granted. The risk-free interest rate assumption was based on the yield of an applicable rate for U.S. Treasury instruments with maturities similar to those of the expected term of the award being valued. The weighted average expected term of options and employee stock purchases was calculated using the simplified method as prescribed by accounting guidance for stock-based compensation. This decision was based on the lack of relevant historical data due to the Company’s limited historical experience. In addition, due to the Company’s limited historical data, the estimated volatility was calculated based upon the Company’s historical volatility, supplemented, as necessary, with historical volatility of comparable companies in the biotechnology industry whose share prices are publicly available for a sufficient period of time. The assumed dividend yield was based on the Company never paying cash dividends and having no expectation of paying cash dividends in the foreseeable future.

Research and Development Expenses

Research and development costs are expensed as incurred and primarily include compensation and related benefits, stock-based compensation expense and costs paid to third-party contractors to perform research, conduct clinical trials and develop drug materials and delivery devices. The Company expenses costs relating to the purchase and production of pre-approval inventories as research and development expense in the period incurred until FDA approval is received.

The Company bases its expense accruals related to clinical studies on estimates of the services received and efforts expended pursuant to contracts with multiple research institutions and CROs that conduct and manage clinical studies on its behalf. The financial terms of these agreements vary from contract to contract and may result in uneven payment flows. Payments under some of these contracts depend on factors, such as the successful enrollment of patients, site initiation and the completion of clinical study milestones. Service providers typically invoice the Company monthly in arrears for services performed. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the Company does not identify costs that have begun to be incurred, or if the Company underestimates or overestimates the level of services performed or the costs of these services, actual expenses could differ materially from estimates. To date, the Company has not experienced significant changes in estimates of accrued research and development expenses after a reporting period. However, due to the nature of estimates, no assurance can be made that changes to the estimates will not be made in the future as the Company becomes aware of additional information about the status or conduct of clinical studies and other research activities.

The Company does not own or operate manufacturing facilities for the production of Gimoti, nor does it plan to develop its own manufacturing operations in the foreseeable future. The Company currently depends on third-party contract manufacturers for all of its required raw materials, drug substance and finished product for its preclinical research, product development and clinical trials. The Company has agreements with Cosma S.p.A. to supply metoclopramide for the manufacture of Gimoti, and with Thermo Fisher Scientific Inc., who recently acquired Patheon UK Limited, for product development and manufacturing of Gimoti. The Company currently utilizes a third-party consultant, which it engages on an as-needed, hourly basis, to manage product development and manufacturing contractors.

Income Taxes

The Company accounts for income taxes in accordance with ASC 740, Income Taxes. Under ASC 740, deferred tax assets and liabilities reflect the future tax consequences of the differences between the financial reporting and tax basis of assets and liabilities using current enacted tax rates. The Company provides a valuation allowance against net deferred tax assets unless, based upon the available evidence, it is more likely than not that the deferred tax assets will be realized.

The Company’s policy related to accounting for uncertainty in income taxes prescribes a recognition threshold and measurement attributed criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of common stock outstanding for the period, without consideration for common stock equivalents and adjusted for the weighted-average number of common shares outstanding that are subject to repurchase. The Company has excluded 45,000 shares of common stock subject to repurchase from the weighted-average number of common shares outstanding for the years ended December 31, 2017 and 2016. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of shares subject to repurchase, warrants for the purchase of common stock, options outstanding under the Company’s equity incentive plans and potential shares to be purchased under the ESPP. For the periods, 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:

	Year Ended December 31,
	2017	2016
Common stock subject to repurchase	45,000		45,000
Warrants to purchase common stock	2,744,500		3,323,876
Common stock options	2,131,624		1,275,624
Employee stock purchase plan	27,785		43,752
Total excluded securities	4,948,909		4,688,252

For the years ended December 31, 2017 and 2016, dilutive shares of 53,061 and 0, respectively, related to the outstanding warrants, were included in the diluted net loss per share of common stock calculation.

Recent Accounting Pronouncements

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 income statement. 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 lessees for capital and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. As discussed in Note 4, the Company’s only significant lease is its facility lease, which expires on December 31, 2018. Until the current lease is extended, or a new lease is entered into, the Company is uncertain as to the impact of its pending adoption of the new standard on the Company’s financial statements.

Debt	12 Months Ended
Debt	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt	3. Debt On August 4, 2016, the Company repaid in full the $4.5 million of outstanding principal and interest under the Loan and Security Agreement, dated as of May 28, 2014, as amended (the “Loan Agreement”), between the Company and Square 1 Bank, a division of Pacific Western Bank (“Square 1”). In connection with such repayment, the Loan Agreement was terminated, and all security, liens or other encumbrances on assets of the Company were released. The Company incurred $82,685 of loan origination costs related to this credit facility. The remaining unamortized costs of approximately $38,000 were charged to interest expense upon the payment of the loan in August 2016. In connection with the funding of the term loan, the Company issued to Square 1 a warrant to purchase 22,881 shares of the Company’s common stock at an exercise price of $5.90 per share, the closing price of the Company’s common stock on the day of funding of the credit facility. During July 2016, Square 1 converted its warrant by a “cashless” conversion and received 9,887 shares of the Company’s common stock. The value determined for the warrant at the time of the grant of $108,122 was recorded as a debt discount, as well as to stockholders’ equity. The remaining unamortized debt discount associated with the warrant of approximately $59,000 was charged to interest expense upon the payment of the loan in August 2016. Total interest incurred under the loan and security agreements for the years ended December 31, 2017 and 2016 was $0 and $148,500, respectively.

Commitments	12 Months Ended
Commitments	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments	4. Commitments In December 2016, the Company entered into an operating lease for office space in Solana Beach, California. The lease commenced on January 1, 2017 with an expiration date of December 31, 2018. The Company has an option to extend the lease for an additional two years subject to specified prior written notice. The lease contains annual rent increases. Rent expense for 2017 and 2016 was approximately $135,000 and $116,000, respectively. The Company also pays pass through costs and utility costs, which are expensed as incurred. As of December 31, 2017, the Company has future minimum lease payments under its facility lease in 2018 of approximately $139,000.

Technology Acquisition Agreement

12 Months Ended

Dec. 31, 2017

Technology Acquisition Agreement [Abstract]

Technology Acquisition Agreement

5. Technology Acquisition Agreement

In June 2007, the Company acquired all worldwide rights, data, patents and other related assets associated with Gimoti from Questcor Pharmaceuticals, Inc. (“Questcor”) pursuant to an Asset Purchase Agreement. The Company paid Questcor $650,000 in the form of an upfront payment and $500,000 in May 2014 as a milestone payment based upon the initiation of the first patient dosing in the Company’s Phase 3 clinical trial for Gimoti. In August 2014, Mallinckrodt, plc, (“Mallinckrodt”) acquired Questcor. As a result of that acquisition, Questcor transferred its rights included in the Asset Purchase Agreement with the Company to Mallinckrodt. In addition to the payments made to Questcor, the Company may also be required to make additional milestone payments to Mallinckrodt totaling up to $51.5 million. These milestones include up to $4.5 million in payments if Gimoti achieves the following development targets:

•

$1.5 million upon FDA acceptance for review of an NDA for Gimoti; and

•

$3 million upon FDA approval of Gimoti.

The remaining $47 million in milestone payments depend on Gimoti’s commercial success and will only apply if Gimoti receives regulatory approval. In addition, the Company will be required to pay to Mallinckrodt a low single digit royalty on net sales of Gimoti. The Company’s obligation to pay such royalties will terminate upon the expiration of the last patent right covering Gimoti, which is expected to occur in 2030.

Preferred Stock, Common Stock and Stockholders' Equity

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Preferred Stock, Common Stock and Stockholders' Equity

6. Preferred Stock, Common Stock and Stockholders’ Equity

Preferred Stock

Under the Company’s amended and restated certificate of incorporation, the Company is authorized to issue 5,000,000 shares of preferred stock with a $0.0001 par value. No shares of preferred stock were outstanding as of December 31, 2017 or 2016.

Common Stock

As of December 31, 2017, there were 15,413,610 shares of common stock outstanding. Each share of common stock is entitled to one vote. The holders of the common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors of the Company. To date, no dividends have been declared.

