Viking Therapeutics (VKTX) 10-Q 7 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
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	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		71,459,857

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 169,506	$ 8,988
Short-term investments – available for sale	134,656	11,587
Prepaid clinical trial and preclinical study costs	1,847	887
Prepaid expenses and other current assets	607	389
Total current assets	306,616	21,851
Deferred public offering and other financing costs	180	270
Total assets	306,796	22,121
Current liabilities:
Accounts payable	1,215	1,529
Other accrued liabilities	3,528	2,257
Accrued interest, current		22
Convertible notes payable, current (net of discount of $0 and $404 at September 30, 2018 and December 31, 2017, respectively)		3,451
Debt conversion feature liability, current		1,398
Total current liabilities	4,743	8,657
Total liabilities	4,743	8,657
Commitments and contingencies (Note 8)
Stockholders’ equity:
Preferred stock, $0.00001 par value: 10,000,000 shares authorized at September 30, 2018 and December 31, 2017; no shares issued and outstanding at September 30, 2018 and December 31, 2017
Common stock, $0.00001 par value: 300,000,000 shares authorized at September 30, 2018 and December 31, 2017; 71,284,604 and 35,817,104 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	1
Additional paid-in capital	399,847	94,339
Accumulated deficit	(97,678)	(80,855)
Accumulated other comprehensive loss	(117)	(20)
Total stockholders’ equity	302,053	13,464
Total liabilities and stockholders’ equity	$ 306,796	$ 22,121

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Convertible notes payable, discount, current portion	$ 0	$ 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	71,284,604	35,817,104
Common stock, shares outstanding	71,284,604	35,817,104

Statements of Operations and Co

Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenues	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	5,687	3,465	13,951	10,708
General and administrative	1,707	1,227	5,173	3,935
Total operating expenses	7,394	4,692	19,124	14,643
Loss from operations	(7,394)	(4,692)	(19,124)	(14,643)
Other income (expense):
Change in fair value of debt conversion feature liability		(1,136)	1,398	(288)
Amortization of debt discount		(256)	(404)	(1,024)
Amortization of financing costs	(30)	(17)	(90)	(537)
Interest income (expense), net	824	2	1,397	(1)
Total other income (expense), net	794	(1,407)	2,301	(1,850)
Net loss	(6,600)	(6,099)	(16,823)	(16,493)
Other comprehensive loss, net of tax:
Unrealized gain (loss) on securities	30	2	(97)	3
Comprehensive loss	$ (6,570)	$ (6,097)	$ (16,920)	$ (16,490)
Basic and diluted net loss per common share	$ (0.11)	$ (0.22)	$ (0.32)	$ (0.67)
Weighted-average shares used to compute basic and diluted net loss per share	61,232	27,470	52,943	24,666

