Viking Therapeutics (VKTX) 10-Q 9 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	VKTX
Entity Registrant Name	Viking Therapeutics, Inc.
Entity Central Index Key	1,607,678
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		50,933,195

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 36,356	$ 8,988
Short-term investments – available for sale	41,112	11,587
Prepaid clinical trial and preclinical study costs	1,014	887
Prepaid expenses and other current assets	249	389
Total current assets	78,731	21,851
Deferred public offering and other financing costs	240	270
Total assets	78,971	22,121
Current liabilities:
Accounts payable	658	1,529
Other accrued liabilities	1,889	2,257
Accrued interest, current	34	22
Convertible notes payable, current (net of discount of $146 and $404 at March 31, 2018 and December 31, 2017, respectively)	3,721	3,451
Debt conversion feature liability, current	37	1,398
Total current liabilities	6,339	8,657
Total liabilities	6,339	8,657
Commitments and contingencies (Note 8)
Stockholders’ equity:
Preferred stock, $0.00001 par value: 10,000,000 shares authorized at March 31, 2018 and December 31, 2017; no shares issued and outstanding at March 31, 2018 and December 31, 2017
Common stock, $0.00001 par value: 300,000,000 shares authorized at March 31, 2018 and December 31, 2017; 50,933,195 and 35,817,104 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	1
Additional paid-in capital	157,146	94,339
Accumulated deficit	(84,406)	(80,855)
Accumulated other comprehensive loss	(109)	(20)
Total stockholders’ equity	72,632	13,464
Total liabilities and stockholders’ equity	$ 78,971	$ 22,121

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Convertible notes payable, discount, current portion	$ 146	$ 404
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	50,933,195	35,817,104
Common stock, shares outstanding	50,933,195	35,817,104

Statements of Operations and Co

Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenues	$ 0	$ 0
Operating expenses:
Research and development	3,043	3,528
General and administrative	1,762	1,441
Total operating expenses	4,805	4,969
Loss from operations	(4,805)	(4,969)
Other income (expense):
Change in fair value of debt conversion feature liability	1,361	278
Amortization of debt discount	(258)	(431)
Amortization of financing costs	(30)	(98)
Interest income (expense), net	181	(2)
Total other income (expense), net	1,254	(253)
Net loss	(3,551)	(5,222)
Other comprehensive loss, net of tax:
Unrealized loss on securities	(89)	(1)
Comprehensive loss	$ (3,640)	$ (5,223)
Net loss per common share
Basic	$ (0.08)	$ (0.23)
Diluted	$ (0.10)	$ (0.23)
Weighted-average shares used to compute net loss per share
Basic	44,648,799	22,352,921
Diluted	45,305,515	22,352,921

Statements of Cash Flows (Unaud

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net loss	$ (3,551)	$ (5,222)
Adjustments to reconcile net loss to net cash used in operating activities
Amortization of debt discount on notes payable	258	431
Amortization of investment premiums	62	31
Amortization of financing costs	30	98
Amortization of non-cash clinical trial costs	225	42
Change in fair value of debt conversion feature liability	(1,361)	(278)
Stock-based compensation	610	402
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(316)	221
Accounts payable	(832)	523
Accrued expenses	(428)	472
Net cash used in operating activities	(5,303)	(3,280)
Cash flows from investing activities
Purchases of investments	(32,279)	(6,057)
Proceeds from maturities of investments	2,652	8,096
Net cash (used in) provided by investing activities	(29,627)	2,039
Cash flows from financing activities
Proceeds from issuances of common stock, net of underwriting discounts and commissions	58,822	2,540
Public offering and financing costs	(146)	(16)
Proceeds from warrant and option exercises	3,622
Net cash provided by financing activities	62,298	2,524
Net increase in cash and cash equivalents	27,368	1,283
Cash and cash equivalents beginning of period	8,988	3,076
Cash and cash equivalents end of period	36,356	4,359
Supplemental disclosure of non-cash investing and financing transactions
Shares issued to cover future clinical trial costs		1,800
Unpaid deferred public offering and other financing costs	$ 136	$ 16

Organization, Liquidity and Man

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies	1. Organization, Liquidity and Management’s Plan, and Summary of Significant Accounting Policies The Company Viking Therapeutics, Inc., a Delaware corporation (the “Company”), is a clinical-stage biopharmaceutical company focused on the development of novel therapies for metabolic and endocrine disorders. The Company was incorporated under the laws of the State of Delaware on September 24, 2012 and its principal executive offices are located in San Diego, California. Basis of Presentation The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying balance sheet as of March 31, 2018, statements of operations for the three months ended March 31, 2018 and 2017 and statements of cash flows for the three months ended March 31, 2018 and 2017 are unaudited. These unaudited financial statements have been prepared in accordance with the rules and regulations of the United States Securities and Exchange Commission (“SEC”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. These financial statements should be read in conjunction with the audited financial statements and the accompanying notes for the year ended December 31, 2017 contained in the Annual Report on Form 10-K filed by the Company with the SEC on March 7, 2018. The unaudited interim financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments (consisting of normal recurring adjustments) necessary to state fairly the Company’s financial position as of March 31, 2018, the results of operations for the three months ended March 31, 2018 and 2017 and cash flows for the three months ended March 31, 2018 and 2017. The December 31, 2017 balance sheet included herein was derived from the audited financial statements, but does not include all disclosures or notes required by GAAP for complete financial statements. The financial data and other information disclosed in these notes to the financial statements related to the three months ended March 31, 2018 and 2017 are unaudited. Interim results are not necessarily indicative of results for an entire year. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying financial statements. Significant estimates made in preparing these financial statements relate to determining the fair value of the debt conversion feature liability and accounting for certain commitments. Actual results could differ from those estimates. Recent Accounting Pronouncements Adopted Accounting Standards In May 2014, the FASB issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. The FASB has subsequently issued the following amendments to ASU No. 2014-09, which have the same effective date and transition date of January 1, 2018: • In August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers • In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers • In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers • In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers • In December 2016, the FASB issued ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, which amends certain narrow aspects of the guidance issued in ASU No. 2014-09 including guidance related to the disclosure of remaining performance obligations and prior-period performance obligations, as well as other amendments to the guidance on loan guarantee fees, contract costs, refund liabilities, advertising costs and the clarification of certain examples. The Company evaluated the potential impact that these standards had on its financial position and results of operations. There is no current impact of this new guidance on its financial statements as the Company does not currently have any revenue generating arrangements. In August 2016, the FASB issued ASU No. 2016-15, Classification of Certain Cash Receipts and Cash Payments The Company’s adoption of ASU 2016-15 on January 1, 2018 did not have a material effect on its financial statements and related disclosures. Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases for the Company in the first quarter of fiscal year 2019 and early adoption is permitted. ASU 2016-02 is required to be applied with a modified retrospective approach and requires application of the new standard at the beginning of the earliest comparative period presented. The Company does not expect the adoption of ASU 2016-02 to have a material effect on its financial statements and related disclosures. In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments The Company is evaluating the effect that ASU 2016-13 will have on its financial statements and related disclosures. In July 2017, the FASB issued a two-part ASU No. 2017-11 , I. Accounting for Certain Financial Instruments with Down Round Features and II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception Cash and Cash Equivalents The Company considers all highly liquid investments with maturities of three months or less from the date of purchase to be cash equivalents. Investments Available-for-Sale Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive income (loss). The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. The amortization of premiums and accretion of discounts is included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. Concentration of Credit Risk Financial instruments, which potentially subject the Company to concentration of credit risk, consist primarily of cash and cash equivalents and marketable securities. The Company maintains deposits in federally insured depository institutions in excess of federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. Additionally, the Company has established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity. Prepaid Clinical Trial and Preclinical Study Costs Prepaid clinical trial and preclinical study costs represent advance payments by the Company for future clinical trial and preclinical study services to be performed by the clinical research organization and other research organizations. Such amounts are recognized as research and development expense as the related clinical trial and preclinical study services are performed. Deferred Financing Costs Deferred financing costs represent legal, accounting and other direct costs related to the Company’s efforts to raise capital through a public or private sale of the Company’s common stock. Costs related to public sales of the Company’s common stock are deferred until the completion of the applicable offering, at which time such costs are reclassified to additional paid-in-capital as a reduction of the proceeds. Costs related to private sales of the Company’s common stock are deferred until the completion of the applicable offering, at which time such costs are amortized over the term of the applicable purchase agreement. Revenue Recognition The Company has not recorded any revenues since its inception. However, in the future, the Company may enter into collaborative research and licensing agreements, under which the Company could be eligible for payments made in the form of upfront license fees, research funding, cost reimbursement, contingent event-based payments and/or royalties. On January 1, 2018, the Company adopted ASU 2014-09, Revenue from Contracts with Customers and all related amendments ("ASC 606" or "the new revenue standard"). ASC 606 is a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-s Research and Development Expenses All costs of research and development are expensed in the period incurred. Research and development costs primarily consist of fees paid to contract research organizations (“CROs”) and clinical trial sites, employee and consultant related expenses, which include salaries, benefits and stock-based compensation for research and development personnel, external research and development expenses incurred pursuant to agreements with third-party manufacturing organizations, facilities costs, travel costs, dues and subscriptions, depreciation and materials used in preclinical studies, clinical trials and research and development. The Company estimates its preclinical study and clinical trial expenses based on the services it received pursuant to contracts with research institutions and CROs that conduct and manage preclinical studies and clinical trials on the Company’s behalf. Clinical trial-related contracts vary significantly in length, and may be for a fixed amount, based on milestones or deliverables, a variable amount based on actual costs incurred, capped at a certain limit, or for a combination of these elements. The Company accrues service fees based on work performed, which relies on estimates of total costs incurred based on milestones achieved, patient enrollment and other events. The majority of the Company’s service providers invoice the Company in arrears, and to the extent that amounts invoiced differ from its estimates of expenses incurred, the Company accrues for additional costs. The financial terms of these agreements vary from contract to contract and may result in uneven expenses and payment flows. Preclinical study and clinical trial expenses include: • fees paid to CROs, consultants and laboratories in connection with preclinical studies; • fees paid to CROs, clinical trial sites, investigators and consultants in connection with clinical trials; and • fees paid to contract manufacturers and service providers in connection with the production, testing and packaging of active pharmaceutical ingredients and drug materials for preclinical studies and clinical trials. Payments under some of these agreements depend on factors such as the milestones accomplished, including enrollment of certain numbers of patients, site initiation and the completion of clinical trial milestones. To date, the Company has not experienced any events requiring it to make material adjustments to its accruals for service fees. If the Company does not identify costs that it has begun to incur or if it underestimates or overestimates the level of services performed or the costs of these services, its actual expenses could differ from its estimates which could materially affect its results of operations. Adjustments to the Company’s accruals are recorded as changes in estimates become evident. Furthermore, based on amounts invoiced to the Company by its service providers, the Company may also record payments made to those providers as prepaid expenses that will be recognized as expense in future periods as services are rendered. In May 2014, the Company entered into the Master License Agreement, pursuant to which it acquired certain rights to a number of research and development programs from Ligand Pharmaceuticals Incorporated, or Research and Development, Patent Costs Costs related to filing and pursuing patent applications are expensed as incurred to general and administrative expense, as recoverability of such expenditures is uncertain. Stock-Based Compensation The Company generally uses the straight-line method to allocate compensation cost to reporting periods over each optionee’s requisite service period, which is generally the vesting period, and estimates the fair value of stock-based awards or restricted stock units to employees and directors using the Black-Scholes option-valuation model. The Black-Scholes model requires the input of subjective assumptions, including volatility, the expected term and the fair value of the underlying common stock on the date of grant, among other inputs. For restricted stock and restricted stock unit awards, the Company generally uses the straight-line method to allocate compensation cost to reporting periods over the holder’s requisite service period, which is generally the vesting period, and uses the fair value at grant date to value the awards. For restricted stock that vests upon the satisfaction of certain performance conditions, the Company recognizes stock-based compensation expense when it becomes probable that the performance conditions will be met. At the point that it becomes probable that the performance conditions will be met, the Company records a cumulative catch-up of the expense from the grant date to the current date, and the Company then amortizes the remainder of the expense over the remaining service period. Income Taxes The Company accounts for its income taxes using the liability method whereby deferred tax assets and liabilities are determined based on temporary differences between the basis used for financial reporting and income tax reporting purposes. Deferred income taxes are provided based on the enacted tax rates in effect at the time such temporary differences are expected to reverse. A valuation allowance is provided for deferred tax assets if it is more likely than not that the Company will not realize those tax assets through future operations. ASC Topic 740-10, Income Taxes The Company’s policy is to recognize interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense. Net Loss per Common Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. The following table presents the computation of basic and diluted net loss per common share (in thousands, except per share data): Three Months Ended March 31, 2018 2017 Net Loss Net loss attributable to common stockholders - Basic $ (3,551 ) $ (5,222 ) Change in fair value of debt conversion feature liability (1,361 ) — Amortization of debt discount 258 — Interest expense 24 — Net loss attributable to common stockholders - Diluted $ (4,630 ) $ (5,222 ) Basic Shares Weighted-average common shares outstanding 44,893,895 22,660,017 Less: Weighted-average shares subject to repurchase (245,096 ) (307,096 ) Denominator for basic net loss per share 44,648,799 22,352,921 Diluted Shares Weighted-average common shares outstanding 44,893,895 22,660,017 Weighted-average shares subject to repurchase (245,096 ) (307,096 ) Effect of dilutive shares issuable upon conversion of debt 656,716 — Denominator for diluted net loss per share 45,305,515 22,352,921 Net loss per share: Basic $ (0.08 ) $ (0.23 ) Diluted $ (0.10 ) $ (0.23 ) Potentially dilutive securities that are not included in the calculation of diluted net loss per share because their effect is anti-dilutive are as follows (in common equivalent shares): As of March 31, 2018 2017 Common stock warrants 8,780,838 9,667,500 Restricted stock units 136,250 69,375 Common stock subject to repurchase 245,096 307,096 Common stock options 1,967,721 1,511,894 Shares issuable upon conversion of debt — 2,860,361 11,129,905 14,416,226 Segments The Company operates in only one segment. Management uses cash flows as the primary measure to manage its business and does not segment its business for internal reporting or decision making purposes.