Sale of Common Stock and Warrants

On July 25, 2016, the Company completed a registered direct offering of 1,804,512 shares of common stock at a purchase price of $2.49375 per share (the “July 2016 Financing”). Concurrently in a private placement, for each share of common stock purchased by an investor, such investor received from the Company an unregistered warrant to purchase three-quarters of a share of common stock, for a total of 1,353,384 shares (the “July Warrants”). The July Warrants have an exercise price of $2.41 per share, are immediately exercisable and will expire on January 25, 2022. The aggregate gross proceeds from the sale of the common stock and warrants were $4.5 million, and the net proceeds after deduction of commissions and fees were $4.0 million.

In connection with the July 2016 Financing, the Company issued to its placement agent, Rodman & Renshaw, a unit of H.C. Wainwright & Co. LLC (“Wainwright”), and its designees unregistered warrants to purchase an aggregate of 90,226 shares of the Company’s common stock (the “July Wainwright Warrants”). The July Wainwright Warrants have substantially the same terms as the July Warrants, except that the July Wainwright Warrants will expire on July 21, 2021 and have an exercise price equal to $3.1172 per share of common stock.

On August 3, 2016, the Company completed a registered direct offering of 3,244,120 shares of common stock at a purchase price of $3.0825 per share (the “August 2016 Financing”) and together with the July 2016 Financing (the “2016 Financings”). Concurrently in a private placement, for each share of common stock purchased by an investor, such investor received from the Company an unregistered warrant to purchase one half of a share of common stock, for a total of 1,622,060 shares (the “August Warrants”). The August Warrants have an exercise price of $3.03 per share, are immediately exercisable and will expire on February 3, 2022. The aggregate gross proceeds from the sale of the common stock and warrants were $10 million, and the net proceeds after deduction of commissions and fees was approximately $9.2 million.

In connection with the August 2016 financing, the Company issued to its placement agent, Wainwright, and its designees unregistered warrants to purchase an aggregate of 162,206 shares of the Company’s common stock (the “August Wainwright Warrants”). The August Wainwright Warrants have substantially the same terms as the August Warrants, except that the August Wainwright Warrants will expire on July 29, 2021 and have an exercise price equal to $3.853125 per share of common stock.

The warrants issued in connection with the 2016 Financings had a total initial fair value of $4,899,459 on their respective closing dates as determined using the Black Scholes valuation model and such value was recorded as the initial carrying value of the warrant liability. The fair value of the warrants is remeasured at each financial reporting period with any change in fair value recognized as a change in fair value of the warrant liability in the Statement of Operations.

On December 15, 2016, the Company entered into amendments (the “Warrant Amendments”) with certain of the holders (the “Holders”) of the Company’s outstanding warrants to purchase common stock issued on July 25, 2016 and August 3, 2016. Pursuant to the Warrant Amendments, the Holders’ right to require the Company to purchase the outstanding warrants upon the occurrence of certain fundamental transactions will not apply if the fundamental transaction is a result of a transaction that has not been approved by the Company’s board of directors. As a result of this amendment, warrants to purchase 252,432 shares of the Company’s common stock were no longer required to be classified as liabilities. The value of amended warrants were adjusted to their fair value immediately prior to the amendment and approximately $207,000 was reclassified from warrant liability to Additional Paid-in Capital.

On February 16, 2017, an institutional investor from the Company’s financing which closed in July 2016 converted its warrant to purchase 526,315 shares of our common stock by a “cashless” exercise and received 211,860 shares of the Company’s common stock. The warrant had an exercise price of $2.41 per share. The shares were issued, and the warrants were sold, in reliance upon the registration exemption set forth in Section 4(a)(2) of the Securities Act of 1933, as amended. The value of the exercised warrants were adjusted to their fair value immediately prior to the exercise and approximately $1.4 million was reclassified from warrant liability to Additional Paid-in Capital. Subsequent to this transaction, warrants to purchase 2,449,129 shares of the Company’s common stock remain classified as a liability.

Sale of Common Stock in Public Offering

In February and March 2017, the Company completed the sale of 2,775,861 shares of its common stock in an underwritten public offering led by Laidlaw & Company (UK) Ltd. The price to the public in this offering was $2.90 per share resulting in gross proceeds to the Company of approximately $8.0 million. After deducting underwriting discounts and commissions and offering expenses paid by the Company, the net proceeds to the Company from this offering was approximately $7.3 million.

At the Market Equity Offering Program

On April 15, 2016, the Company terminated its At Market Sales Agreement with MLV & Co. LLC and entered into a new At Market Issuance Sales Agreement with B. Riley FBR, Inc. (as successor by merger to FBR Capital Markets & Co., “FBR”) (“FBR Sales Agreement”), and filed a prospectus supplement, pursuant to which the Company may sell from time to time, at its option, up to an aggregate of 649,074 shares of the Company’s common stock through FBR as the sales agent. The sales of shares made through this equity program are made in “at-the-market” offerings as defined in Rule 415 of the Securities Act. Through December 31, 2016, the Company sold 56,000 shares of common stock at a weighted average price per share of $5.45 and received proceeds of approximately $296,000, net of commissions and fees.

In November 2017, the Company filed a new shelf registration with the SEC on Form S-3 to replace a prior Form S-3 shelf registration which was set to expire on November 25, 2017. This new shelf registration was declared effective by the SEC on December 28, 2017. The new shelf registration statement includes a prospectus for the at-the-market offering to sell up to an aggregate of $16.0 million of shares of the Company’s common stock through FBR as a sales agent. The Company did not sell any shares of common stock through the FBR Sales Agreement during 2017. Through February 28, 2018, the Company sold 79,758 shares of common stock at a weighted average price per share of $2.08 pursuant to the FBR Sales Agreement and received net proceeds of approximately $160,000, net of commissions and fees. The Company currently has the capacity to issue up to approximately $11.9 million worth of additional shares of common stock pursuant to the FBR Sales Agreement.

Under current SEC regulations, if at the time the Company files its Annual Report on Form 10-K, or Form 10-K, the Company’s public float is less than $75 million, and for so long as its public float remains less than $75 million, the amount the Company can raise through primary public offerings of securities in any twelve-month period using shelf registration statements is limited to an aggregate of one-third of the Company’s public float, which is referred to as the baby shelf rules. As of February 28, 2018, the Company’s public float was approximately $36.1 million, based on 12,938,176 shares of outstanding common stock held by non-affiliates and at a price of $2.79 per share, which was the last reported sale price of the Company’s common stock on The Nasdaq Capital Market on January 29, 2018. As a result of the Company’s public float being below $75 million, the Company will be limited by the baby shelf rules until such time as the Company’s public float exceeds $75 million, which means the Company only has the capacity to sell shares up to one-third of its public float under shelf registration statements in any twelve-month period. If the Company’s public float decreases, the amount of securities we may sell under our Form S-3 shelf registration statement will also decrease.

Future sales will depend on a variety of factors including, but not limited to, market conditions, the trading price of the Company’s common stock and the Company’s capital needs. There can be no assurance that FBR will be successful in consummating future sales based on prevailing market conditions or in the quantities or at the prices that the Company deems appropriate.

In addition, the Company will not be able to make future sales of common stock pursuant to the FBR Sales Agreement unless certain conditions are met, which include the accuracy of representations and warranties made to FBR under the FBR Sales Agreement. Furthermore, FBR is permitted to terminate the FBR Sales Agreement in its sole discretion upon ten days’ notice, or at any time in certain circumstances, including the occurrence of an event that would be reasonably likely to have a material adverse effect on the Company’s assets, business, operations, earnings, properties, condition (financial or otherwise), prospects, stockholders’ equity or results of operations. The Company has no obligation to sell the remaining shares available for sale pursuant to the FBR Sales Agreement.

Warrants

The Company has issued warrants to purchase common stock to banks that have loaned funds to the Company, as well as to representatives of the underwriters of the Company’s initial public offering and certain of its affiliates. A summary of the Company’s warrant activity is as follows:

						Weighted
				Weighted		Average
				Average		Remaining
				Exercise		Contractual
	Shares			Price		Term (Years)
Outstanding at December 31, 2016		3,323,876		$	3.29		4.96
Issued	—			—			—
Exercised		(526,315	)	$	2.41		4.07
Expired/Forfeited	—			—			—
Outstanding at December 31, 2017		2,797,561		$	3.46		3.94

Equity Incentive Award Plans

The Company adopted the 2007 Equity Incentive Plan (the “2007 Plan”) in May 2007 under which 450,000 shares of common stock were reserved for issuance to employees, nonemployee directors and consultants of the Company. As of December 31, 2016, no options were available for future grant under this plan.