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital	Retained Earnings	AOCI Attributable to Parent
Balance at Dec. 31, 2016	$ 8,043		$ 68,327	$ (60,277)	$ (7)
Balance (in shares) at Dec. 31, 2016		20,823,873
Employee stock-based compensation	1,073		1,073
Employee stock-based compensation (in shares)		(10,655)
Issuance of common stock under employee stock plans	20		20
Issuance of common stock under employee stock plans (in shares)		33,012
Sale of common stock, net of issuance costs	9,580		9,580
Sale of common stock, net of issuance costs (in shares)		7,652,617
Unrealized gain (loss) on investments	3				3
Net loss	(16,493)			(16,493)
Balance at Sep. 30, 2017	2,226		79,000	(76,770)	(4)
Balance (in shares) at Sep. 30, 2017		28,498,847
Balance at Jun. 30, 2017	6,588		77,265	(70,671)	(6)
Balance (in shares) at Jun. 30, 2017		27,697,284
Employee stock-based compensation	344		344
Employee stock-based compensation (in shares)		(219)
Issuance of common stock under employee stock plans (in shares)		500
Sale of common stock, net of issuance costs	1,391		1,391
Sale of common stock, net of issuance costs (in shares)		801,282
Unrealized gain (loss) on investments	2				2
Net loss	(6,099)			(6,099)
Balance at Sep. 30, 2017	2,226		79,000	(76,770)	(4)
Balance (in shares) at Sep. 30, 2017		28,498,847
Balance at Dec. 31, 2017	13,464		94,339	(80,855)	(20)
Balance (in shares) at Dec. 31, 2017		35,817,104
Employee stock-based compensation	1,890		1,890
Employee stock-based compensation (in shares)		(22,546)
Issuance of common stock under employee stock plans	470		470
Issuance of common stock under employee stock plans (in shares)		257,289
Issuance of common stock from warrant exercises	7,167		7,167
Issuance of common stock from warrant exercises (in shares)		4,457,757
Sale of common stock, net of issuance costs	295,982	$ 1	295,981
Sale of common stock, net of issuance costs (in shares)		30,775,000
Unrealized gain (loss) on investments	(97)				(97)
Net loss	(16,823)			(16,823)
Balance at Sep. 30, 2018	302,053	$ 1	399,847	(97,678)	(117)
Balance (in shares) at Sep. 30, 2018		71,284,604
Balance at Jun. 30, 2018	140,363	$ 1	231,587	(91,078)	(147)
Balance (in shares) at Jun. 30, 2018		60,652,794
Employee stock-based compensation	747		747
Employee stock-based compensation (in shares)		(205)
Issuance of common stock under employee stock plans	157		157
Issuance of common stock under employee stock plans (in shares)		21,604
Issuance of common stock from warrant exercises	2,342		2,342
Issuance of common stock from warrant exercises (in shares)		1,110,411
Sale of common stock, net of issuance costs	165,014		165,014
Sale of common stock, net of issuance costs (in shares)		9,500,000
Unrealized gain (loss) on investments	30				30
Net loss	(6,600)			(6,600)
Balance at Sep. 30, 2018	$ 302,053	$ 1	$ 399,847	$ (97,678)	$ (117)
Balance (in shares) at Sep. 30, 2018		71,284,604

Statements of Cash Flows (Unaud

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net loss	$ (16,823)	$ (16,493)
Adjustments to reconcile net loss to net cash used in operating activities
Amortization of debt discount on notes payable	404	1,024
Amortization of investment premiums	144	79
Amortization of financing costs	90	537
Amortization of non-cash clinical trial costs	541	648
Change in fair value of debt conversion feature liability	(1,398)	288
Stock-based compensation	1,991	1,088
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,823)	299
Accounts payable	(333)	232
Accrued expenses	1,131	1,487
Net cash used in operating activities	(16,076)	(10,811)
Cash flows from investing activities
Purchases of investments	(167,290)	(13,106)
Proceeds from maturities of investments	43,952	15,772
Net cash (used in) provided by investing activities	(123,338)	2,666
Cash flows from financing activities
Proceeds from issuances of common stock, net of underwriting discounts and commissions	296,607	7,832
Public offering and financing costs	(482)	(124)
Repayment of convertible notes payable	(3,833)	(77)
Value of shares withheld related to employee tax withholding	(101)	(14)
Proceeds from warrant and option exercises and stock issuance under employee stock purchase plan	7,741	20
Net cash provided by financing activities	299,932	7,637
Net increase in cash and cash equivalents	160,518	(508)
Cash and cash equivalents beginning of period	8,988	3,076
Cash and cash equivalents end of period	169,506	2,568
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	81	123
Supplemental disclosure of non-cash investing and financing transactions
Shares issued		1,800
Unpaid deferred public offering and other financing costs	$ 283	220
Lincoln Park Agreement [Member]
Supplemental disclosure of non-cash investing and financing transactions
Shares issued		$ 180