Investments in Marketable Secur

Investments in Marketable Securities	3 Months Ended
	Mar. 31, 2018
Investments Debt And Equity Securities [Abstract]
Investments in Marketable Securities	2. Investments in Marketable Securities The Company’s investment strategy is focused on capital preservation. The Company invests in instruments that meet the credit quality standards outlined in the Company’s investment policy. This policy also limits the amount of credit exposure to any one issue or type of instrument. As of March 31, 2018 and December 31, 2017, the Company’s investments were in government money market funds, certificates of deposit and corporate debt securities. There were no sales of available-for-sale securities during the three months ended March 31, 2018 or during the year ended December 31, 2017. Investments classified as available-for-sale as of March 31, 2018 consisted of the following (in thousands): As of March 31, 2018 Amortized Cost Gross Unrealized Gains ( 1) Gross Unrealized Losses ( 1) Aggregate Estimated Fair Value Certificates of deposit ( 2) $ 250 $ — $ — $ 250 Corporate debt securities ( 2) 40,963 — (101 ) 40,862 $ 41,213 $ — $ (101 ) $ 41,112 (1) Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At March 31, 2018, there were no securities in an unrealized gain position and there were 56 securities in an unrealized loss position. These unrealized losses were less than $5,000 individually and $101,000 in the aggregate. These securities have not been in a continuous unrealized gain or loss position for more than 12 months. The Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis, which may be at maturity. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value. (2) At March 31, 2018, none of these securities were classified as cash and cash equivalents on the Company’s balance sheet and none of these securities were scheduled to mature outside of one year. Investments classified as available-for-sale as of December 31, 2017 consisted of the following (in thousands): As of December 31, 2017 Amortized Cost Gross Unrealized Gains ( 1) Gross Unrealized Losses ( 1) Aggregate Estimated Fair Value Certificates of deposit ( 2) $ 249 $ — $ — $ 249 Corporate debt securities ( 2) 11,357 — (19 ) 11,338 $ 11,606 $ — $ (19 ) $ 11,587 (1) Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At December 31, 2017, there were 29 securities in an unrealized loss position. These unrealized losses were less than $3,000 individually and $19,000 in the aggregate. These securities have not been in a continuous unrealized loss position for more than 12 months. The Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis, which may be at maturity. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value. ( 2 ) At December 31, 2017, none of these securities were classified as cash and cash equivalents on the Company’s balance sheet and none of these securities were scheduled to mature outside of one year.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments The Company’s financial instruments consist of cash and cash equivalents, investments, accounts payable, debt and its related debt conversion feature liability. The carrying amounts reported in the accompanying balance sheets for cash and cash equivalents and accounts payable approximate fair value because of the short-term maturity of those instruments. Further, the Company believes the fair value of the debt approximates its carrying value based on relatively stable interest rates and short-term maturity of this instrument. Fair value measurements are classified and disclosed in one of the following three categories: Level 1 —Quoted prices in active markets for identical assets or liabilities. Level 2 —Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. As of March 31, 2018 and December 31, 2017, all of the Company’s financial assets that were subject to fair value measurements were valued using observable inputs. The Company’s financial assets valued based on Level 1 inputs consist of money market funds and certificates of deposit. The Company’s financial assets valued based on Level 2 inputs consist of corporate debt securities, which consist of investments in highly-rated investment-grade corporations. The Company’s financial liability that was subject to fair value measurement consisted of a debt conversion feature that has been recorded as a liability based on Level 3 unobservable inputs. The fair value of the debt conversion feature, current as of March 31, 2018 and December 31, 2017 required management to estimate fair value based on the Black-Scholes-Merton option valuation model. The Black-Scholes-Merton option valuation model was adopted as a result of the Company’s entry in January 2016 into the the conversion terms of the Secured Convertible Promissory Note (“ the Loan and Security Agreement. The debt conversion feature embedded in each tranche of the Ligand Note is accounted for under ASC Topic 815 – Derivatives and Hedging The Company’s investment strategy is focused on capital preservation. The Company invests in instruments that meet the credit quality standards outlined in the Company’s investment policy. This policy also limits the amount of credit exposure to any one issue or type of instrument. As of March 31, 2018, the Company’s investments were in government money market funds, certificates of deposit and corporate debt securities. The fair values of the Company’s financial instruments are presented below (in thousands): Fair Value Measurements at March 31, 2018 Total Level 1 Level 2 Level 3 Financial assets carried at fair value: Cash equivalents: Government money market funds $ 21,876 $ 21,876 $ — $ — Corporate debt securities, available-for-sale 15,777 — 15,777 — Short-term investments Certificates of deposit, available-for-sale 250 — 250 — Corporate debt securities, available-for-sale 40,862 — 40,862 — Total financial assets $ 78,765 $ 21,876 $ 56,889 $ — Financial liabilities carried at fair value: Debt conversion feature - current $ 37 $ — $ — $ 37 Total financial liabilities $ 37 $ — $ — $ 37 Fair Value Measurements at December 31, 2017 Total Level 1 Level 2 Level 3 Financial assets carried at fair value: Cash equivalents: Government money market funds $ 6,361 $ 6,361 $ — $ — Corporate debt securities, available-for-sale 1,244 — 1,244 — Short-term investments Certificates of deposit, available-for-sale 249 — 249 — Corporate debt securities, available-for-sale 11,338 — 11,338 — Total financial assets $ 19,192 $ 6,361 $ 12,831 $ — Financial liabilities carried at fair value: Debt conversion feature - current $ 1,398 $ — $ — $ 1,398 Total financial liabilities $ 1,398 $ — $ — $ 1,398 The table below presents a summary of changes in the Company’s debt conversion feature liability measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the three months ended March 31, 2018 and 2017 (in thousands): Three Months Ended March 31, 2018 2017 Debt conversion feature: Beginning balance $ 1,398 $ 731 Adjustments resulting from changes in fair value recognized in earnings (1,361 ) (278 ) Ending balance $ 37 $ 453 The following table sets forth the Company’s valuation techniques and significant unobservable inputs used to determine fair value for significant Level 3 liabilities (in thousands, except for volatility and risk free rate): Fair Value Significant Assets Liabilities Valuation Technique(s) Unobservable Input % Debt conversion feature liability March 31, 2018 $ — $ 37 Black-Scholes-Merton option valuation model Volatility 63% Risk Free Rate 1.68% December 31, 2017 $ — $ 1,398 Black-Scholes-Merton option valuation model Volatility 100% Risk Free Rate 1.46% Level 3 Fair Value Sensitivity Debt Conversion Feature Liability As of March 31, 2018 and December 31, 2017, the fair value of the debt conversion feature liability includes the estimated volatility and risk free rate. The higher/lower the estimated volatility, the higher/lower the value of the debt conversion feature liability. The higher/lower the risk free interest rate, the higher/lower the value of the debt conversion feature liability.