In August 2013, the Company adopted the 2013 Equity Incentive Award Plan (the “2013 Plan”) as a successor to the 2007 Plan. Under the 2013 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then employees, officers, non-employee directors or consultants of the Company. A total of 510,000 shares of common stock were initially reserved for issuance under the 2013 Plan. In addition, the number of shares of common stock available for issuance under the 2013 Plan will be annually increased on the first day of each fiscal year during the term of the 2013 Plan, beginning with the 2014 fiscal year, by an amount equal to the least of: (i) 300,000 shares; (ii) four percent of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year; or (iii) such other amount as the Company’s board of directors may determine.

In February 2016, the Company effected a one-time option exchange, wherein employees were offered the opportunity to exchange certain outstanding stock options for the grant of a lesser number of replacement stock options. The participants received three new stock options for every four stock options tendered for exchange. As a result, 703,500 stock options were exchanged for 527,624 replacement stock options. The replacement stock options have a three-year vesting schedule and an exercise price of $3.04 per share, which was the closing price of the Company’s common stock on the date of the option exchange. All other terms of the replacement stock options remain the same as the original stock options that were exchanged. As a result of this transaction, the Company recognized an incremental stock-based compensation expense of approximately $4,700 at the time of the transaction and will recognize an additional approximately $141,000 of stock-based compensation expense over the three-year vesting term of the exchanged options.

On April 27, 2016, the Company’s stockholders approved an amendment and restatement of the Company’s 2013 Equity Incentive Award Plan (the “Restated Plan”) to increase the number of shares of common stock reserved under the Restated Plan by 500,000 shares, to an aggregate of 4,786,425 shares, and to extend the term of the Restated Plan into 2026.

As a result of the annual increases since the 2013 Plan originated, and the increase of stock options reserved under the Restated Plan approved by the Company’s stockholders in April 2016, the Company has increased the number shares reserved for issuance under the 2013 Plan by 1,276,425 shares. As of December 31, 2017, 72,801 options remain available for future grant under the 2013 Plan. On January 1, 2018, the Company further increased the number of shares reserved for issuance under the 2013 Plan by 300,000 shares, making 372,801 options available for future grant under the 2013 Plan.

Options granted under the 2007 Plan and 2013 Plan have ten year terms from the date of grant and generally vest over a one to four year period. The Company granted options to purchase 856,000 and 414,000 shares of common stock in 2017 and 2016, respectively. The exercise price of all options granted during the years ended December 31, 2017 and 2016 was equal to the market value per share of the Company’s common stock on the date of grant.

A summary of the Company’s stock option activity under the 2007 Plan and 2013 Plan is as follows:

					Weighted
			Weighted		Average
			Average		Remaining
			Exercise		Contractual		Aggregate
	Shares		Price		Term (Years)		Intrinsic Value
Outstanding at December 31, 2016		1,275,624	$	4.04		8.34	$	191,160
Granted		856,000	$	2.45		9.13	—
Exercised	—		—		—		—
Expired/Forfeited/Exchanged	—		—		—		—
Outstanding at December 31, 2017		2,131,624	$	3.40		8.06	$	219,480
Vested and expected to vest at December 31, 2017		2,131,624	$	3.40		8.06	$	219,480
Exercisable at December 31, 2017		1,111,270	$	4.08		7.38	$	219,480

The intrinsic values above represent the aggregate value of the total pre-tax intrinsic value based upon a common stock price of $2.26 and $2.02 at December 31, 2017 and 2016, respectively, and the contractual exercise price.

The weighted average grant date fair value per share of employee stock options granted during the years ended December 31, 2017 and 2016, was $1.87 and $2.04, respectively.

The 2007 Plan permits the early exercise of options, but the Company has the option to repurchase any unvested shares at the original purchase price (the exercise price paid by the purchaser) upon any voluntary or involuntary termination. The shares of common stock issued from the exercise of stock options are restricted and vest over time or on the achievement of certain milestones. Any unvested shares immediately vest in the event of termination for reasons other than cause, and vesting accelerates in the event of a merger, sale, or other change in control of the Company. Of the total 332,000 stock options exercised, 287,000 were vested as of December 31, 2017 and 2016. The remaining 45,000 exercised stock options vest upon the submission of the NDA for Gimoti.

There were no options exercised in 2017 and 2016.

The Company had the following nonvested options under the 2007 Plan and 2013 Plan:

	Shares			Weighted Average Grant Date Fair Value Per Share
Nonvested at December 31, 2016		690,961		$	3.34
Granted		856,000		$	2.45
Vested		(526,607	)	$	3.22
Expired/Forfeited/Exchanged		—			—
Nonvested at December 31, 2017		1,020,354		$	2.65

Employee Stock Purchase Plan

On June 13, 2013, the Company’s board of directors adopted the ESPP, and the Company’s stockholders approved the ESPP on August 29, 2013. The ESPP became effective on the day prior to the effectiveness of the IPO. The ESPP permits participants to purchase the Company’s common stock at 85% of the fair market value through payroll deductions of up to 20% of their eligible compensation. A total of 30,000 shares of common stock were initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP has been annually increased on the first day of each fiscal year during the term of the ESPP by an amount equal to the lesser of: (i) 30,000 shares; (ii) one percent of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year; or (iii) such other amount as the Company’s board of directors may determine.

On May 3, 2017, the Company’s stockholders approved an amendment and restatement of the Company’s ESPP to increase the number of shares of common stock reserved under the ESPP by 100,000 shares (to an aggregate of 1,250,000 shares), to increase the annual evergreen provision from 30,000 shares to 100,000 shares, and to extend the term of the ESPP into 2027. As a result, the Company increased the number shares reserved for issuance under the ESPP by 220,000 shares since the inception of the ESPP. As of December 31, 2017, 91,934 shares remain available for future issuance under the ESPP. On January 1, 2018, the Company further increased the number of shares reserved for future issuance under the ESPP by 100,000 shares, making 191,934 shares available for future issuance under the ESPP after that increase.

Payroll withholdings from the Company’s employees of approximately $135,000 and $99,000 resulted in the issuance of 75,529 and 34,067 shares of common stock through its ESPP during the years ended December 31, 2017 and 2016, respectively.

The estimated fair value of the shares to be acquired under the ESPP was determined on the initiation date of each six month purchase period using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for ESPP shares to be purchased during the year ended December 31, 2017 and 2016:

	Year Ended December 31,
	2017	2016
Risk free interest rate	0.79% - 1.10%	0.47% - 0.50%
Expected term	6 months	6 months
Expected volatility of common stock	37.60% - 99.23%	83.83% - 212.80%
Expected dividend yield	0.0%		0.0%

Stock-Based Compensation

Stock-based compensation expense includes charges related to stock option grants and employee stock purchases under the Company’s ESPP. The Company measures stock-based compensation expense based on the grant-date fair value of any awards granted to its employees. Such expense is recognized over the period of time that employees provide service and earn rights to the awards.

The estimated fair value of each option award granted was determined on the date of grant using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for options grants during the two years ended December 31, 2017:

	Year Ended December 31,
	2017	2016
Risk free interest rate	1.93% - 2.16%	1.25% - 1.58%
Expected option term	5.5 - 6.0 years	5.3 - 6.0 years
Expected volatility of common stock	94.05% - 98.23%	74.44 - 75.91%
Expected dividend yield	0.0%		0.0%

The Company recognized non-cash stock-based compensation expense to employees and directors in its research and development and its general and administrative functions as follows:

	Year Ended December 31,
	2017		2016
Research and development	$	819,815	$	698,032
General and administrative		999,616		1,008,492
Total stock-based compensation expense	$	1,819,431	$	1,706,524

As of December 31, 2017, there was approximately $1.7 million of unrecognized compensation costs related to outstanding employee and board of director options, which is expected to be recognized over a weighted average period of 1.13 years.

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following at December 31, 2017 and 2016:

	December 31,
	2017		2016
Stock options issued and outstanding		2,131,624		1,275,624
Authorized for future option grants		72,801		628,801
Warrants to purchase common stock		2,797,561		3,323,876
Authorized for employee stock purchase plan		91,934		37,463
Total common stock reserved for future issuance		5,093,920		5,265,764

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

7. Fair Value Measurements

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date.

As noted in Note 6, during the third quarter of 2016 the Company entered into the 2016 Financings with an institutional investor providing for the issuance and sale by the Company of 5,048,632 shares of the Company’s common stock and warrants to purchase up to 2,975,444 shares of the Company’s common stock for aggregate gross proceeds of $14.5 million. In addition, as partial payment for services, the Company issued to the underwriters warrants to purchase up to 252,432 shares of the Company’s common stock.