Organization, Liquidity and Man

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 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 September 30, 2018, statements of operations for the three and nine months ended September 30, 2018 and 2017, statements of stockholders’ equity for the three and nine months ended September 30, 2018 and 2017 and statements of cash flows for the nine months ended September 30, 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 September 30, 2018, the results of operations for the three and nine months ended September 30, 2018 and 2017, the statements of stockholders’ equity for the three and nine months ended September 30, 2018 and 2017 and cash flows for the nine months ended September 30, 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 and nine months ended September 30, 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, through May 21, 2018, and accounting for certain commitments. Actual results could differ from those estimates. Recent Accounting Pronouncements Adopted Accounting Standards In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), 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 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 In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation (Topic 718) Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases 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 (“ 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. For purposes of this calculation, the Company currently does not have any deemed common share equivalents; therefore, its basic and diluted net loss per share calculations are the same. The following table presents the computation of basic and diluted net loss per common share (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Numerator: Net loss attributable to common stockholders $ (6,600 ) $ (6,099 ) $ (16,823 ) $ (16,493 ) Denominator: Weighted-average common shares outstanding 61,414,775 27,714,880 53,154,530 24,939,198 Less: Weighted-average shares subject to repurchase (183,095 ) (245,096 ) (211,257 ) (273,257 ) Denominator for basic net loss per share 61,231,680 27,469,784 52,943,273 24,665,941 Net loss per share: Basic and diluted $ (0.11 ) $ (0.22 ) $ (0.32 ) $ (0.67 ) 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 September 30, 2018 2017 Common stock warrants 6,744,779 12,479,837 Restricted stock units 138,125 56,250 Common stock subject to repurchase 183,095 245,096 Common stock options 2,014,047 1,589,894 Shares issuable upon conversion of debt — 2,941,206 9,080,046 17,312,283 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	9 Months Ended
	Sep. 30, 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 September 30, 2018 and December 31, 2017, the Company’s investments were in government money market funds, certificates of deposit, commercial paper and corporate debt securities. There were no sales of available-for-sale securities during the three and nine months ended September 30, 2018 or during the year ended December 31, 2017. Investments classified as available-for-sale as of September 30, 2018 consisted of the following (in thousands): As of September 30, 2018 Amortized Cost Gross Unrealized Gains (1) Gross Unrealized Losses (1) Aggregate Estimated Fair Value Commercial paper (2) $ 3,458 $ — $ — $ 3,458 Corporate debt securities (2) 131,314 — (116 ) 131,198 $ 134,772 $ — $ (116 ) $ 134,656 (1) Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At September 30, 2018, there were three securities in an unrealized gain position and there were 111 securities in an unrealized loss position. These unrealized losses were less than $10,000 individually and $116,000 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 September 30, 2018, none of these securities were classified as cash and cash equivalents on the Company’s balance sheet, and $7.5 million of these securities were scheduled to mature outside of one year at the time of purchase. 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	9 Months Ended
	Sep. 30, 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 and accounts payable and, through May 21, 2018, 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 September 30, 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 as of December 31, 2017. There was no similar financial liability as of September 30, 2018. The fair value of the debt conversion feature, current as of 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 was 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 September 30, 2018, the Company’s investments were in government money market funds, certificates of deposit, commercial paper and corporate debt securities. The fair values of the Company’s financial instruments are presented below (in thousands): Fair Value Measurements at September 30, 2018 Total Level 1 Level 2 Level 3 Financial assets carried at fair value: Cash equivalents: Government money market funds $ 161,199 $ 161,199 $ — $ — Commercial paper, available-for-sale 2,990 — 2,990 — Corporate debt securities, available-for-sale 4,074 — 4,074 — Short-term investments Commercial paper, available-for-sale 3,458 — 3,458 — Corporate debt securities, available-for-sale 131,198 — 131,198 — Total financial assets $ 302,919 $ 161,199 $ 141,720 $ — 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 and nine months ended September 30, 2018 and 2017 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Debt conversion feature: Beginning balance $ — $ 894 $ 1,398 $ 731 Adjustments resulting from modification of debt — — — $ 1,011 Adjustments resulting from changes in fair value recognized in earnings — 1,136 (1,398 ) 288 Ending balance $ — $ 2,030 $ — $ 2,030 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 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 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	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Convertible Notes Payable	4. Convertible Notes Payable Convertible notes payable consisted of the following (in thousands): September 30, 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 