Convertible Notes Payable

Convertible Notes Payable	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Convertible Notes Payable	4 . Convertible Notes Payable Convertible notes payable consisted of the following (in thousands): March 31, December 31, 2018 2017 Current maturities: Convertible note payable issued during 2014 to Ligand pursuant to the Master License Agreement with a 5% annual interest rate, due during 2016 (amended in January 2016 to a 2.5% annual interest rate with maturity extended to 2017, and subsequently amended in May 2017 with maturity extended to May 21, 2018) $ 1,917 $ 1,917 Conversion payoff value 1,950 1,938 Discount on notes payable, current (146 ) (404 ) Convertible notes payable, current (net of discount) $ 3,721 $ 3,451 Pursuant to the Loan and Security Agreement, among other things, Ligand provided the Company with loans in the aggregate amount of $2.5 million. Up until January 21, 2016, the principal amount outstanding under the loans accrued interest at a fixed per annum rate equal to the lesser of 5.0% or the maximum interest rate permitted by law. Effective as of January 22, 2016, the principal amount outstanding under the loans accrue interest at a fixed per annum rate equal to the lesser of 2.5% or the maximum interest rate permitted by law. In the event the Company defaults under the loans, the loans will accrue interest at a fixed per annum rate equal to the lesser of 8% or the maximum interest rate permitted by law. The loans are evidenced by the Ligand Note. Pursuant to the terms of the Loan and Security Agreement and the Ligand Note, the loans will become due and payable upon the written demand of Ligand at any time after the earlier to occur of an event of default under the Loan and Security Agreement or the Ligand Note, or May 21, 2018 (the “Maturity Date”), unless the loans are repaid in cash or converted into equity prior to such time. In addition, under the Loan and Security Agreement, the Company may not declare or pay dividends in respect of its common stock without Ligand’s prior written consent. Additionally, pursuant to the terms of the Loan and Security Agreement, upon the consummation of the Company’s first bona fide capital financing transaction occurring after January 22, 2016, but prior to the Maturity Date, with aggregate net proceeds to the Company of at least $2.0 million (the “Next Financing”), the Company was required to repay $1.5 million of the Ligand Note obligation to Ligand, with at least $300,000 of such payment to be paid in cash (with any greater cash amount determined by the Company in its sole and absolute discretion), and the balance of the $1.5 million payment (the “Balance”) to be paid in the form of such number of shares of the Company’s equity securities that are issued in the Next Financing as is equal to the quotient obtained by dividing the Balance by the lesser of (1) the lowest price per share paid by investors in the Next Financing (the “Financing Price”), and (2) $8.00 (subject to adjustment for stock dividends, splits, combinations or similar transactions). Each $1.00 of the $1.5 million payment reduced the amount of accrued and unpaid interest and then unpaid principal amount of the loans under the Ligand Note by $0.50. As a result of an amendment to the Loan and Security Agreement entered into on January 22, 2016, which amended the conversion terms of the Ligand Note , beginning with the quarter ended March 31, 2016, management adopted the Black-Scholes-Merton option valuation model for the Ligand Note, resulting in a debt modification adjustment of $576,000 to the debt conversion feature liability, offset with an adjustment recorded to the Ligand Note discount and conversion payoff value. On April 13, 2016, the Company completed an underwritten public offering of its common stock and warrants to purchase shares of its common stock (the “Offering”) resulting in net proceeds of $7.8 million, after deducting underwriting discounts, commissions and other offering expenses of $1.6 million. The Offering constituted a Next Financing under the Loan and Security Agreement; therefore, the Company repaid $1.5 million of the Ligand Note with $300,000 paid in cash and $1.2 million paid in the form of 960,000 shares of its common stock (the “Ligand Shares”) and a warrant to purchase up to 960,000 shares of Company’s common stock (the “Ligand Warrant”). The Ligand Warrant has an exercise price of $1.50 per share of common stock, was immediately exercisable upon issuance and will expire on April 13, 2021. On May 8, 2017, the Company entered into the Third Loan Amendment to the Loan and Security Agreement (the “Third Loan Amendment”), which, (1) extended the maturity date of the Loans from May 21, 2017 to May 21, 2018, and (2) provided that the Company was required to repay $200,000 of the Ligand Note in the third quarter of 2017, which payment had to be made solely in cash (the “Required Repayment”). The Company made the Required Repayment on July 13, 2017. The Required Repayment was applied, first, to accrued and unpaid interest on the Loans and, second, to the unpaid principal amount of the Loans. Each $1.00 of value of the Required Repayment reduced the amount of accrued and unpaid interest and then unpaid principal amount on the Loans by $0.50. As a result of the Third Loan Amendment, the Company recorded a debt modification adjustment of $1.0 million to the debt conversion feature liability primarily due to the longer expected term, offset with an adjustment recorded to the Ligand Note discount. In addition, the Company may repay any portion of the outstanding principal amount of the loans under the Ligand Note, plus accrued and previously unpaid interest thereon, by delivering a notice to Ligand (the “Additional Repayment Notice”), specifying the amount that the Company wishes to repay (the “Additional Payment Amount”). Ligand will have five days to elect to receive the Additional Payment Amount in cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock. If Ligand does not make an election within such five-day period, the form of the Additional Payment Amount will be at the Company’s sole election and discretion, subject to the number of shares of common stock being reduced to the extent that the issuance of shares would increase Ligand’s beneficial ownership of the Company’s common stock to greater than 49.9%. To the extent that any portion of an Additional Payment Amount will be paid in the form of shares of the Company’s common stock, the number of shares issuable will be equal to the quotient obtained by dividing the portion of the Additional Payment Amount that will be paid in shares by the lesser of (1) (a) if the Company delivers the Additional Repayment Notice within 180 days of the closing of the Next Financing, the Financing Price, or (b) if the Company delivers the Additional Repayment Notice 180 days or more after the closing of the Next Financing, the volume weighted average closing price of the Company’s common stock for the 30 days prior to the date the Company delivers the Additional Repayment Notice, and (2) $8.00 (subject to adjustment for stock dividends, splits, combinations or similar transactions). Each $1.00 of any Additional Repayment Amount will reduce the amount of accrued and unpaid interest and then unpaid principal amount under the Ligand Note by $0.50. Following the Maturity Date, Ligand may demand repayment of the loans under the Ligand Note in full. If (1) the Ligand Note is not repaid in full prior to the Maturity Date and Ligand demands repayment, or (2) the Company wishes to repay the full amount owed under the Ligand Note prior to the Maturity Date, the Company will be obligated to repay to Ligand an amount equal to 200% of the aggregate of the outstanding principal amount of the loans under the Ligand Note and of all accrued and unpaid interest thereon (the “Remaining Balance”). In either case, the Company may, at its sole election and discretion, elect to pay the Remaining Balance solely in cash. If the Company does not elect to repay the Remaining Balance in cash, the form of payment and mix of cash and shares of the Company’s common stock will be at Ligand’s sole election and discretion. To the extent that any portion of the Remaining Balance will be paid in the form of shares of the Company’s common stock, the number of shares issuable will be equal to the quotient obtained by dividing the portion of the Remaining Balance that will be paid in shares by the lesser of (1) the volume weighted average closing price of the Company’s common stock for the 30 days prior to the date of Ligand’s demand for repayment or the date of the Company’s prepayment of the Remaining Balance in full, and (2) $8.00 (subject to adjustment for stock dividends, splits, combinations or similar transactions). In connection with the Loan and Security Agreement, the Company also granted Ligand a continuing security interest in all of its right, title and interest in and to its assets as collateral for the full, prompt, complete and final payment and performance when due of all obligations under the Loan and Security Agreement and the Ligand Note. During the three months ended March 31, 2018, the Company recorded $24,000 of interest expense, $258,000 of amortization of debt discount, and $1.4 million as other income related to the decrease in the fair value of the debt conversion feature liability. During the three months ended March 31, 2017, the Company recorded $24,000 of interest expense, $431,000 of amortization of debt discount and $278,000 as other income related to the decrease in the fair value of the debt conversion feature liability.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Stockholders' Equity	5. Stockholders’ Equity Preferred Stock The Company is authorized to issue up to 10,000,000 shares of preferred stock, $0.00001 par value per share, with no shares outstanding as of March 31, 2018 and December 31, 2017. The Board of Directors is authorized to designate the terms and conditions of any preferred stock the Company may issue without further action by the stockholders of the Company. Common Stock The Company is authorized to issue up to 300,000,000 shares of common stock, $0.00001 par value per share. In February 2014, the Company entered into a stock purchase agreement with one of its founders. The agreement provided for the purchase of 1,000,000 shares of the Company’s common stock at a price per share of $0.01 in exchange for future services to be rendered to the Company as measured by certain performance criteria. The shares were subject to a repurchase option and were to vest in two tranches of 500,000 shares each, upon achievement of the performance target or upon a triggering event as defined. The Company determined that the fair value of the unrecognized expense was $168,000 at February 20, 2014, the grant date. In May 2015, the Company repurchased 633,810 of these shares at a purchase price of $0.00001 per share. In connection with the repurchase, the Company entered into an amendment to the stock purchase agreement to provide that the remaining 366,190 shares will continue to vest in two tranches of 183,095 shares each, upon achievement of the performance target or upon a triggering event as defined. The pro rata grant date fair value of the unrecognized expense is $62,000. In October 2015, a triggering event became probable of occurrence and was deemed achieved in October 2016; therefore, the Company recorded $31,000 of stock-based compensation expense through December 31, 2016. No similar expense was recognized during the three months ended March 31, 2018 and 2017. The Company will continue to reassess at each reporting period whether it is probable that the performance target will be achieved, and if and when it is deemed probable, the Company will begin to record compensation expense using the fair value to determine stock-based compensation expense in its financial statements over the period the Company estimates the performance target will actually be achieved. On June 20, 2016, the Company entered into the Equity Distribution Agreement (the “Distribution Agreement”) with Maxim Group LLC (“Maxim”) pursuant to which the Company was able to offer and sell, from time to time, through Maxim up to 3,748,726 shares of its common stock (the “Maxim Offering”). Effective July 26, 2017, the Distribution Agreement terminated automatically in accordance with the terms thereof. All shares of common stock offered and sold in the Maxim Offering were issued pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-212134) filed with the SEC on June 20, 2016, as amended by Amendment No. 1 thereto filed with the SEC on July 26, 2016, and declared effective on July 26, 2016 (the “Shelf Registration Statement”) and the prospectus relating to the Maxim Offering that forms a part of the registration statement on Form S-3. The registration statement on Form S-3 was declared effective by the SEC on July 26, 2016. From the inception of the Distribution Agreement through July 26, 2017, the Company sold 1,267,237 shares of its common stock under the Distribution Agreement resulting in net proceeds to the Company of $1.6 million, after deducting the sales agent’s commission. On August 24, 2016, the Company entered into a common stock purchase agreement (the “Purchase Agreement”), pursuant to which Aspire Capital Fund, LLC (“Aspire Capital”) was committed to purchase up to an aggregate of $12.5 million of shares of the Company’s common stock over the 30-month term of the Purchase Agreement. Upon execution of the Purchase Agreement, the Company issued and sold 333,333 shares of common stock (the “Initial Shares”) a t a price per share of $1.50, for an aggregate purchase price of $500,000 440,000, which has been recorded as deferred financing costs, with a prorated portion charged to additional paid-in-capital for the Initial Shares, with the remainder of the costs amortized over the term of the Purchase Agreement as there was no guarantee that additional shares would be sold under the Purchase Agreement. Pursuant to the terms of the Purchase Agreement, the Company was able to, from time to time and subject to certain limitations, direct Aspire Capital to purchase shares of the Company’s common stock using pricing formulas based on average prevailing market prices around the time of each sale. Additionally, the Company and Aspire may not effect any sales of shares of the Company's common stock under the Purchase Agreement during the continuance of an event of default or on any trading day that the closing sale price of its common stock is less than $0.40 per share (subject to adjustment for stock dividends, splits, combinations or similar transactions or events). Effective June 19, 2017, the Company terminated the Purchase Agreement, resulting in a write off of the remaining capitalized deferred financing costs relating to the Purchase Agreement of $337,000. From the inception of the Purchase Agreement through June 19, 2017, the Company sold 1,476,991 shares of its common stock under the Purchase Agreement resulting in aggregate gross proceeds to the Company of $2.0 million, in addition to the Initial Shares and the Commitment Shares. On February 8, 2017, the Company entered into a Stock Purchase Agreement (the “SPA”) with PoC Capital, LLC (“PoC”), pursuant to which, among other things, the Company issued to PoC 1,286,173 shares of its common stock. Under the terms of the SPA, PoC has agreed to fund $1.8 million in study costs associated with certain clinical studies, including a planned proof-of-concept trial in patients with Glycogen Storage Disease type Ia (“GSD Ia”). Any study costs in excess of