The Company utilizes a valuation hierarchy for disclosure of the inputs to the valuations used to measure fair value. This hierarchy prioritizes the inputs into three broad levels as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument. Level 3 inputs are unobservable inputs based on the Company’s own assumptions used to measure assets and liabilities at fair value. A financial asset or liability’s classification within the hierarchy is determined based on the lowest level input that is significant to the fair value measurement.

The Company had no assets or liabilities classified as Level 1 or Level 2. The warrant liability is classified as Level 3.

The Company has classified the warrants as a liability and has remeasured the liability to estimated fair value at December 31, 2017 and 2016, using the Black Scholes option valuation model with the following assumptions:

	December 3l,
	2017	2016
Risk-free interest rate	2.09%	1.93%
Expected volatility	100.39%	94.19%
Expected term	4.08 years	5.08 years
Expected dividend yield	0.0%	0.0%

The following fair value hierarchy table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017:

	Fair Value Measurement as of December 31, 2017
	Level 1		Level 2		Level 3		Balance
Warrant liability	$	-	$	-	$	3,701,277	$	3,701,277
Total	$	-	$	-	$	3,701,277	$	3,701,277

The following table presents a reconciliation of the Company’s warrant liability measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the years ended December 31, 2017 and 2016:

	December 31,
	2017			2016
Beginning balance of warrant liability	$	4,095,019		$	-
Issuance of warrants		-			4,899,459
Change in fair value upon re-measurement		1,005,349			(597,615	)
Reclassification to Additional Paid-in Capital due to warrant amendment		-			(206,825	)
Reclassification to Additional Paid-in Capital due to warrant exercise		(1,399,091	)		-
Ending balance of warrant liability	$	3,701,277		$	4,095,019

There were no transfers between Level 1 and Level 2 in any of the periods reported.

- Definition

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

+ References + Details

Employee Benefit Plan	12 Months Ended
Employee Benefit Plan	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plan	8. Employee Benefit Plan The Company has established a defined contribution 401(k) plan (the “Plan”) for all employees who are at least 21 years of age. Employees are eligible to participate in the Plan beginning on the date of employment. Under the terms of the Plan, employees may make voluntary contributions as a percentage of compensation. The Company’s contributions to the Plan are discretionary, and no contributions have been made by the Company to date. For the years ended December 31, 2017 and 2016, the Company adopted Safe Harbor 401(k) provisions. In order to maintain the Plan’s compliance with Internal Revenue Service regulations, approximately $3,700 was contributed to the accounts of certain employees for the year ended December 31, 2016 and approximately $3,500 will be contributed to the accounts of certain employees for the year ended December 31, 2017.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

9. Income Taxes

The Company accounts for uncertain tax positions in accordance with Accounting Standards Codification Topic 740, Income Taxes (“ASC 740”). The application of income tax law and regulations is inherently complex. Interpretations and guidance surrounding income tax laws and regulations change over time. As such, changes in the Company’s subjective assumptions and judgments can materially affect amounts recognized in its financial statements.

The Company’s policy is to recognize interest and/or penalties related to income tax matters in income tax expense. The Company had no accrual for interest and penalties on the balance sheet at December 31, 2017. The Company has an uncertain tax position of $1.9 million related to California net operating losses at December 31, 2017. The Company is subject to taxation in the United States and state jurisdictions, and the Company’s tax years beginning 2007 to date are subject to examination by taxing authorities.

On December 22, 2017, President Trump signed into law the tax legislation commonly known as the Tax Cuts and Jobs Act (the “Act”). The effects of the new federal legislation are recognized upon enactment, which is the date the president signs a bill into law. The Act includes numerous changes in existing tax law, including a permanent reduction in the federal corporate income tax rate from 35% to 21%. The rate reduction takes effect on January 1, 2018. As a result of this rate change, the Company has revalued its deferred tax assets at December 31, 2017. Deferred income taxes result from temporary differences between the tax basis of assets and liabilities and their reported amounts in the financial statements that will result in taxable or deductible amounts in future years. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to faxable income in years in which those temporary differences are expected to be recovered or settled. As changes in tax laws or rates are enacted, deferred tax assets and liabilities are adjusted through income tax expense. Based on currently available information, the Company recorded a reduction of approximately $7.9 million in the fourth quarter of 2017 related to the revaluation of its deferred tax assets, which did not result in additional tax expense in the quarter as the Company’s deferred tax assets have a full valuation allowance. This amount may be subject to further adjustment in subsequent periods throughout 2018 in accordance with subsequent interpretive guidance issued by the SEC or the IRS. Further, there may be other material adverse effects resulting from the legislation that we have not yet identified.

A reconciliation of the federal statutory income tax rate and the effective income tax rate is as follows for the years ended December 31, 2017 and 2016:

	December 31,
	2017			2016
	(%)			(%)
Federal statutory rate		34			34
Warrant liability FMV adjustment		(8	)		6
Stock issuance costs	—				(5	)
Research and development credits		3			3
Removal of net operating loss and other credits		33			(33	)
Impact of federal tax rate change		(65	)	—
Stock compensation and other permanent items		3			(5	)
Effective income tax rate	—			—

Pursuant to Internal Revenue Code (“IRC”) Sections 382 and 383, annual use of the Company’s net operating loss and research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period. The Company has not completed an IRC Section 382/383 analysis regarding the limitation of net operating loss and research and development credit carryforwards. Until this analysis has been completed, the Company has removed the deferred tax assets for net operating losses of approximately $15.9 million and a research and development credit of approximately $3.0 million generated through December 31, 2017 from its deferred tax asset schedule, and has recorded a corresponding decrease to its valuation allowance. When this analysis is finalized, the Company plans to update its unrecognized tax benefits accordingly. The Company does not expect this analysis to be completed within the next twelve months and, as a result, the Company does not expect that the unrecognized tax benefits will change within twelve months of this reporting date. Due to the existence of the valuation allowance, future changes in the Company’s unrecognized tax benefits will not impact the Company’s effective tax rate.

Significant components of the Company’s deferred tax assets at December 31, 2017 and 2016 are as follows:

	December 31,
	2017			2016
Acquired technology	$	103,000		$	201,000
Stock compensation expense		490,000			539,000
Accruals and other		216,000			130,000
Total deferred tax assets		809,000			870,000
Less valuation allowance		(809,000	)		(870,000	)
Net deferred tax assets	$	—		$	—

At December 31, 2017, the Company has federal and California net operating loss carryforwards of approximately $61.9 million and $41.7 million, respectively. The federal and California loss carryforwards begin to expire in 2027 and 2017, respectively, unless previously utilized. The Company also has federal and California research tax credit carryforwards of approximately $2.0 million and $1.2 million, respectively. The federal research credit carryforwards will begin expiring in 2027 unless previously utilized. The California research credit will carry forward indefinitely. Furthermore, under recently enacted U.S. tax legislation, although the treatment of tax losses generated before December 31, 2017 has generally not changed, tax losses generated in calendar year 2018 and beyond may only offset 80% of our taxable income. This change may require us to pay federal income taxes in future years despite generating a loss for federal income tax purposes in prior years.

A summary of the changes in the amount of unrecognized tax benefits (excluding interest and penalties) for 2017 and 2016 are as follows:

	2017		2016
Beginning balance of unrecognized tax benefits	$	1,961,595	—
Additions based on tax positions of prior years	—		$	1,961,595
Ending balance of unrecognized tax benefits	$	1,961,595	$	1,961,595

Due to the full valuation allowance that the Company has on the deferred tax assets, there are no unrecognized tax benefits that would impact the effective tax rate, if recognized.

The Company recognizes interest and penalties related to unrecognized tax benefits in income tax expense. To date, as no benefit has been taken related to the uncertain tax position, there have been no interest and penalties recognized.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	10. Subsequent Events For the purposes of the financial statements as of December 31, 2017 and the year then ended, the Company has evaluated subsequent events through the date the audited annual financial statements were issued. The Company has concluded that no subsequent event has occurred other than what has been disclosed.