that amount will be the Company’s sole responsibility. The Company has accounted for the $1.8 million as a prepaid expense on the balance sheet. During the three months ended March 31, 2018 and 2017, the Company recorded amortization expense of $225,000 and $42,000, respectively, in clinical study costs related to the SPA with PoC, with a remaining prepaid balance of $581,000 on the balance sheet as of March 31, 2018. On June 14, 2017, the Company entered into a securities purchase agreement (the “Securities Purchase Agreement”), with certain accredited investors (the “Purchasers”), pursuant to which the Company sold an aggregate of 3,749,783 shares (the “Shares”), of its common stock in a registered direct offering (the “Registered Direct Offering”). The Shares were offered by the Company pursuant to the Shelf Registration Statement. In a concurrent private placement, the Company also agreed, pursuant to the Securities Purchase Agreement, to issue and sell to each of the Purchasers a warrant to purchase 0.75 shares of common stock (the “Warrants”), for each share of common stock purchased by a Purchaser in the Registered Direct Offering (the “Private Placement”) and, together with the Registered Direct Offering, (the “Offerings”). The exercise price of the Warrants is $1.30 per share, subject to adjustment as provided therein, and will be exercisable beginning on December 19, 2017 through December 19, 2022. The combined purchase price for one Share and one Warrant to purchase 0.75 shares of common stock in the Offerings was $1.15. The closing of the Offerings occurred on June 19, 2017. The aggregate net proceeds from the Offerings, after deducting the placement agents’ fees and offering expenses, were $3.9 million. On September 28, 2017, the Company entered into a purchase agreement (the “Registered Offering Purchase Agreement”), pursuant to which, on September 29, 2017, the Company sold to Lincoln Park Capital Fund, LLC (“LPC”) 701,282 shares of common stock (the “LPC Initial Shares”), at a price of approximately $1.78 per share for an aggregate purchase price of $1.3 million, pursuant to the Shelf Registration Statement and the prospectus supplement thereto dated September 28, 2017. On September 28, 2017, the Company also entered a purchase agreement (the “Commitment Purchase Agreement”) and a registration rights agreement (the “Registration Rights Agreement”) with LPC, pursuant to which the Company has the right to sell to LPC up to $15.0 million in shares of common stock, subject to certain limitations and conditions set forth in the Commitment Purchase Agreement. Upon the satisfaction of the conditions in the Commitment Purchase Agreement, (the “Commencement”), the Company will have the right, from time to time at its sole discretion over the 30-month period from and after the Commencement, to direct LPC to purchase up to 75,000 shares of common stock on any business day (subject to certain limitations contained in the Commitment Purchase Agreement), with such amounts increasing based on certain threshold prices set forth in the Commitment Purchase Agreement; however, not to exceed $1.0 million in total purchase proceeds per purchase date. The purchase price of shares of common stock that the Company elects to sell to LPC pursuant to the Commitment Purchase Agreement will be based on the market prices of the common stock at the time of such purchases as set forth in the Commitment Purchase Agreement. In addition to regular purchases, as described above, the Company may also direct LPC to purchase additional amounts as accelerated purchases or as additional purchases if the closing sale price of the common stock is not below certain threshold prices, as set forth in the Commitment Purchase Agreement. In all instances, the Company may not sell shares of its common stock to LPC under the Commitment Purchase Agreement if it would result in LPC beneficially owning more than 4.99% of the Common Stock. As consideration for LPC’s commitment to purchase shares of common stock pursuant to the Commitment Purchase Agreement, the Company issued to LPC 100,000 shares of common stock (the “LPC Commitment Shares”) From inception of the Commitment Purchase Agreement through December 31, 2017, Commitment Purchase On December 11, 2017, the Company closed an underwritten public offering of 5,900,000 shares of its common stock, including 769,565 shares sold pursuant to the underwriters’ full exercise of their option to purchase additional shares to cover over-allotments, pursuant to the Shelf Registration Statement at a public offering price of $2.50 per share, for total net proceeds of $13.4 million after deducting underwriting discounts and commissions and other offering expenses. On February 6, 2018, the Company completed an underwritten public offering of common stock pursuant to the Shelf Registration Statement (the “February 2018 Offering”). In the February 2018 Offering, the Company sold 12,650,000 shares of the Company’s common stock at a public offering price of $5.00 per share of common stock. Upon the closing of the February 2018 Offering on February 6, 2018, the Company received net proceeds of $58.7 million, after deducting underwriting discounts, commissions and other offering expenses.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	6. Stock-Based Compensation In connection with the Company’s initial public offering of common stock (the “IPO”), the Company’s 2014 Equity Incentive Plan (the “2014 Plan”) and the Company’s 2014 Employee Stock Purchase Plan (the “ESPP”) became effective on April 28, 2015, the date of the execution and delivery of the underwriting agreement for the IPO. A total of 1,527,770 shares of the Company’s common stock were initially reserved for issuance under the 2014 Plan, and 458,331 shares of the Company’s common stock were initially reserved for issuance under the ESPP. From January 1, 2016 and through March 31, 2018, in accordance with the terms of the 2014 Plan, an additional 2,321,363 shares of the Company’s common stock were added to the number of shares available for issuance under the 2014 Plan, respectively, and, in accordance with the terms of the ESPP, an additional 663,246 shares of the Company’s common stock were added to the number of shares available for issuance under the ESPP, respectively. The Company generally uses the straight-line method to allocate compensation cost to reporting periods over each optionee’s requisite service period, which is generally the vesting period, and estimates the fair value of stock-based awards or restricted stock units to employees and directors using the Black-Scholes option-valuation model. The Black-Scholes model requires the input of subjective assumptions, including volatility, the expected term and the fair value of the underlying common stock on the date of grant, among other inputs. Stock options granted to non-employees are accounted for using the fair value approach. Stock options granted to non-employees are subject to periodic revaluation over their vesting terms. 2014 Plan . The 2014 Plan provides that the compensation committee of the Company’s Board of Directors (the “Compensation Committee”) may grant or issue stock options, stock appreciation rights, restricted shares, restricted stock units and unrestricted shares, deferred share units, performance and cash-settled awards and dividend equivalent rights to participants under the 2014 Plan. Initially, a total of 1,527,770 shares of the Company’s common stock were reserved for issuance pursuant to the 2014 Plan, which number is also the limit on shares of common stock available for awards of incentive stock options. The number of shares available for issuance under the 2014 Plan will, unless otherwise determined by the Company’s Board of Directors or the Compensation Committee, be automatically increased on January 1st of each year commencing on January 1, 2016 and ending on (and including) January 1, 2024, in an amount equal to 3.5% of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year. The shares of common stock deliverable pursuant to awards under the 2014 Plan are authorized but unissued shares of the Company’s common stock, or shares of the Company’s common stock that the Company otherwise holds in treasury or in trust. Any shares of the Company’s common stock underlying awards that are settled in cash or otherwise expire, or are forfeited, terminated or cancelled (including pursuant to an exchange program established by the Compensation Committee) prior to the issuance of stock will again be available for issuance under the 2014 Plan. In addition, shares of the Company’s common stock that are withheld (or not issued) in payment of the exercise price or taxes relating to an award, and shares of the Company’s common stock equal to the number surrendered in payment of any exercise price or withholding taxes relating to an award, will again be available for issuance under the 2014 Plan. ESPP . Initially, a total of 458,331 shares of the Company’s common stock were reserved for issuance pursuant to the ESPP. The number of shares available for issuance under the ESPP will, unless otherwise determined by the Company’s Board of Directors or the Compensation Committee, be automatically increased on January 1st of each year commencing on January 1, 2016 and ending on (and including) January 1, 2024, in an amount equal to 1% of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year. The shares of common stock available for purchase pursuant to the ESPP are authorized but unissued shares of the Company’s common stock, shares of the Company’s common stock that the Company otherwise holds in treasury or shares of the Company’s common stock that were purchased on the open market in arms’ length transactions in accordance with applicable securities laws. Shares of the Company’s common stock will be offered for purchase under the ESPP as determined by the Compensation Committee through a series of successive offerings that each have a term of 24 months and consist of four consecutive purchase periods of six months each. Prior to the commencement of any future offering under the ESPP, the Compensation Committee may determine that the current offering shall end, may commence a new offering on the first day after the end of such terminal purchase period (or any desired later date), and may decide that future offerings will consist of one or more consecutive purchase periods, each to be of such duration as determined by the Compensation Committee; however, no offering will exceed 27 months and no purchase period will exceed one year. Each employee of the Company who (1) is an employee on the first date of any offering under the ESPP, (2) is customarily scheduled to work for more than 20 hours per week and more than five months per calendar year, and (3) meets such other criteria as may be determined by the Compensation Committee (consistent with Section 423 of the Internal Revenue Code of 1986, as amended), is eligible to participate in the ESPP for each purchase period within such offering. The purchase price per share of the Company’s common stock under the ESPP may not be less than, and will initially be equal to, the lesser of: (1) 85% of the fair market value per share of the Company’s common stock on the first day of the offering, or (2) 85% of the fair market value per share of the Company’s common stock on the date the purchase right is exercised, which will be the last day of the applicable purchase period. During the three months ended March 31, 2018 and 2017, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended March 31, 2018 2017 Stock-based compensation expense by type of award: Stock options $ 252 $ 225 Restricted stock and restricted stock units 204 163 Employee stock purchase plan 154 14 Total stock-based compensation expense included in expenses $ 610 $ 402 Stock-based compensation expense by line item: Research and development expenses $ 172 $ 117 General and administrative expenses 438 285 Total stock-based compensation expense included in expenses $ 610 $ 402 The following table sets forth the Company’s unrecognized stock-based compensation expense, net of estimated forfeitures, by type of award and the weighted-average period over which that expense is expected to be recognized (in thousands, except for years): As of March 31, 2018 Unrecognized Expense, Net of Estimated Forfeitures Weighted- average Recognition Period (in years) Type of award: Stock options $ 2,045 2.98 Restricted stock and restricted stock units $ 599 2.16 The following table is a summary of restricted stock activity during the three months ended March 31, 2018: Shares of Restricted Stock Weighted- Average Grant Date Fair Value Unvested at December 31, 2017 245,096 $ 2.53 Granted — $ — Vested — $ — Forfeited — $ — Unvested at March 31, 2018 245,096 $ 2.53 The following table summarizes restricted stock unit activity during the three months ended March 31, 2018: Shares Subject to Restricted Stock Units Weighted- Average Grant Date Value Unvested at December 31, 2017 46,250 $ 5.50 Granted 90,000 $ 4.65 Vested — $ — Forfeited — $ — Unvested March 31, 2018 136,250 $ 4.94 The following table summarizes stock option activity during the three months ended March 31, 2018: Shares Subject to Stock Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Options outstanding at December 31, 2017 1,575,864 $ 2.68 Granted 455,000 $ 4.60 Exercised (44,393 ) $ 1.65 157,000 Cancelled (18,750 ) $ 1.91 Options outstanding at March 31, 2018 1,967,721 $ 3.16 8.66 3,592,000 Options exercisable at March 31, 2018 783,546 $ 3.49 8.07 1,558,000 The Company received $73,000 in cash proceeds from exercises of stock options during the three months ended March 31, 2018. There were no option exercises during the three months ended March 31, 2017. Compensation cost for stock options granted to employees is based on the estimated grant date fair value and is recognized ratably over the vesting period of the applicable option. The estimated per share weighted average fair value of stock options granted to employees during the three months ended March 31, 2018 was $3.26. As stock-based compensation expense recognized is based on options ultimately expected to vest, the fair value of each employee option grant during the three months ended March 31, 2018 was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions: Three Months Ended March 31, 2018 Expected volatility 81.33 % Expected term (in years) 6.10 Risk-free interest rate 2.47 % Expected dividend yield 0 % Expected Volatility. The expected volatility rate used to value stock option grants is based on volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on companies in the pharmaceutical and biotechnology industry in a similar stage of development to the Company. Expected Term . The Company elected to utilize the “simplified” method for “plain vanilla” options to value stock option grants. Under this approach, the weighted-average expected life is presumed to be the average of the vesting term and the contractual term of the option. Risk-free Interest Rate . The risk-free interest rate assumption was based on zero-coupon U.S. Treasury instruments that had terms consistent with the expected term of the Company’s stock option grants. Expected Dividend Yield . The Company has never declared or paid any cash dividends and does not presently plan to pay cash dividends in the foreseeable future. Forfeitures are accounted for as actual forfeitures occur. Since the Company had a net operating loss carryforward as of March 31, 2018, no excess tax benefits for the tax deductions related to stock-based awards were recognized in the Statements of Operations.

Warrants

Warrants	3 Months Ended
	Mar. 31, 2018
Warrants And Rights Note Disclosure [Abstract]
Warrants	7. Warrants Upon the closing of the IPO, on May 4, 2015, the Company issued to the representative of the underwriters as additional compensation a warrant to purchase an aggregate of 82,500 shares of the Company’s common stock. The warrant is exercisable for cash or on a cashless basis at a per share exercise price equal to $10.00 commencing on April 28, 2016, one year following the date of the prospectus filed with the SEC relating to the IPO, and expiring on April 28, 2020. The warrant also provides for registration rights upon request, under certain circumstances. The piggyback registration right provided in connection with the warrant will terminate on April 28, 2022. On April 13, 2016, pursuant to the Offering, the Company sold 7,500,000 shares of its common stock and warrants to purchase up to 7,500,000 shares of its common stock at a public offering price of $1.25 per share of common stock and related warrant. The warrants have an exercise price of $1.50 per share of common stock, were immediately exercisable upon issuance and will expire on April 13, 2021. Additionally, on April 13, 2016, the underwriters for the Offering partially exercised the over-allotment option for warrants to purchase an additional 1,125,000 shares of the Company’s common stock at a public offering price of $0.01 per warrant to purchase a share of common stock. As of March 31, 2018, 6,691,443 warrants were outstanding and 1,481,256 warrants were exercised during the three months ended March 31, 2018. On April 13, 2016, pursuant to the terms of the Loan and Security Agreement , the Company issued to Ligand the Ligand Warrant to purchase up to 960,000 shares of the Company’s common stock. beneficial ownership of the Company’s common stock to greater than 49.9%) The Ligand Warrant was issued to Ligand as a part of the repayment of $1.2 million of the Company’s obligation under the Ligand Note On June 14, 2017, pursuant to the terms of the Securities Purchase Agreement, the Company sold Shares and the Warrants to purchase up to 2,812,337 shares of its common stock to the Purchasers. The combined purchase price for one Share and one Warrant to purchase 0.75 shares of common stock in the Offerings, was $1.15. The closing of the Offerings occurred on June 19, 2017. The Warrants have an exercise price of $1.30 per share, subject to adjustment as provided therein, and will be exercisable beginning on December 19, 2017 through December 19, 2022. Each holder of a Warrant will not have the right to exercise any portion of its Warrant if the holder, together with its affiliates, would beneficially own in excess of 4.99% of the number of shares of common stock outstanding immediately after giving effect to such exercise (the “Beneficial Ownership Limitation”); provided, however, that upon 61 days’ prior notice to the Company, the holder may increase the Beneficial Ownership Limitation; however, in no event shall the Beneficial Ownership Limitation exceed 9.99%. The exercise price and number of shares of common stock issuable upon the exercise of the Warrants will be subject to adjustment in the event of any stock dividends and splits, reverse stock split, recapitalization, reorganization or similar transaction, as described in the Warrants. If a registration statement covering the issuance or resale of the shares of common stock issuable upon exercise of the Warrants is not available for the issuance or resale, as applicable, the Purchasers may exercise the Warrants by means of a “cashless exercise.” On January 16, 2018, the resale registration statement on Form S-1 (File No. 333-222202) that the Company filed related to the 1,987,337 shares subject to unexercised warrants was declared effective by the SEC.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies On July 7, 2015, the Company entered into a Sublease (the “Sublease”) for approximately 7,049 rentable square feet of space located at 12340 El Camino Real, Suite 250, San Diego, California 92130 (the “Premises”). Under the Sublease, the Company is responsible for certain charges for common area maintenance and other costs, and the Sublease provides for abatement of rent during certain periods and escalating rent payments throughout the term of the Sublease. Rent expense is being recorded on a straight line basis over the life of the Sublease and the difference between the rent expense and rent paid is being recorded as deferred rent. Rent expense was $62,000 for each of the three months ended March 31, 2018 and 2017. Future minimum payments pursuant to the Sublease are $107,000 in the aggregate through September 30, 2018, the remaining term of the Sublease.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	9. Subsequent Events The Company has evaluated all subsequent events through the date of filing of this Quarterly Report on Form 10-Q with the SEC, to ensure that this filing includes appropriate disclosure of events both recognized in the financial statements as of March 31, 2018, and events which occurred subsequent to March 31, 2018, but which were not recognized in the financial statements. The Company has determined that there were no subsequent events which required recognition, adjustment to or disclosure in the financial statements.

Organization, Liquidity and M15

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company	The Company Viking Therapeutics, Inc., a Delaware corporation (the “Company”), is a clinical-stage biopharmaceutical company focused on the development of novel therapies for metabolic and endocrine disorders. The Company was incorporated under the laws of the State of Delaware on September 24, 2012 and its principal executive offices are located in San Diego, California.
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying balance sheet as of March 31, 2018, statements of operations for the three months ended March 31, 2018 and 2017 and statements of cash flows for the three months ended March 31, 2018 and 2017 are unaudited. These unaudited financial statements have been prepared in accordance with the rules and regulations of the United States Securities and Exchange Commission (“SEC”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. These financial statements should be read in conjunction with the audited financial statements and the accompanying notes for the year ended December 31, 2017 contained in the Annual Report on Form 10-K filed by the Company with the SEC on March 7, 2018. The unaudited interim financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments (consisting of normal recurring adjustments) necessary to state fairly the Company’s financial position as of March 31, 2018, the results of operations for the three months ended March 31, 2018 and 2017 and cash flows for the three months ended March 31, 2018 and 2017. The December 31, 2017 balance sheet included herein was derived from the audited financial statements, but does not include all disclosures or notes required by GAAP for complete financial statements. The financial data and other information disclosed in these notes to the financial statements related to the three months ended March 31, 2018 and 2017 are unaudited. Interim results are not necessarily indicative of results for an entire year.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying financial statements. Significant estimates made in preparing these financial statements relate to determining the fair value of the debt conversion feature liability and accounting for certain commitments. Actual results could differ from those estimates.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Adopted Accounting Standards In May 2014, the FASB issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. The FASB has subsequently issued the following amendments to ASU No. 2014-09, which have the same effective date and transition date of January 1, 2018: • In August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers • In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers • In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers • In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers • In December 2016, the FASB issued ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, which amends certain narrow aspects of the guidance issued in ASU No. 2014-09 including guidance related to the disclosure of remaining performance obligations and prior-period performance obligations, as well as other amendments to the guidance on loan guarantee fees, contract costs, refund liabilities, advertising costs and the clarification of certain examples. The Company evaluated the potential impact that these standards had on its financial position and results of operations. There is no current impact of this new guidance on its financial statements as the Company does not currently have any revenue generating arrangements. In August 2016, the FASB issued ASU No. 2016-15, Classification of Certain Cash Receipts and Cash Payments The Company’s adoption of ASU 2016-15 on January 1, 2018 did not have a material effect on its financial statements and related disclosures. Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases for the Company in the first quarter of fiscal year 2019 and early adoption is permitted. ASU 2016-02 is required to be applied with a modified retrospective approach and requires application of the new standard at the beginning of the earliest comparative period presented. The Company does not expect the adoption of ASU 2016-02 to have a material effect on its financial statements and related disclosures. In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments The Company is evaluating the effect that ASU 2016-13 will have on its financial statements and related disclosures. In July 2017, the FASB issued a two-part ASU No. 2017-11 , I. Accounting for Certain Financial Instruments with Down Round Features and II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with maturities of three months or less from the date of purchase to be cash equivalents.
Investments Available-for-Sale	Investments Available-for-Sale Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive income (loss). The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. The amortization of premiums and accretion of discounts is included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments, which potentially subject the Company to concentration of credit risk, consist primarily of cash and cash equivalents and marketable securities. The Company maintains deposits in federally insured depository institutions in excess of federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. Additionally, the Company has established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity.
Prepaid Clinical Trial and Preclinical Study Costs	Prepaid Clinical Trial and Preclinical Study Costs Prepaid clinical trial and preclinical study costs represent advance payments by the Company for future clinical trial and preclinical study services to be performed by the clinical research organization and other research organizations. Such amounts are recognized as research and development expense as the related clinical trial and preclinical study services are performed.
Deferred Financing Costs	Deferred Financing Costs Deferred financing costs represent legal, accounting and other direct costs related to the Company’s efforts to raise capital through a public or private sale of the Company’s common stock. Costs related to public sales of the Company’s common stock are deferred until the completion of the applicable offering, at which time such costs are reclassified to additional paid-in-capital as a reduction of the proceeds. Costs related to private sales of the Company’s common stock are deferred until the completion of the applicable offering, at which time such costs are amortized over the term of the applicable purchase agreement.
Revenue Recognition	Revenue Recognition The Company has not recorded any revenues since its inception. However, in the future, the Company may enter into collaborative research and licensing agreements, under which the Company could be eligible for payments made in the form of upfront license fees, research funding, cost reimbursement, contingent event-based payments and/or royalties. On January 1, 2018, the Company adopted ASU 2014-09, Revenue from Contracts with Customers and all related amendments ("ASC 606" or "the new revenue standard"). ASC 606 is a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-s
Research and Development Expenses	Research and Development Expenses All costs of research and development are expensed in the period incurred. Research and development costs primarily consist of fees paid to contract research organizations (“CROs”) and clinical trial sites, employee and consultant related expenses, which include salaries, benefits and stock-based compensation for research and development personnel, external research and development expenses incurred pursuant to agreements with third-party manufacturing organizations, facilities costs, travel costs, dues and subscriptions, depreciation and materials used in preclinical studies, clinical trials and research and development. The Company estimates its preclinical study and clinical trial expenses based on the services it received pursuant to contracts with research institutions and CROs that conduct and manage preclinical studies and clinical trials on the Company’s behalf. Clinical trial-related contracts vary significantly in length, and may be for a fixed amount, based on milestones or deliverables, a variable amount based on actual costs incurred, capped at a certain limit, or for a combination of these elements. The Company accrues service fees based on work performed, which relies on estimates of total costs incurred based on milestones achieved, patient enrollment and other events. The majority of the Company’s service providers invoice the Company in arrears, and to the extent that amounts invoiced differ from its estimates of expenses incurred, the Company accrues for additional costs. The financial terms of these agreements vary from contract to contract and may result in uneven expenses and payment flows. Preclinical study and clinical trial expenses include: • fees paid to CROs, consultants and laboratories in connection with preclinical studies; • fees paid to CROs, clinical trial sites, investigators and consultants in connection with clinical trials; and • fees paid to contract manufacturers and service providers in connection with the production, testing and packaging of active pharmaceutical ingredients and drug materials for preclinical studies and clinical trials. Payments under some of these agreements depend on factors such as the milestones accomplished, including enrollment of certain numbers of patients, site initiation and the completion of clinical trial milestones. To date, the Company has not experienced any events requiring it to make material adjustments to its accruals for service fees. If the Company does not identify costs that it has begun to incur or if it underestimates or overestimates the level of services performed or the costs of these services, its actual expenses could differ from its estimates which could materially affect its results of operations. Adjustments to the Company’s accruals are recorded as changes in estimates become evident. Furthermore, based on amounts invoiced to the Company by its service providers, the Company may also record payments made to those providers as prepaid expenses that will be recognized as expense in future periods as services are rendered. In May 2014, the Company entered into the Master License Agreement, pursuant to which it acquired certain rights to a number of research and development programs from Ligand Pharmaceuticals Incorporated, or Research and Development,
Patent Costs	Patent Costs Costs related to filing and pursuing patent applications are expensed as incurred to general and administrative expense, as recoverability of such expenditures is uncertain.
Stock-Based Compensation	Stock-Based Compensation The Company generally uses the straight-line method to allocate compensation cost to reporting periods over each optionee’s requisite service period, which is generally the vesting period, and estimates the fair value of stock-based awards or restricted stock units to employees and directors using the Black-Scholes option-valuation model. The Black-Scholes model requires the input of subjective assumptions, including volatility, the expected term and the fair value of the underlying common stock on the date of grant, among other inputs. For restricted stock and restricted stock unit awards, the Company generally uses the straight-line method to allocate compensation cost to reporting periods over the holder’s requisite service period, which is generally the vesting period, and uses the fair value at grant date to value the awards. For restricted stock that vests upon the satisfaction of certain performance conditions, the Company recognizes stock-based compensation expense when it becomes probable that the performance conditions will be met. At the point that it becomes probable that the performance conditions will be met, the Company records a cumulative catch-up of the expense from the grant date to the current date, and the Company then amortizes the remainder of the expense over the remaining service period.
Income Taxes	Income Taxes The Company accounts for its income taxes using the liability method whereby deferred tax assets and liabilities are determined based on temporary differences between the basis used for financial reporting and income tax reporting purposes. Deferred income taxes are provided based on the enacted tax rates in effect at the time such temporary differences are expected to reverse. A valuation allowance is provided for deferred tax assets if it is more likely than not that the Company will not realize those tax assets through future operations. ASC Topic 740-10, Income Taxes The Company’s policy is to recognize interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense.
Net Loss per Common Share	Net Loss per Common Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. The following table presents the computation of basic and diluted net loss per common share (in thousands, except per share data): Three Months Ended March 31, 2018 2017 Net Loss Net loss attributable to common stockholders - Basic $ (3,551 ) $ (5,222 ) Change in fair value of debt conversion feature liability (1,361 ) — Amortization of debt discount 258 — Interest expense 24 — Net loss attributable to common stockholders - Diluted $ (4,630 ) $ (5,222 ) Basic Shares Weighted-average common shares outstanding 44,893,895 22,660,017 Less: Weighted-average shares subject to repurchase (245,096 ) (307,096 ) Denominator for basic net loss per share 44,648,799 22,352,921 Diluted Shares Weighted-average common shares outstanding 44,893,895 22,660,017 Weighted-average shares subject to repurchase (245,096 ) (307,096 ) Effect of dilutive shares issuable upon conversion of debt 656,716 — Denominator for diluted net loss per share 45,305,515 22,352,921 Net loss per share: Basic $ (0.08 ) $ (0.23 ) Diluted $ (0.10 ) $ (0.23 ) Potentially dilutive securities that are not included in the calculation of diluted net loss per share because their effect is anti-dilutive are as follows (in common equivalent shares): As of March 31, 2018 2017 Common stock warrants 8,780,838 9,667,500 Restricted stock units 136,250 69,375 Common stock subject to repurchase 245,096 307,096 Common stock options 1,967,721 1,511,894 Shares issuable upon conversion of debt — 2,860,361 11,129,905 14,416,226
Segments	Segments The Company operates in only one segment. Management uses cash flows as the primary measure to manage its business and does not segment its business for internal reporting or decision making purposes.