Summarized Quarterly Data (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Summarized Quarterly Data (Unaudited)

11. Summarized Quarterly Data (Unaudited)

The following financial information reflects all adjustments, which include only normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the financial results of the interim periods. Summarized quarterly data for the years ended December 31, 2017 and 2016 are as follows:

	For the Quarters Ended
	March 31,			June 30,				September 30,			December 31,
2017
Research and development expense	$	770,686		$	2,017,569			$	2,717,698		$	1,631,540
General and administrative expense	$	1,209,570		$	871,979			$	984,047		$	1,027,594
Change in fair value of warrant liability	$	3,072,747		$	(1,261,912	)		$	1,544,138		$	(2,349,624	)
Net loss	$	(5,052,039	)	$	(1,625,969	)		$	(5,243,061	)	$	(308,443	)
Net loss per common share, basic⁽¹⁾	$	(0.37	)	$	(0.11	)		$	(0.34	)	$	(0.02	)
Net loss per common share, diluted⁽¹⁾	$	(0.37	)	$	(0.13	)	⁽²⁾	$	(0.34	)	$	(0.07	)
Weighted average shares outstanding, basic		13,528,311			15,343,325				15,351,295			15,368,610
Weighted average shares outstanding, diluted		13,528,311			15,420,954				15,351,295			15,503,583

2016
Research and development expense	$	2,015,076		$	2,095,149			$	1,339,343		$	1,502,032
General and administrative expense	$	1,137,753		$	802,655			$	830,092		$	822,325
Change in fair value of warrant liability	—			—				$	198,945		$	(796,560	)
Net loss	$	(3,225,409	)	$	(2,970,498	)		$	(3,025,281	)	$	(1,527,343	)
Net loss per common share, basic and diluted⁽¹⁾	$	(0.45	)	$	(0.41	)		$	(0.29	)	$	(0.12	)
Weighted average shares outstanding, basic and diluted		7,168,005			7,217,577				10,614,692			12,305,360

(1)	Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation.

(2)	Net loss per common share, diluted, for the quarter ended June 30, 2017 was revised from ($0.19) to ($0.13) to correct the computation of diluted loss per share under the treasury stock method. No adjustments were made to any other quarters.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Use of Estimates

Segment Reporting

Cash and Cash Equivalents

Fair Value of Financial Instruments

Concentrations of Risk

Warrant Accounting

Stock-Based Compensation

Research and Development Expenses

Income Taxes

Net Loss Per Share

	Year Ended December 31,
	2017	2016
Common stock subject to repurchase	45,000		45,000
Warrants to purchase common stock	2,744,500		3,323,876
Common stock options	2,131,624		1,275,624
Employee stock purchase plan	27,785		43,752
Total excluded securities	4,948,909		4,688,252

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Outstanding Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share

For the periods, 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:

	Year Ended December 31,
	2017	2016
Common stock subject to repurchase	45,000		45,000
Warrants to purchase common stock	2,744,500		3,323,876
Common stock options	2,131,624		1,275,624
Employee stock purchase plan	27,785		43,752
Total excluded securities	4,948,909		4,688,252

Preferred Stock, Common Stock and Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Summary of Warrants Activity

A summary of the Company’s warrant activity is as follows:

						Weighted
				Weighted		Average
				Average		Remaining
				Exercise		Contractual
	Shares			Price		Term (Years)
Outstanding at December 31, 2016		3,323,876		$	3.29		4.96
Issued	—			—			—
Exercised		(526,315	)	$	2.41		4.07
Expired/Forfeited	—			—			—
Outstanding at December 31, 2017		2,797,561		$	3.46		3.94

Summary of Stock Option Activity

A summary of the Company’s stock option activity under the 2007 Plan and 2013 Plan is as follows:

					Weighted
			Weighted		Average
			Average		Remaining
			Exercise		Contractual		Aggregate
	Shares		Price		Term (Years)		Intrinsic Value
Outstanding at December 31, 2016		1,275,624	$	4.04		8.34	$	191,160
Granted		856,000	$	2.45		9.13	—
Exercised	—		—		—		—
Expired/Forfeited/Exchanged	—		—		—		—
Outstanding at December 31, 2017		2,131,624	$	3.40		8.06	$	219,480
Vested and expected to vest at December 31, 2017		2,131,624	$	3.40		8.06	$	219,480
Exercisable at December 31, 2017		1,111,270	$	4.08		7.38	$	219,480

Summary of Nonvested Options Activity

The Company had the following nonvested options under the 2007 Plan and 2013 Plan:

	Shares			Weighted Average Grant Date Fair Value Per Share
Nonvested at December 31, 2016		690,961		$	3.34
Granted		856,000		$	2.45
Vested		(526,607	)	$	3.22
Expired/Forfeited/Exchanged		—			—
Nonvested at December 31, 2017		1,020,354		$	2.65

Summary of Estimated Fair Value of Employee Stock Purchase Plan Award

	Year Ended December 31,
	2017	2016
Risk free interest rate	0.79% - 1.10%	0.47% - 0.50%
Expected term	6 months	6 months
Expected volatility of common stock	37.60% - 99.23%	83.83% - 212.80%
Expected dividend yield	0.0%		0.0%

Summary of Estimated Fair Value of Stock Option Award

	Year Ended December 31,
	2017	2016
Risk free interest rate	1.93% - 2.16%	1.25% - 1.58%
Expected option term	5.5 - 6.0 years	5.3 - 6.0 years
Expected volatility of common stock	94.05% - 98.23%	74.44 - 75.91%
Expected dividend yield	0.0%		0.0%

Summary of Recognized Non-Cash Stock-Based Compensation Expense

The Company recognized non-cash stock-based compensation expense to employees and directors in its research and development and its general and administrative functions as follows:

	Year Ended December 31,
	2017		2016
Research and development	$	819,815	$	698,032
General and administrative		999,616		1,008,492
Total stock-based compensation expense	$	1,819,431	$	1,706,524

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following at December 31, 2017 and 2016:

	December 31,
	2017		2016
Stock options issued and outstanding		2,131,624		1,275,624
Authorized for future option grants		72,801		628,801
Warrants to purchase common stock		2,797,561		3,323,876
Authorized for employee stock purchase plan		91,934		37,463
Total common stock reserved for future issuance		5,093,920		5,265,764

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Summary of Warrants Liability and Remeasured Liability to Estimated Fair Value

	December 3l,
	2017	2016
Risk-free interest rate	2.09%	1.93%
Expected volatility	100.39%	94.19%
Expected term	4.08 years	5.08 years
Expected dividend yield	0.0%	0.0%

Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

The following fair value hierarchy table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017:

	Fair Value Measurement as of December 31, 2017
	Level 1		Level 2		Level 3		Balance
Warrant liability	$	-	$	-	$	3,701,277	$	3,701,277
Total	$	-	$	-	$	3,701,277	$	3,701,277

Summary of Reconciliation of Warrant Liability Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs

	December 31,
	2017			2016
Beginning balance of warrant liability	$	4,095,019		$	-
Issuance of warrants		-			4,899,459
Change in fair value upon re-measurement		1,005,349			(597,615	)
Reclassification to Additional Paid-in Capital due to warrant amendment		-			(206,825	)
Reclassification to Additional Paid-in Capital due to warrant exercise		(1,399,091	)		-
Ending balance of warrant liability	$	3,701,277		$	4,095,019

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Reconciliation of Federal Statutory Income Tax Rate and Effective Income Tax Rate

A reconciliation of the federal statutory income tax rate and the effective income tax rate is as follows for the years ended December 31, 2017 and 2016:

	December 31,
	2017			2016
	(%)			(%)
Federal statutory rate		34			34
Warrant liability FMV adjustment		(8	)		6
Stock issuance costs	—				(5	)
Research and development credits		3			3
Removal of net operating loss and other credits		33			(33	)
Impact of federal tax rate change		(65	)	—
Stock compensation and other permanent items		3			(5	)
Effective income tax rate	—			—

Summary of Significant Components of Deferred Tax Assets

Significant components of the Company’s deferred tax assets at December 31, 2017 and 2016 are as follows:

	December 31,
	2017			2016
Acquired technology	$	103,000		$	201,000
Stock compensation expense		490,000			539,000
Accruals and other		216,000			130,000
Total deferred tax assets		809,000			870,000
Less valuation allowance		(809,000	)		(870,000	)
Net deferred tax assets	$	—		$	—

Summary of Changes in Amount of Unrecognized Tax Benefits (Excluding Interest and Penalties)

A summary of the changes in the amount of unrecognized tax benefits (excluding interest and penalties) for 2017 and 2016 are as follows:

	2017		2016
Beginning balance of unrecognized tax benefits	$	1,961,595	—
Additions based on tax positions of prior years	—		$	1,961,595
Ending balance of unrecognized tax benefits	$	1,961,595	$	1,961,595

Summarized Quarterly Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Summarized Quarterly Data

Summarized quarterly data for the years ended December 31, 2017 and 2016 are as follows:

	For the Quarters Ended
	March 31,			June 30,				September 30,			December 31,
2017
Research and development expense	$	770,686		$	2,017,569			$	2,717,698		$	1,631,540
General and administrative expense	$	1,209,570		$	871,979			$	984,047		$	1,027,594
Change in fair value of warrant liability	$	3,072,747		$	(1,261,912	)		$	1,544,138		$	(2,349,624	)
Net loss	$	(5,052,039	)	$	(1,625,969	)		$	(5,243,061	)	$	(308,443	)
Net loss per common share, basic⁽¹⁾	$	(0.37	)	$	(0.11	)		$	(0.34	)	$	(0.02	)
Net loss per common share, diluted⁽¹⁾	$	(0.37	)	$	(0.13	)	⁽²⁾	$	(0.34	)	$	(0.07	)
Weighted average shares outstanding, basic		13,528,311			15,343,325				15,351,295			15,368,610
Weighted average shares outstanding, diluted		13,528,311			15,420,954				15,351,295			15,503,583

2016
Research and development expense	$	2,015,076		$	2,095,149			$	1,339,343		$	1,502,032
General and administrative expense	$	1,137,753		$	802,655			$	830,092		$	822,325
Change in fair value of warrant liability	—			—				$	198,945		$	(796,560	)
Net loss	$	(3,225,409	)	$	(2,970,498	)		$	(3,025,281	)	$	(1,527,343	)
Net loss per common share, basic and diluted⁽¹⁾	$	(0.45	)	$	(0.41	)		$	(0.29	)	$	(0.12	)
Weighted average shares outstanding, basic and diluted		7,168,005			7,217,577				10,614,692			12,305,360

(1)	Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation.

(2)	Net loss per common share, diluted, for the quarter ended June 30, 2017 was revised from ($0.19) to ($0.13) to correct the computation of diluted loss per share under the treasury stock method. No adjustments were made to any other quarters.

Organization and Basis of Presentation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization And Basis Of Presentation [Abstract]
Month and year of incorporation	2007-01
Cash and cash equivalents	$ 7,679,267	$ 9,007,071	$ 8,691,155

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 Segment shares	Dec. 31, 2016 shares
Accounting Policies [Abstract]
Number of operating segment \| Segment	1
Shares of common stock subject to repurchase excluded from the weighted-average number of common stock outstanding	45,000	45,000
Dilutive shares related to the outstanding warrants	53,061	0

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	4,948,909	4,688,252
Common stock subject to repurchase [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	45,000	45,000
Warrants to purchase common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	2,744,500	3,323,876
Common stock options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	2,131,624	1,275,624
Employee stock purchase plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	27,785	43,752

Debt - Additional Information (Detail) - USD ($)		1 Months Ended		12 Months Ended
Debt - Additional Information (Detail) - USD ($)	Aug. 04, 2016	Jul. 31, 2016	May 31, 2014	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Repayment of principal and accrued interest					$ 4,500,000
Warrant exercise price per share				$ 3.46	$ 3.29
Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Loan and security agreement, interest incurred				$ 0	$ 148,500
Square 1 Bank [Member] \| Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Repayment of principal and accrued interest	$ 4,500,000
Line of credit facility, loan origination cost			$ 82,685
Debt instrument, unamortized discount	38,000
Warrants exercisable, stock issued					22,881
Warrant exercise price per share					$ 5.90
Square 1 Bank [Member] \| Loan and Security Agreement [Member] \| Warrants to purchase common stock [Member]
Debt Instrument [Line Items]
Debt instrument, unamortized discount	$ 59,000
Common stock shares issued upon conversion of warrants		9,887
Warrant value recorded in equity			$ 108,122

Commitments - Additional Information (Detail) - USD ($)	12 Months Ended
Commitments - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Lease commencement date	Jan. 01, 2017
Additional lease term	2 years
Lease expiry date	Dec. 31, 2018
Rent expense	$ 135,000	$ 116,000
Future minimum facility lease payments due in 2018	$ 139,000

Technology Acquisition Agreement - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	May 31, 2014	Jun. 30, 2007	Dec. 31, 2017
Technology Acquisition Agreement [Line Items]
Payment expensed as in-process research and development		$ 650,000
Mallinckrodt Plc [Member] \| Patented Technology [Member]
Technology Acquisition Agreement [Line Items]
Expected expiration of patent right			2030
Mallinckrodt Plc [Member] \| Rights and Patents Acquired from Questcor Pharmaceuticals Inc [Member] \| Maximum [Member]
Technology Acquisition Agreement [Line Items]
Milestone payments contingent amount			$ 51,500,000
Development Target One [Member] \| Rights and Patents Acquired from Questcor Pharmaceuticals Inc [Member]
Technology Acquisition Agreement [Line Items]
Milestone payment	$ 500,000
Development targets description			Upon the initiation of the first patient dosing in the Company's Phase 3 clinical trial for Gimoti.
Development Target Two And Three [Member] \| Mallinckrodt Plc [Member] \| Maximum [Member]
Technology Acquisition Agreement [Line Items]
Milestone payments contingent amount			$ 4,500,000
Development Target Two [Member] \| Mallinckrodt Plc [Member]
Technology Acquisition Agreement [Line Items]
Development targets description			Upon FDA's acceptance for review of a new drug application for Gimoti
Milestone payments contingent amount			$ 1,500,000
Development Target Three [Member] \| Mallinckrodt Plc [Member]
Technology Acquisition Agreement [Line Items]
Development targets description			Upon the FDA's approval of Gimoti
Milestone payments contingent amount			$ 3,000,000
Development Target Four [Member] \| Mallinckrodt Plc [Member] \| Patented Technology [Member]
Technology Acquisition Agreement [Line Items]
Development targets description			Depend on Gimoti's commercial success and will only apply if Gimoti receives regulatory approval. In addition, the Company will be required to pay to Mallinckrodt a low single digit royalty on net sales of Gimoti.
Milestone payments contingent amount			$ 47,000,000

Preferred Stock, Common Stock and Stockholders' Equity - Preferred Stock - Additional Information (Detail) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares outstanding	0	0

Preferred Stock, Common Stock and Stockholders' Equity - Common Stock - Additional Information (Detail) - USD ($)							2 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2018	Feb. 16, 2017	Dec. 15, 2016	Aug. 03, 2016	Jul. 25, 2016	Apr. 15, 2016	Mar. 31, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2017
Sale Of Stock [Line Items]
Common stock, shares outstanding									15,413,610	12,350,360
Shareholders voting power description									Each share of common stock is entitled to one vote. The holders of the common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors of the Company.
Dividends declared on common stock									$ 0
Common stock, shares issued									15,413,610	12,350,360
Weighted average exercise price of warrants									$ 3.46	$ 3.29
Proceeds from issuance of common stock, net									$ 7,389,101	$ 354,855
July 2016 Financing [Member]
Sale Of Stock [Line Items]
Common stock, shares issued					1,804,512
Purchase price of common stock					$ 2.49375
Unregistered warrants to purchase of common stock		526,315							2,449,129
Weighted average exercise price of warrants		$ 2.41
Aggregate gross proceeds from sale of common stock and warrants					$ 4,500,000
Aggregate net proceeds from sale of common stock and warrants					$ 4,000,000
Reclassification of warrant liability to Additional Paid-in Capital		$ 1,400,000
Common stock shares issued upon conversion of warrants		211,860
July Warrants [Member]
Sale Of Stock [Line Items]
Warrants exercisable, stock issued					0.75
Unregistered warrants to purchase of common stock					1,353,384
Weighted average exercise price of warrants					$ 2.41
Warrants expiration date					Jan. 25, 2022
July Wainwright Warrants [Member]
Sale Of Stock [Line Items]
Unregistered warrants to purchase of common stock					90,226
Weighted average exercise price of warrants					$ 3.1172
Warrants expiration date					Jul. 21, 2021
August 2016 Financing [Member]
Sale Of Stock [Line Items]
Common stock, shares issued				3,244,120
Purchase price of common stock				$ 3.0825
Aggregate gross proceeds from sale of common stock and warrants				$ 10,000,000
Aggregate net proceeds from sale of common stock and warrants				$ 9,200,000
August Warrants [Member]
Sale Of Stock [Line Items]
Warrants exercisable, stock issued				0.5
Unregistered warrants to purchase of common stock				1,622,060
Weighted average exercise price of warrants				$ 3.03
Warrants expiration date				Feb. 03, 2022
August Wainwright Warrants [Member]
Sale Of Stock [Line Items]
Unregistered warrants to purchase of common stock				162,206
Weighted average exercise price of warrants				$ 3.853125
Warrants expiration date				Jul. 29, 2021
2016 Financings [Member]
Sale Of Stock [Line Items]
Common stock, shares issued								5,048,632
Aggregate gross proceeds from sale of common stock and warrants								$ 14,500,000
2016 Financings [Member] \| Warrant Liability [Member]
Sale Of Stock [Line Items]
Total initial fair value of warrants issued									$ 4,899,459
Warrant Amendments [Member]
Sale Of Stock [Line Items]
Unregistered warrants to purchase of common stock			252,432
Amendment Date			Dec. 15, 2016
Reclassification of warrant liability to Additional Paid-in Capital			$ 207,000
Underwritten Public Offering [Member]
Sale Of Stock [Line Items]
Purchase price of common stock							$ 2.90
Common stock shares issues							2,775,861
Gross proceeds from public offering of common stock							$ 8,000,000
Proceeds from issuance of common stock, net							$ 7,300,000
FBR Sales Agreement [Member]
Sale Of Stock [Line Items]
Common stock, shares issued										56,000
Proceeds from issuance of common stock, net										$ 296,000
Common stock, shares issuable						649,074
Common stock , weighted average price per share										$ 5.45
FBR Sales Agreement [Member] \| Maximum [Member]
Sale Of Stock [Line Items]
Common stock, value of shares issuable											$ 16,000,000
Entity public float									$ 75,000,000
FBR Sales Agreement [Member] \| Subsequent Event [Member]
Sale Of Stock [Line Items]
Common stock, shares issued	79,758
Proceeds from issuance of common stock, net	$ 160,000
Common stock , weighted average price per share	$ 2.08
Proceeds from issuance of additional common stock	$ 11,900,000
Entity public float	$ 36,100,000
Entity public float, common stock shares	12,938,176
Common stock, closing price	$ 2.79