Organization, Liquidity and M16

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Computation of Basic and Diluted Net Loss per Common Share	The following table presents the computation of basic and diluted net loss per common share (in thousands, except per share data): Three Months Ended March 31, 2018 2017 Net Loss Net loss attributable to common stockholders - Basic $ (3,551 ) $ (5,222 ) Change in fair value of debt conversion feature liability (1,361 ) — Amortization of debt discount 258 — Interest expense 24 — Net loss attributable to common stockholders - Diluted $ (4,630 ) $ (5,222 ) Basic Shares Weighted-average common shares outstanding 44,893,895 22,660,017 Less: Weighted-average shares subject to repurchase (245,096 ) (307,096 ) Denominator for basic net loss per share 44,648,799 22,352,921 Diluted Shares Weighted-average common shares outstanding 44,893,895 22,660,017 Weighted-average shares subject to repurchase (245,096 ) (307,096 ) Effect of dilutive shares issuable upon conversion of debt 656,716 — Denominator for diluted net loss per share 45,305,515 22,352,921 Net loss per share: Basic $ (0.08 ) $ (0.23 ) Diluted $ (0.10 ) $ (0.23 )
Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share	Potentially dilutive securities that are not included in the calculation of diluted net loss per share because their effect is anti-dilutive are as follows (in common equivalent shares): As of March 31, 2018 2017 Common stock warrants 8,780,838 9,667,500 Restricted stock units 136,250 69,375 Common stock subject to repurchase 245,096 307,096 Common stock options 1,967,721 1,511,894 Shares issuable upon conversion of debt — 2,860,361 11,129,905 14,416,226

Investments in Marketable Sec17

Investments in Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2018
Investments Debt And Equity Securities [Abstract]
Summary of Investments Classified As Available-For-Sale Securities	Investments classified as available-for-sale as of March 31, 2018 consisted of the following (in thousands): As of March 31, 2018 Amortized Cost Gross Unrealized Gains ( 1) Gross Unrealized Losses ( 1) Aggregate Estimated Fair Value Certificates of deposit ( 2) $ 250 $ — $ — $ 250 Corporate debt securities ( 2) 40,963 — (101 ) 40,862 $ 41,213 $ — $ (101 ) $ 41,112 (1) Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At March 31, 2018, there were no securities in an unrealized gain position and there were 56 securities in an unrealized loss position. These unrealized losses were less than $5,000 individually and $101,000 in the aggregate. These securities have not been in a continuous unrealized gain or loss position for more than 12 months. The Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis, which may be at maturity. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value. (2) At March 31, 2018, none of these securities were classified as cash and cash equivalents on the Company’s balance sheet and none of these securities were scheduled to mature outside of one year. Investments classified as available-for-sale as of December 31, 2017 consisted of the following (in thousands): As of December 31, 2017 Amortized Cost Gross Unrealized Gains ( 1) Gross Unrealized Losses ( 1) Aggregate Estimated Fair Value Certificates of deposit ( 2) $ 249 $ — $ — $ 249 Corporate debt securities ( 2) 11,357 — (19 ) 11,338 $ 11,606 $ — $ (19 ) $ 11,587 (1) Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At December 31, 2017, there were 29 securities in an unrealized loss position. These unrealized losses were less than $3,000 individually and $19,000 in the aggregate. These securities have not been in a continuous unrealized loss position for more than 12 months. The Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis, which may be at maturity. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value. ( 2 ) At December 31, 2017, none of these securities were classified as cash and cash equivalents on the Company’s balance sheet and none of these securities were scheduled to mature outside of one year.

Fair Value of Financial Instr18

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Summary of Fair Values of Financial Instruments	The fair values of the Company’s financial instruments are presented below (in thousands): Fair Value Measurements at March 31, 2018 Total Level 1 Level 2 Level 3 Financial assets carried at fair value: Cash equivalents: Government money market funds $ 21,876 $ 21,876 $ — $ — Corporate debt securities, available-for-sale 15,777 — 15,777 — Short-term investments Certificates of deposit, available-for-sale 250 — 250 — Corporate debt securities, available-for-sale 40,862 — 40,862 — Total financial assets $ 78,765 $ 21,876 $ 56,889 $ — Financial liabilities carried at fair value: Debt conversion feature - current $ 37 $ — $ — $ 37 Total financial liabilities $ 37 $ — $ — $ 37 Fair Value Measurements at December 31, 2017 Total Level 1 Level 2 Level 3 Financial assets carried at fair value: Cash equivalents: Government money market funds $ 6,361 $ 6,361 $ — $ — Corporate debt securities, available-for-sale 1,244 — 1,244 — Short-term investments Certificates of deposit, available-for-sale 249 — 249 — Corporate debt securities, available-for-sale 11,338 — 11,338 — Total financial assets $ 19,192 $ 6,361 $ 12,831 $ — Financial liabilities carried at fair value: Debt conversion feature - current $ 1,398 $ — $ — $ 1,398 Total financial liabilities $ 1,398 $ — $ — $ 1,398
Summary of Changes in Debt Conversion Feature Liability Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs	The table below presents a summary of changes in the Company’s debt conversion feature liability measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the three months ended March 31, 2018 and 2017 (in thousands): Three Months Ended March 31, 2018 2017 Debt conversion feature: Beginning balance $ 1,398 $ 731 Adjustments resulting from changes in fair value recognized in earnings (1,361 ) (278 ) Ending balance $ 37 $ 453
Schedule of Valuation Techniques and Significant Unobservable Inputs Used to Determine Fair Value of Significant Level 3 Liabilities	The following table sets forth the Company’s valuation techniques and significant unobservable inputs used to determine fair value for significant Level 3 liabilities (in thousands, except for volatility and risk free rate): Fair Value Significant Assets Liabilities Valuation Technique(s) Unobservable Input % Debt conversion feature liability March 31, 2018 $ — $ 37 Black-Scholes-Merton option valuation model Volatility 63% Risk Free Rate 1.68% December 31, 2017 $ — $ 1,398 Black-Scholes-Merton option valuation model Volatility 100% Risk Free Rate 1.46%

Convertible Notes Payable (Tabl

Convertible Notes Payable (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Schedule of Convertible Notes Payable	Convertible notes payable consisted of the following (in thousands): March 31, December 31, 2018 2017 Current maturities: Convertible note payable issued during 2014 to Ligand pursuant to the Master License Agreement with a 5% annual interest rate, due during 2016 (amended in January 2016 to a 2.5% annual interest rate with maturity extended to 2017, and subsequently amended in May 2017 with maturity extended to May 21, 2018) $ 1,917 $ 1,917 Conversion payoff value 1,950 1,938 Discount on notes payable, current (146 ) (404 ) Convertible notes payable, current (net of discount) $ 3,721 $ 3,451

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
Summary of Stock-based Compensation Expense Recognized	During the three months ended March 31, 2018 and 2017, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended March 31, 2018 2017 Stock-based compensation expense by type of award: Stock options $ 252 $ 225 Restricted stock and restricted stock units 204 163 Employee stock purchase plan 154 14 Total stock-based compensation expense included in expenses $ 610 $ 402 Stock-based compensation expense by line item: Research and development expenses $ 172 $ 117 General and administrative expenses 438 285 Total stock-based compensation expense included in expenses $ 610 $ 402
Schedule of Unrecognized Stock-based Compensation Expense, Net of Estimated Forfeitures, by Type of Award and Weighted-average Recognition Period	The following table sets forth the Company’s unrecognized stock-based compensation expense, net of estimated forfeitures, by type of award and the weighted-average period over which that expense is expected to be recognized (in thousands, except for years): As of March 31, 2018 Unrecognized Expense, Net of Estimated Forfeitures Weighted- average Recognition Period (in years) Type of award: Stock options $ 2,045 2.98 Restricted stock and restricted stock units $ 599 2.16
Summary of Stock Option Activity	The following table summarizes stock option activity during the three months ended March 31, 2018: Shares Subject to Stock Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Options outstanding at December 31, 2017 1,575,864 $ 2.68 Granted 455,000 $ 4.60 Exercised (44,393 ) $ 1.65 157,000 Cancelled (18,750 ) $ 1.91 Options outstanding at March 31, 2018 1,967,721 $ 3.16 8.66 3,592,000 Options exercisable at March 31, 2018 783,546 $ 3.49 8.07 1,558,000
Schedule of Weighted Average Assumptions using Black-Scholes Option Pricing Model	the fair value of each employee option grant during the three months ended March 31, 2018 was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions: Three Months Ended March 31, 2018 Expected volatility 81.33 % Expected term (in years) 6.10 Risk-free interest rate 2.47 % Expected dividend yield 0 %
Restricted stock [Member]
Summary of Stock Activity	The following table is a summary of restricted stock activity during the three months ended March 31, 2018: Shares of Restricted Stock Weighted- Average Grant Date Fair Value Unvested at December 31, 2017 245,096 $ 2.53 Granted — $ — Vested — $ — Forfeited — $ — Unvested at March 31, 2018 245,096 $ 2.53
Restricted stock units [Member]
Summary of Stock Activity	The following table summarizes restricted stock unit activity during the three months ended March 31, 2018: Shares Subject to Restricted Stock Units Weighted- Average Grant Date Value Unvested at December 31, 2017 46,250 $ 5.50 Granted 90,000 $ 4.65 Vested — $ — Forfeited — $ — Unvested March 31, 2018 136,250 $ 4.94

Organization, Liquidity and M21

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018Segment
Accounting Policies [Abstract]
Date of incorporation	Sep. 24, 2012
State of Incorporation	Delaware
Highly liquid investments maturities	Three months or less
Number of operating segment	1

Organization, Liquidity and M22

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies - Schedule of Computation of Basic and Diluted Net Loss per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net Loss
Net loss attributable to common stockholders - Basic	$ (3,551)	$ (5,222)
Change in fair value of debt conversion feature liability	(1,361)	(278)
Amortization of debt discount	258	431
Interest expense	24
Net loss attributable to common stockholders - Diluted	$ (4,630)	$ (5,222)
Basic Shares
Weighted-average common shares outstanding	44,893,895	22,660,017
Less: Weighted-average shares subject to repurchase	(245,096)	(307,096)
Denominator for basic net loss per share	44,648,799	22,352,921
Diluted Shares
Weighted-average common shares outstanding	44,893,895	22,660,017
Less: Weighted-average shares subject to repurchase	(245,096)	(307,096)
Effect of dilutive shares issuable upon conversion of debt	656,716
Denominator for diluted net loss per share	45,305,515	22,352,921
Net loss per common share
Basic	$ (0.08)	$ (0.23)
Diluted	$ (0.10)	$ (0.23)

Organization, Liquidity and M23

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded in calculation of diluted net loss per share	11,129,905	14,416,226
Common stock warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded in calculation of diluted net loss per share	8,780,838	9,667,500
Restricted stock units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded in calculation of diluted net loss per share	136,250	69,375
Common stock subject to repurchase [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded in calculation of diluted net loss per share	245,096	307,096
Stock options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded in calculation of diluted net loss per share	1,967,721	1,511,894
Shares issuable upon conversion of debt [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded in calculation of diluted net loss per share		2,860,361

Investments in Marketable Sec24

Investments in Marketable Securities - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Available For Sale Securities [Abstract]
Proceeds from sales of available-for-sale securities	$ 0	$ 0

Investments in Marketable Sec25

Investments in Marketable Securities - Summary of Investments Classified As Available-For-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 41,213	$ 11,606
Gross Unrealized Losses	(101)	(19)
Aggregate Estimated Fair Value	41,112	11,587
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	250	249
Aggregate Estimated Fair Value	250	249
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,963	11,357
Gross Unrealized Losses	(101)	(19)
Aggregate Estimated Fair Value	$ 40,862	$ 11,338

Investments in Marketable Sec26

Investments in Marketable Securities - Summary of Investments Classified As Available-For-Sale Securities (Parenthetical) (Detail)	Mar. 31, 2018USD ($)Security	Dec. 31, 2017USD ($)Security
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized gain position | Security	0
Number of securities in unrealized loss position | Security	56	29
Unrealized losses, aggregate	$ 101,000	$ 19,000
Short-term investments – available for sale	41,112,000	11,587,000
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments – available for sale	250,000	249,000
Short-term investments classified as available-for-sale, noncurrent	0	0
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, aggregate	101,000	19,000
Short-term investments – available for sale	40,862,000	11,338,000
Short-term investments classified as available-for-sale, noncurrent	0	0
Cash equivalents [Member] | Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments – available for sale	0	0
Cash equivalents [Member] | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments – available for sale	0	0
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, individually	5,000	3,000
Unrealized losses, aggregate	$ 101,000	$ 19,000

Fair Value of Financial Instr27

Fair Value of Financial Instruments - Summary of Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial assets carried at fair value:
Short-term investments – available for sale	$ 41,112	$ 11,587
Total financial assets	78,765	19,192
Financial liabilities carried at fair value:
Debt conversion feature - current	37	1,398
Total financial liabilities	37	1,398
Level 1 [Member]
Financial assets carried at fair value:
Total financial assets	21,876	6,361
Level 2 [Member]
Financial assets carried at fair value:
Total financial assets	56,889	12,831
Level 3 [Member]
Financial liabilities carried at fair value:
Debt conversion feature - current	37	1,398
Total financial liabilities	37	1,398
Government money market funds [Member]
Financial assets carried at fair value:
Cash and cash equivalents, fair value disclosure	21,876	6,361
Government money market funds [Member] | Level 1 [Member]
Financial assets carried at fair value:
Cash and cash equivalents, fair value disclosure	21,876	6,361
Corporate debt securities, available-for-sale [Member]
Financial assets carried at fair value:
Cash and cash equivalents, fair value disclosure	15,777	1,244
Short-term investments – available for sale	40,862	11,338
Corporate debt securities, available-for-sale [Member] | Level 2 [Member]
Financial assets carried at fair value:
Cash and cash equivalents, fair value disclosure	15,777	1,244
Short-term investments – available for sale	40,862	11,338
Certificates of deposit, available-for-sale [Member]
Financial assets carried at fair value:
Short-term investments – available for sale	250	249
Certificates of deposit, available-for-sale [Member] | Level 2 [Member]
Financial assets carried at fair value:
Short-term investments – available for sale	$ 250	$ 249

Fair Value of Financial Instr28

Fair Value of Financial Instruments - Summary of Changes in Debt Conversion Feature Liability Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) - Debt Conversion Feature Liability [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 1,398	$ 731
Adjustments resulting from changes in fair value recognized in earnings	(1,361)	(278)
Ending balance	$ 37	$ 453

Fair Value of Financial Instr29

Fair Value of Financial Instruments - Schedule of Valuation Techniques and Significant Unobservable Inputs Used to Determine Fair Value of Significant Level 3 Liabilities (Detail) - Debt Conversion Feature Liability [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Liabilities	$ 37	$ 1,398	$ 453	$ 731
Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Assets	0	0
Fair Value, Liabilities	$ 37	$ 1,398
Valuation Technique(s)	Black-Scholes-Merton option valuation model	Black-Scholes-Merton option valuation model
Level 3 [Member] | Black-Scholes-Merton Option Valuation Model [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions, Volatility	63.00%	100.00%
Fair Value Assumptions, Risk Free Rate	1.68%	1.46%

Convertible Notes Payable - Sch

Convertible Notes Payable - Schedule of Convertible Notes Payable (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Conversion payoff value	$ 1,950	$ 1,938
Discount on notes payable, current	(146)	(404)
Convertible notes payable, current (net of discount)	3,721	3,451
Ligand Note [Member] | Short Term Debt [Member]
Debt Instrument [Line Items]
Convertible note payable issued during 2014 to Ligand pursuant to the Master License Agreement with a 5% annual interest rate, due during 2016 (amended in January 2016 to a 2.5% annual interest rate with maturity extended to 2017, and subsequently amended in May 2017 with maturity extended to May 21, 2018)	$ 1,917	$ 1,917

Convertible Notes Payable - S31

Convertible Notes Payable - Schedule of Convertible Notes Payable (Parenthetical) (Detail)	May 08, 2017	Jan. 22, 2016	Dec. 31, 2016
Debt Disclosure [Abstract]
Interest rate for current maturities		2.50%	5.00%
Due date for current maturities		2,017	2,016
Debt instrument current maturity date	May 21, 2018

Convertible Notes Payable - Add

Convertible Notes Payable - Additional Information (Detail) - USD ($)	Dec. 11, 2017	May 08, 2017	Apr. 13, 2016	Jan. 22, 2016	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Jan. 21, 2016	May 21, 2014
Debt Instrument [Line Items]
Date of registration rights agreement amendment					Jan. 22, 2016
Proceeds from issuances of common stock, net of underwriting discounts and commissions			$ 7,800,000		$ 58,822,000		$ 2,540,000
Underwriting discounts, commissions and other offering expenses			$ 1,600,000
Common stock sold	5,900,000		7,500,000
Warrants sold			7,500,000
Warrants exercise price per share of common stock			$ 1.50		$ 10
Warrants expiry date					Apr. 13, 2021
Change in fair value of debt conversion feature liability					$ 1,361,000		278,000
Interest expense					24,000
Amortization of debt discount					258,000		431,000
Ligand Note [Member]
Debt Instrument [Line Items]
Note obligation					1,500,000
Required payment in cash for note obligation					300,000
Repayments of notes payable in stock					1,200,000
Change in fair value of debt conversion feature liability					1.4		278,000
Interest expense					24,000		24,000
Amortization of debt discount					$ 258,000		$ 431,000
Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Aggregate net proceeds from issue of equity securities				$ 2,000,000
Shares issued price per share				$ 8
Debt Instrument repayment, description					Each $1.00 of the $1.5 million payment reduced the amount of accrued and unpaid interest and then unpaid principal amount of the loans under the Ligand Note by $0.50.
Additional repayment notice period within closing of the next financing					180 days
Additional repayment notice period after the closing of the next financing					180 days
Weighted average closing price of common stock period					30 days
Loan and Security Agreement [Member] | Ligand [Member]
Debt Instrument [Line Items]
Repayments of notes payable in stock			$ 1,200,000
Common stock sold			960,000
Warrants sold			960,000
Warrants exercise price per share of common stock			$ 1.50
Warrants expiry date					Apr. 13, 2021
Loan and Security Agreement [Member] | Minimum [Member]
Debt Instrument [Line Items]
Beneficial ownership of company's common stock		49.90%	49.90%
Loan and Security Agreement [Member] | Ligand Note [Member]
Debt Instrument [Line Items]
Loan and security agreement, maturity date				May 21, 2017
Note obligation				$ 1,500,000
Loan and Security Agreement [Member] | Ligand Note [Member] | Minimum [Member]
Debt Instrument [Line Items]
Required payment in cash for note obligation				$ 300,000
Debt Conversion Feature Liability [Member] | Ligand Note [Member]
Debt Instrument [Line Items]
Adjustments resulting from modification of debt					$ 576,000
Third Amendment to Loan and Security Agreement [Member] | Ligand Note [Member]
Debt Instrument [Line Items]
Loan and security agreement, maturity date		May 21, 2018
Required payment in cash for note obligation						$ 200,000
Debt Instrument repayment, description					Each $1.00 of value of the Required Repayment reduced the amount of accrued and unpaid interest and then unpaid principal amount on the Loans by $0.50.
Change in fair value of debt conversion feature liability		$ 1,000,000
Ligand Debt
Debt Instrument [Line Items]
Loan and security agreement									$ 2,500,000
Fixed accrued interest rate				2.50%				5.00%
Fixed accrued interest rate of default loan					8.00%
Loan and security agreement, maturity date					May 21, 2018
Note conversion, principal amount of loan plus all accrued and previously unpaid interest					200.00%

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail)

Feb. 06, 2018USD ($)$ / sharesshares

Dec. 11, 2017USD ($)$ / sharesshares

Sep. 29, 2017USD ($)$ / sharesshares

Sep. 28, 2017USD ($)shares

Jun. 19, 2017USD ($)$ / shares

Jun. 14, 2017USD ($)$ / sharesshares

Feb. 08, 2017USD ($)shares

Aug. 24, 2016USD ($)$ / sharesshares

Jun. 20, 2016shares

Apr. 13, 2016USD ($)$ / sharesshares

May 31, 2015USD ($)$ / sharesshares

Feb. 28, 2014Tranche$ / sharesshares

Mar. 31, 2018USD ($)$ / sharesshares

Mar. 31, 2017USD ($)

Jun. 19, 2017USD ($)$ / sharesshares

Jul. 26, 2017USD ($)shares

Dec. 31, 2016USD ($)

Dec. 31, 2017$ / sharesshares

Feb. 20, 2014USD ($)

Equity [Line Items]

Preferred stock, shares authorized

10,000,000

10,000,000

Preferred stock, par value | $ / shares

$ 0.00001

$ 0.00001

Preferred stock, shares outstanding

0

0

Common stock, shares authorized

300,000,000

300,000,000

Common stock, par value | $ / shares

$ 0.00001

$ 0.00001

Number of common stock for issuance in exchange for future services from founders

1,000,000

Common stock price per share | $ / shares

$ 0.01

Number of tranches | Tranche

2

Unrecognized compensation expense | $

$ 62,000

$ 168,000

Common stock shares repurchased

633,810

Repurchase of common stock from stockholders, per share | $ / shares

$ 0.00001

Remaining number of repurchased shares

366,190

Common stock sold

5,900,000

7,500,000

Cash proceeds from common stock issuance | $

$ 7,800,000

$ 58,822,000

$ 2,540,000

Shares issued to cover future clinical study costs | $

1,800,000

Common stock, price per share | $ / shares

$ 1.25

Warrants exercise price per share of common stock | $ / shares

$ 1.50

$ 10

Warrants expiry date

Apr. 13, 2021

Over-Allotment Option [Member]

Equity [Line Items]

Common stock sold

769,565

Cash proceeds from common stock issuance | $

$ 13,400,000

Common stock, price per share | $ / shares

$ 2.50

Securities Purchase Agreement [Member]

Equity [Line Items]

Public offering price per share and per warrant | $ / shares

$ 1.15

$ 1.15

$ 1.15

Securities Purchase Agreement [Member] | Private Placement and Registered Direct Offering [Member]

Equity [Line Items]

Cash proceeds from common stock issuance | $

$ 3,900,000

Number of warrants issued for common stock

0.75

Warrants exercise price per share of common stock | $ / shares

$ 1.30

Warrants exercisable date

Dec. 19, 2017

Dec. 19, 2017

Warrants expiry date

Dec. 19, 2022

Dec. 19, 2022

Common Stock [Member] | February 2018 Offering [Member]

Equity [Line Items]

Common stock sold

12,650,000

Cash proceeds from common stock issuance | $

$ 58,700,000

Common stock, price per share | $ / shares

$ 5

Common Stock [Member] | Securities Purchase Agreement [Member] | Private Placement and Registered Direct Offering [Member]

Equity [Line Items]

Common stock sold

3,749,783

Maxim [Member]

Equity [Line Items]

Registration statement commencement date

Jul. 26, 2016

Equity distribution agreement termination date

Jul. 26, 2017

Cash proceeds from common stock issuance | $

$ 1,600,000

Maxim [Member] | Common Stock [Member]