Preferred Stock, Common Stock and Stockholders' Equity - Summary of Warrants Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Warrants And Rights Note Disclosure [Abstract]
Warrants, Outstanding beginning balance	3,323,876
Warrants, Exercised	(526,315)
Warrants, Outstanding ending balance	2,797,561	3,323,876
Weighted Average Exercise Price, Outstanding beginning balance	$ 3.29
Weighted Average Exercise Price, Exercised	2.41
Weighted Average Exercise Price, Outstanding ending balance	$ 3.46	$ 3.29
Weighted Average Remaining Contractual Term (Years), Outstanding	3 years 11 months 8 days	4 years 11 months 15 days
Weighted Average Remaining Contractual Term (Years), Exercised	4 years 25 days

Preferred Stock, Common Stock and Stockholders' Equity - Equity Incentive Award Plans - Additional Information (Detail) - USD ($)		1 Months Ended	12 Months Ended
	Apr. 27, 2016	Feb. 29, 2016	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Aug. 31, 2013	May 31, 2007
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance			5,093,920	5,265,764
Options available for future grant			72,801	628,801
Number of stock options exchanged, outstanding			2,131,624	1,275,624
Unrecognized compensation costs			$ 1,700,000
Weighted average period			1 year 1 month 17 days
Intrinsic value, common stock price			$ 2.26	$ 2.02
Weighted Average Grant Date Fair Value Per Share, Granted			$ 1.87	$ 2.04
Options Granted [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, weighted average term			10 years
Number of stock options granted			856,000	414,000
Options Granted [Member] \| Minimum [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, vesting period			1 year
Options Granted [Member] \| Maximum [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, vesting period			4 years
2007 Equity Incentive Plan [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance				0			450,000
Issuance of common stock upon exercise of stock option, Shares			332,000
Stock options vested			287,000	287,000
Restricted shares to vest upon milestone achievement			45,000
Amended and Restated Equity Incentive Plan 2013 [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	4,786,425
Increase in number of shares of common stock reserved under the plan	500,000
Award plan expiration year	2026
2013 Equity Incentive Award Plan [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance						510,000
Additional common stock reserved for issuance			1,276,425
Shares of common stock available for issuance description			In addition, the number of shares of common stock available for issuance under the 2013 Plan will be annually increased on the first day of each fiscal year during the term of the 2013 Plan, beginning with the 2014 fiscal year, by an amount equal to the least of: (i) 300,000 shares; (ii) four percent of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year; or (iii) such other amount as the Company’s board of directors may determine.
Options available for future grant			72,801
2013 Equity Incentive Award Plan [Member] \| Annual Increase in Shares [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance			300,000
Reserve percentage for issuance of shares			4.00%
2013 Equity Incentive Award Plan [Member] \| Subsequent Event [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance					300,000
Options available for future grant					372,801
One-Time Option Exchange Program [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options exchanged		703,500
Number of stock options exchanged, outstanding		527,624
Number of stock options exchange percentage		75.00%
Options granted, vesting period		3 years
Stock options weighted average exercise price		$ 3.04
Incremental compensation expense during period under option exchange		$ 4,700
Unrecognized compensation costs		$ 141,000
Weighted average period		3 years

Preferred Stock, Common Stock and Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Outstanding beginning balance	1,275,624
Options, Outstanding ending balance	2,131,624	1,275,624
2007 Plan and 2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Outstanding beginning balance	1,275,624
Options, Granted	856,000
Options, Outstanding ending balance	2,131,624	1,275,624
Options, Vested and expected to vest at December 31, 2017	2,131,624
Options, Exercisable at December 31, 2017	1,111,270
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Outstanding beginning balance	$ 4.04
Weighted Average Exercise Price, Granted	2.45
Weighted Average Exercise Price, Outstanding ending balance	3.40	$ 4.04
Weighted Average Exercise Price, Vested and expected to vest at December 31, 2017	3.40
Weighted Average Exercise Price, Exercisable at December 31, 2017	$ 4.08
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding, Weighted Average Remaining Contractual Term [Abstract]
Weighted Average Remaining Contractual Term (Years), Outstanding	8 years 21 days	8 years 4 months 2 days
Weighted Average Remaining Contractual Term (Years), Granted	9 years 1 month 17 days
Weighted Average Remaining Contractual Term (Years), Vested and expected to vest at December 31, 2017	8 years 21 days
Weighted Average Remaining Contractual Term (Years), Exercisable at December 31, 2017	7 years 4 months 17 days
Share Based Compensation Arrangement by Share Based Payment Award Options Outstanding, Aggregate Intrinsic Value [Abstract]
Aggregate Intrinsic Value, Outstanding beginning balance	$ 191,160
Aggregate Intrinsic Value, Outstanding ending balance	219,480	$ 191,160
Aggregate Intrinsic Value, Vested and expected to vest at December 31, 2017	219,480
Aggregate Intrinsic Value, Exercisable at December 31, 2017	$ 219,480

Preferred Stock, Common Stock and Stockholders' Equity - Summary of Nonvested Options Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value Per Share, Granted	$ 1.87	$ 2.04
2007 Plan and 2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Options Nonvested, Outstanding beginning balance	690,961
Options, Granted	856,000
Options Vested	(526,607)
Options Nonvested, Outstanding ending balance	1,020,354	690,961
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value Per Share, Nonvested beginning balance	$ 3.34
Weighted Average Grant Date Fair Value Per Share, Granted	2.45
Weighted Average Grant Date Fair Value Per Share, Vested	3.22
Weighted Average Grant Date Fair Value Per Share, Nonvested ending balance	$ 2.65	$ 3.34

Preferred Stock, Common Stock and Stockholders' Equity - Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Detail) - USD ($)				12 Months Ended
	Jan. 01, 2018	May 03, 2017	Jun. 13, 2013	Dec. 31, 2017	Dec. 31, 2016	May 02, 2017
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs				$ 1,700,000
Weighted average period				1 year 1 month 17 days
Common stock reserved for issuance				5,093,920	5,265,764
Shares of common stock available for future issuance under ESPP				91,934	37,463
Stock issued during period, shares, period increase				220,000
Issuance of common stock under employee stock purchase plan				75,529	34,067
Payroll withholdings from employees				$ 135,000	$ 99,000
Amended and Restated ESPP [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		1,250,000
Increase in number of shares of common stock reserved under the plan		100,000
Number of shares increased annually to common stock shares reserved for issuance		100,000				30,000
Award plan expiration year		2027
Employee stock purchase plan [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of common stock as percentage of fair market value			85.00%
Percentage of deduction of eligible compensation			20.00%
Common stock reserved for issuance			30,000
Shares of common stock available for issuance description				In addition, the number of shares of common stock available for issuance under the ESPP has been annually increased on the first day of each fiscal year during the term of the ESPP by an amount equal to the lesser of: (i) 30,000 shares; (ii) one percent of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year; or (iii) such other amount as the Company’s board of directors may determine.
Reserve percentage for issuance of shares			1.00%
ESPP approval date			Aug. 29, 2013
Subsequent Event [Member] \| Employee stock purchase plan [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	191,934
Stock issued during period, shares, period increase	100,000