Equity [Line Items]

Common stock sold

1,267,237

Maxim [Member] | Common Stock [Member] | Maximum [Member]

Equity [Line Items]

Sale of common stock, shares

3,748,726

Aspire Capital [Member] | Common Stock Purchase Agreement [Member]

Equity [Line Items]

Write off of remaining capitalized deferred financing costs | $

$ 337,000

Aspire Capital [Member] | Common Stock [Member] | Common Stock Purchase Agreement [Member]

Equity [Line Items]

Common stock sold

333,333

1,476,991

Cash proceeds from common stock issuance | $

$ 2,000,000

Common stock sold aggregate purchase price | $

$ 500,000

Common stock purchase agreement term

30 months

Minimum closing sale price per share to execute transactions under agreement | $ / shares

$ 0.40

Common stock issued as consideration for commitment fee

336,116

Shares issued to cover future clinical study costs | $

$ 440,000

Common stock, price per share | $ / shares

$ 1.50

Aspire Capital [Member] | Common Stock [Member] | Maximum [Member] | Common Stock Purchase Agreement [Member]

Equity [Line Items]

Common stock sold aggregate purchase price | $

$ 12,500,000

PoC Capital, LLC [Member]

Equity [Line Items]

Amortization expense | $

$ 225,000

42,000

Prepaid clinical study costs | $

$ 1,800,000

$ 581,000

PoC Capital, LLC [Member] | Common Stock [Member] | Stock Purchase Agreement [Member]

Equity [Line Items]

Common stock sold

1,286,173

PoC Capital, LLC [Member] | Common Stock [Member] | Stock Purchase Agreement [Member] | Clinical Studies [Member]

Equity [Line Items]

Common stock sold aggregate purchase price | $

$ 1,800,000

LPC [Member] | Common Stock [Member] | Registered Offering Purchase Agreement [Member]

Equity [Line Items]

Common stock sold

701,282

Common stock sold aggregate purchase price | $

$ 1,300,000

Common stock, price per share | $ / shares

$ 1.78

LPC [Member] | Common Stock [Member] | Commitment Purchase Agreement [Member] | Registration Rights Agreement [Member]

Equity [Line Items]

Common stock sold

343,051

0

Common stock purchase agreement term

30 months

Common stock issued as consideration for commitment

100,000

Gross proceeds from common stock issuance | $

$ 802,000

LPC [Member] | Common Stock [Member] | Maximum [Member] | Commitment Purchase Agreement [Member] | Registration Rights Agreement [Member]

Equity [Line Items]

Total of purchase agreement and potential aggregate future purchases | $

$ 15,000,000

Common stock to be sold, subject to certain limitations

75,000

Total purchase proceeds per purchase date, subject to certain limitations | $

$ 1,000,000

LPC [Member] | Common Stock [Member] | Minimum [Member] | Commitment Purchase Agreement [Member] | Registration Rights Agreement [Member]

Equity [Line Items]

Percentage of shares may not sell if it is beneficial owning

4.99%

Tranche One [Member]

Equity [Line Items]

Number of common stock for issuance in exchange for future services from founders

500,000

Remaining number of repurchased shares

183,095

Stock compensation expense | $

$ 0

$ 0

$ 31,000

Tranche Two [Member]

Equity [Line Items]

Number of common stock for issuance in exchange for future services from founders

500,000

Remaining number of repurchased shares

183,095

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018USD ($)Period$ / sharesshares	Mar. 31, 2017shares	Apr. 28, 2015shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash proceeds from exercises of stock options | $	$ 73,000
Option exercises	44,393	0
Weighted average fair value of stock options granted to employees | $ / shares	$ 3.26
Excess tax benefit from stock-based awards | $	$ 0
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock reserved for issuance			1,527,770
Additional number of shares of common stock reserved for issuance	2,321,363
Common stock reserved for issuance, description	Initially, a total of 1,527,770 shares of the Company’s common stock were reserved for issuance pursuant to the 2014 Plan, which number is also the limit on shares of common stock available for awards of incentive stock options. The number of shares available for issuance under the 2014 Plan will, unless otherwise determined by the Company’s Board of Directors or the Compensation Committee, be automatically increased on January 1st of each year commencing on January 1, 2016 and ending on (and including) January 1, 2024, in an amount equal to 3.5% of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year.
Percentage of common stock outstanding to increase shares reserved for issuance	3.50%
2014 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock reserved for issuance			458,331
Additional number of shares of common stock reserved for issuance	663,246
Common stock reserved for issuance, description	The number of shares available for issuance under the ESPP will, unless otherwise determined by the Company’s Board of Directors or the Compensation Committee, be automatically increased on January 1st of each year commencing on January 1, 2016 and ending on (and including) January 1, 2024, in an amount equal to 1% of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year.
Percentage of common stock outstanding to increase shares reserved for issuance	1.00%
Duration of employee stock purchase plan as determined by the compensation committee	24 months
Duration for offering period, employee stock purchase plan	6 months
Employee stock purchase plan, number of purchase periods | Period	4
Maximum duration for purchase under employee stock purchase plan	1 year
Maximum duration of employee stock purchase plan	27 months
Percentage of purchase of common stock	85.00%
Percentage of common stock on the date of purchase	85.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	$ 610	$ 402
Research and development expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	172	117
General and administrative expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	438	285
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	252	225
Restricted stock and restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	204	163
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	$ 154	$ 14

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Unrecognized Stock-based Compensation Expense, Net of Estimated Forfeitures, by Type of Award and Weighted-average Recognition Period (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	May 31, 2015	Feb. 20, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures		$ 62,000	$ 168,000
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	$ 2,045,000
Weighted-average Recognition Period	2 years 11 months 23 days
Restricted stock and restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	$ 599,000
Weighted-average Recognition Period	2 years 1 month 28 days

Stock-Based Compensation - Su37

Stock-Based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted stock [Member]	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Unvested, Beginning balance | shares	245,096
Shares, Unvested, Ending balance | shares	245,096
Weighted-Average Grant Date Fair Value, Unvested, Beginning balance | $ / shares	$ 2.53
Weighted-Average Grant Date Fair Value, Unvested, Ending balance | $ / shares	$ 2.53

Stock-Based Compensation - Su38

Stock-Based Compensation - Summary of Restricted Stock Units Activity (Detail) - Restricted stock units [Member]	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Unvested, Beginning balance | shares	46,250
Shares, Granted | shares	90,000
Shares, Unvested, Ending balance | shares	136,250
Weighted-Average Grant Date Fair Value, Unvested, Beginning balance | $ / shares	$ 5.50
Weighted-Average Grant Date Fair Value, Granted | $ / shares	4.65
Weighted-Average Grant Date Fair Value, Unvested, Ending balance | $ / shares	$ 4.94

Stock-Based Compensation - Su39

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding beginning balance, Shares Subject to Stock Options	1,575,864
Granted, Shares Subject to Stock Options	455,000
Exercised, Shares Subject to Stock Options	(44,393)	0
Cancelled, Shares Subject to Stock Options	(18,750)
Options outstanding ending balance, Shares Subject to Stock Options	1,967,721
Options exercisable, Shares Subject to Stock Options	783,546
Options outstanding beginning balance, Weighted-Average Exercise Price	$ 2.68
Granted, Weighted-Average Exercise Price	4.60
Exercised, Weighted-Average Exercise Price	1.65
Cancelled, Weighted-Average Exercise Price	1.91
Options outstanding ending balance, Weighted-Average Exercise Price	3.16
Options exercisable, Weighted-Average Exercise Price	$ 3.49
Options outstanding, Weighted-Average Remaining Contractual Term	8 years 7 months 28 days
Options exercisable, Weighted-Average Remaining Contractual Term	8 years 25 days
Exercised, Aggregate Intrinsic Value	$ 157,000
Options outstanding, Aggregate Intrinsic Value	3,592,000
Options exercisable, Aggregate Intrinsic Value	$ 1,558,000

Stock-Based Compensation - Sc40

Stock-Based Compensation - Schedule of Weighted Average Assumptions using Black-Scholes Option Pricing Model (Detail)	3 Months Ended
	Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Expected volatility	81.33%
Expected term (in years)	6 years 1 month 6 days
Risk-free interest rate	2.47%
Expected dividend yield	0.00%

Warrants - Additional Informati

Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Dec. 11, 2017	Jun. 14, 2017	Apr. 13, 2016	May 04, 2015	Mar. 31, 2018	Jan. 16, 2018	Jun. 19, 2017	May 08, 2017
Class of Warrant or Right [Line Items]
Issuance of shares of common stock	5,900,000		7,500,000
Exercise price of warrant			$ 1.50		$ 10
Warrant description					The warrant is exercisable for cash or on a cashless basis at a per share exercise price equal to $10.00 commencing on April 28, 2016, one year following the date of the prospectus filed with the SEC relating to the IPO, and expiring on April 28, 2020. The warrant also provides for registration rights upon request, under certain circumstances. The piggyback registration right provided in connection with the warrant will terminate on April 28, 2022.
Warrant termination date					Apr. 28, 2022
Initial public offering, expiration date					Apr. 28, 2020
Warrants sold			7,500,000
Common stock, price per share			$ 1.25
Warrants expiry date					Apr. 13, 2021
Public offering price per warrant			$ 0.01
Warrants outstanding					6,691,443
Warrants exercised					1,481,256
Securities Purchase Agreement [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding					1,046,895
Warrants exercised					940,442
Public offering price per share and per warrant		$ 1.15					$ 1.15
Unexercised warrants						1,987,337
Loan and Security Agreement [Member] | Minimum [Member]
Class of Warrant or Right [Line Items]
Beneficial ownership of company's common stock			49.90%					49.90%
Ligand [Member] | Loan and Security Agreement [Member]
Class of Warrant or Right [Line Items]
Issuance of shares of common stock			960,000
Exercise price of warrant			$ 1.50
Warrants sold			960,000
Warrants expiry date					Apr. 13, 2021
Repayments of notes payable in stock			$ 1.2
Over-Allotment Option [Member]
Class of Warrant or Right [Line Items]
Issuance of shares of common stock	769,565
Warrants sold			1,125,000
Common stock, price per share	$ 2.50
Private Placement and Registered Direct Offering [Member] | Securities Purchase Agreement [Member]
Class of Warrant or Right [Line Items]
Exercise price of warrant		$ 1.30
Warrants expiry date		Dec. 19, 2022			Dec. 19, 2022
Number of warrants issued for common stock		0.75
Warrants exercisable date		Dec. 19, 2017			Dec. 19, 2017
Percentage of warrant exercise beneficial ownership limitation of common stock outstanding minimum		4.99%
Prior notice period of increase beneficial ownership limitation		61 days
Percentage of minimum beneficial ownership limitation		9.99%
Description of beneficial ownership limitation					Each holder of a Warrant will not have the right to exercise any portion of its Warrant if the holder, together with its affiliates, would beneficially own in excess of 4.99% of the number of shares of common stock outstanding immediately after giving effect to such exercise (the “Beneficial Ownership Limitation”); provided, however, that upon 61 days’ prior notice to the Company, the holder may increase the Beneficial Ownership Limitation; however, in no event shall the Beneficial Ownership Limitation exceed 9.99%.
Common stock warrants [Member]
Class of Warrant or Right [Line Items]
Issuance of shares of common stock				82,500
Common Stock [Member] | Private Placement and Registered Direct Offering [Member] | Securities Purchase Agreement [Member]
Class of Warrant or Right [Line Items]
Issuance of shares of common stock		3,749,783
Common Stock [Member] | Private Placement and Registered Direct Offering [Member] | Maximum [Member] | Securities Purchase Agreement [Member]
Class of Warrant or Right [Line Items]
Warrants sold		2,812,337

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Jul. 07, 2015ft²
Commitments And Contingencies [Line Items]
Rent expense	$ 62,000	$ 62,000
Sublease [Member]
Commitments And Contingencies [Line Items]
Future minimum payments pursuant to sublease	$ 107,000
California [Member] | Sublease [Member]
Commitments And Contingencies [Line Items]
Area of subleased premises | ft²			7,049