Preferred Stock, Common Stock and Stockholders' Equity - Summary of Estimated Fair Value of Employee Stock Purchase Plan Award (Detail) - Employee stock purchase plan [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate, minimum	0.79%	0.47%
Risk free interest rate, maximum	1.10%	0.50%
Expected term	6 months	6 months
Expected volatility of common stock, minimum	37.60%	83.83%
Expected volatility of common stock, maximum	99.23%	212.80%
Expected dividend yield	0.00%	0.00%

Preferred Stock, Common Stock and Stockholders' Equity - Summary of Estimated Fair Value of Stock Option Award (Detail) - Common stock options [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate, minimum	1.93%	1.25%
Risk free interest rate, maximum	2.16%	1.58%
Expected volatility of common stock, minimum	94.05%	74.44%
Expected volatility of common stock, maximum	98.23%	75.91%
Expected dividend yield	0.00%	0.00%
Minimum [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected option term	5 years 6 months	5 years 3 months 18 days
Maximum [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected option term	6 years	6 years

Preferred Stock, Common Stock and Stockholders' Equity - Summary of Recognized Non-Cash Stock-Based Compensation Expense (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,819,431	$ 1,706,524
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	819,815	698,032
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 999,616	$ 1,008,492

Preferred Stock, Common Stock and Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock options issued and outstanding	2,131,624	1,275,624
Authorized for future option grants	72,801	628,801
Warrants to purchase common stock	2,797,561	3,323,876
Authorized for employee stock purchase plan	91,934	37,463
Total common stock reserved for future issuance	5,093,920	5,265,764

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock, shares issued		15,413,610	12,350,360
Transfers of assets out of Level 1 into Level 2		$ 0
Transfers of assets out of Level 2 into Level 1		0
Transfers of liabilities out of Level 1 into Level 2		0
Transfers of liabilities out of Level 2 into Level 1		0
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		0
Liabilities		0
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		0
Liabilities		$ 0
2016 Financings [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock, shares issued	5,048,632
Aggregate gross proceeds from sale of common stock and warrants	$ 14,500,000
2016 Financings [Member] \| Maximum [Member] \| Common Stock Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants to purchase of common stock	2,975,444
Underwriters [Member] \| Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants to purchase of common stock	252,432

Fair Value Measurements - Summary of Warrants Liability and Remeasured Liability to Estimated Fair Value (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Risk-free interest rate	2.09%	1.93%
Expected volatility	100.39%	94.19%
Expected term	4 years 29 days	5 years 29 days
Expected dividend yield	0.00%	0.00%

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value Measurement, Recurring [Member]	Dec. 31, 2017 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities fair value	$ 3,701,277
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities fair value	3,701,277
Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities fair value	3,701,277
Warrant Liability [Member] \| Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total liabilities fair value	$ 3,701,277

Fair Value Measurements - Summary of Reconciliation of Warrant Liability Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) - Fair Value Measurement, Recurring [Member] - Warrant Liability [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 4,095,019
Issuance of warrants		$ 4,899,459
Change in fair value upon re-measurement	1,005,349	(597,615)
Reclassification to Additional Paid-in Capital due to warrant amendment		(206,825)
Reclassification to Additional Paid-in Capital due to warrant exercise	(1,399,091)
Ending balance	$ 3,701,277	$ 4,095,019

Employee Benefit Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Eligible age for employees for participating in the plan	21 years
Company's contributions to employee benefit plan	$ 0	$ 3,700
Future
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to employee benefit plan	$ 3,500

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Accrual on interest and penalties related to income taxes	$ 0	$ 0
Unrecognized tax benefits	1,961,595	1,961,595	$ 1,961,595
Reduction in income tax expense upon enactment of Tax Cuts and Jobs Act	7,900,000
Removal of net operating losses from deferred tax assets	15,900,000	$ 15,900,000
Cumulative change in ownership for limitation of use of net operating loss and research and development credit carryforwards		50.00%
Period of cumulative change of ownership		3 years
Removal of research and development credit from deferred tax assets	3,000,000	$ 3,000,000
Percentage of taxable income offset by tax losses		80.00%
Unrecognized tax benefits that would affect company's effective tax rate, if recognized	0	$ 0
Unrecognized tax benefits, period increase (decrease)		0
Unrecognized tax benefits, interest and penalties expense		$ 0
Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax years subject to examination by taxing authorities		2007
California [Member]
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	1,900,000	$ 1,900,000
Net operating loss carry forwards	41,700,000	41,700,000
Expiry date of carry forwards			Dec. 31, 2017
Tax credit carry forwards	1,200,000	1,200,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	61,900,000	$ 61,900,000
Expiry date of carry forwards		Dec. 31, 2027
Tax credit carry forwards	$ 2,000,000	$ 2,000,000

Income Taxes - Reconciliation of Federal Statutory Income Tax Rate and Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory rate	34.00%	34.00%
Warrant liability FMV adjustment	(8.00%)	6.00%
Stock issuance costs		(5.00%)
Research and development credits	3.00%	3.00%
Removal of net operating loss and other credits	33.00%	(33.00%)
Impact of federal tax rate change	(65.00%)
Stock compensation and other permanent items	3.00%	(5.00%)

Income Taxes - Summary of Significant Components of Deferred Tax Assets (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Components Of Deferred Tax Assets [Abstract]
Acquired technology	$ 103,000	$ 201,000
Stock compensation expense	490,000	539,000
Accruals and other	216,000	130,000
Total deferred tax assets	809,000	870,000
Less valuation allowance	$ (809,000)	$ (870,000)

Income Taxes - Summary of Changes in Amount of Unrecognized Tax Benefits (Excluding Interest and Penalties) (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Additions based on tax positions of prior years	$ 1,961,595
Ending balance of unrecognized tax benefits	$ 1,961,595

Summarized Quarterly Data (Unaudited) - Summarized Quarterly Data (Detail) - USD ($)	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
Quarterly Financial Information Disclosure [Abstract]
Research and development expense	$ 1,631,540	$ 2,717,698	$ 2,017,569	$ 770,686	$ 1,502,032	$ 1,339,343	$ 2,095,149	$ 2,015,076	$ 7,137,493	$ 6,951,600
General and administrative expense	1,027,594	984,047	871,979	1,209,570	822,325	830,092	802,655	1,137,753	4,093,189	3,592,825
Change in fair value of warrant liability	(2,349,624)	1,544,138	(1,261,912)	3,072,747	(796,560)	198,945			1,005,349	(597,615)
Net loss	$ (308,443)	$ (5,243,061)	$ (1,625,969)	$ (5,052,039)	$ (1,527,343)	$ (3,025,281)	$ (2,970,498)	$ (3,225,409)	$ (12,229,512)	$ (10,748,531)
Net loss per common share, basic	$ (0.02)	$ (0.34)	$ (0.11)	$ (0.37)					$ (0.82)	$ (1.15)
Net loss per common share, diluted	$ (0.07)	$ (0.34)	$ (0.13)	$ (0.37)					$ (0.90)	$ (1.15)
Weighted average shares outstanding, basic	15,368,610	15,351,295	15,343,325	13,528,311					14,897,885	9,338,068
Weighted average shares outstanding, diluted	15,503,583	15,351,295	15,420,954	13,528,311					14,951,036	9,338,068
Net loss per common share, basic and diluted					$ (0.12)	$ (0.29)	$ (0.41)	$ (0.45)
Weighted average shares outstanding, basic and diluted					12,305,360	10,614,692	7,217,577	7,168,005

Summarized Quarterly Data (Unaudited) - Summarized Quarterly Data (Parenthetical) (Detail) - $ / shares	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Quarterly Financial Information [Line Items]
Revision in net loss per common share, diluted	$ (0.07)	$ (0.34)	$ (0.13)	$ (0.37)	$ (0.90)	$ (1.15)
Computation of Diluted Loss Per Share Under Treasury Stock Method [Member]
Schedule Of Quarterly Financial Information [Line Items]
Revision in net loss per common share, diluted			(0.13)
Computation of Diluted Loss Per Share Under Treasury Stock Method [Member] \| Scenario, Previously Reported [Member]
Schedule Of Quarterly Financial Information [Line Items]
Revision in net loss per common share, diluted			$ (0.19)