Conversion payoff value — 1,938 Discount on notes payable, current — (404 ) Convertible notes payable, current (net of discount) $ — $ 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, 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. On May 8, 2017, the Company entered into the Third 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 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. On May 21, 2018, the Company repaid the entire remaining balance of $3.9 million due on the Ligand Note in cash. During the three and nine months ended September 30, 2018, the Company recorded $0 and $38,000 of interest expense, respectively, $0 and $404,000 of amortization of debt discount, respectively, and $0 and $1.4 million as other income related to the decrease in the fair value of the debt conversion feature liability, respectively. During the three and nine months ended September 30, 2017, the Company recorded $24,000 and $73,000 of interest expense, respectively, $256,000 and $1.0 million of amortization of debt discount, respectively, and an expense of $1.1 million and $288,000 related to the increase in the fair value of the debt conversion feature liability, respectively.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 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 September 30, 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 and nine months ended September 30, 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. 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 and nine months ended September 30, 2018, the Company recorded amortization expense of $64,000 and $541,000, respectively, in clinical study costs related to the SPA with PoC. During the three and nine months ended September 30, 2017, the Company recorded amortization expense of $249,000 and $648,000, respectively. The remaining prepaid balance of $265,000 was recorded on the balance sheet as of September 30, 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. On June 11, 2018, the Company completed an underwritten public offering of common stock (the “June 2018 Offering”) pursuant to the Shelf Registration Statement and a registration statement on Form S-3MEF (File No. 333-225479) filed pursuant to Rule 462(b) of the Securities Act of 1933, as amended. In the June 2018 Offering, the Company sold 8,625,000 shares of the Company’s common stock at a public offering price of $9.00 per share of common stock. Upon the closing of the June 2018 Offering on June 11, 2018, the Company received net proceeds of $72.3 million, after deducting underwriting discounts, commissions and other offering expenses. On September 25, 2018, the Company completed an underwritten public offering of common stock (the “September 2018 Offering”) pursuant to the Company’s universal shelf registration statement on Form S-3 (File No. 333-226133), filed with the SEC on July 11, 2018 and declared effective on July 19, 2018. In the September 2018 Offering, the Company sold 9,500,000 shares of the Company’s common stock at a public offering price of $18.50 per share. Upon the closing of the September 2018 Offering on September 25, 2018, the Company received net proceeds of $165.0 million, after deducting underwriting discounts, commissions and other offering expenses. During the nine months ended September 30, 2018 and 2017, and in accordance with the Company’s 2014 Employee Stock Purchase Plan (the “ESPP”), the Company issued an aggregate of 72,597 and 19,887 shares of its common stock to certain employees, respectively.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 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 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 September 30, 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 and nine months ended September 30, 2018 and 2017, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Stock-based compensation expense by type of award: Stock options $ 447 $ 154 $ 1,018 $ 529 Restricted stock and restricted stock units 79 180 403 521 Employee stock purchase plan 224 10 570 38 Total stock-based compensation expense included in expenses $ 750 $ 344 $ 1,991 $ 1,088 Stock-based compensation expense by line item: Research and development expenses $ 325 $ 85 $ 720 $ 302 General and administrative expenses 425 259 1,271 786 Total stock-based compensation expense included in expenses $ 750 $ 344 $ 1,991 $ 1,088 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 September 30, 2018 Unrecognized Expense, Net of Estimated Forfeitures Weighted- average Recognition Period (in years) Type of award: Stock options $ 2,378 2.59 Restricted stock and restricted stock units $ 541 2.15 The following table is a summary of restricted stock activity during the nine months ended September 30, 2018: Shares of Restricted Stock Weighted- Average Grant Date Fair Value Unvested at December 31, 2017 245,096 $ 2.53 Granted — $ — Vested (62,001 ) $ 9.49 Forfeited — $ — Unvested at September 30, 2018 183,095 $ 0.17 The following table summarizes restricted stock unit activity during the nine months ended September 30, 2018: Shares Subject to Restricted Stock Units Weighted- Average Grant Date Value Unvested at December 31, 2017 46,250 $ 5.50 Granted 105,000 $ 5.34 Vested (13,125 ) $ 8.78 Forfeited — $ — Unvested September 30, 2018 138,125 $ 5.07 The following table summarizes stock option activity during the nine months ended September 30, 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 628,500 $ 5.89 Exercised (171,567 ) $ 2.31 1,332,000 Cancelled (18,750 ) $ 1.91 Options outstanding at September 30, 2018 2,014,047 $ 3.72 8.29 27,584,000 Options exercisable at September 30, 2018 807,091 $ 3.99 7.60 10,836,000 The Company received $396,000 in cash proceeds from exercises of stock options during the nine months ended September 30, 2018. There were no option exercises during the nine months ended September 30, 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 nine months ended September 30, 2018 was $4.11. As stock-based compensation expense recognized is based on options ultimately expected to vest, the fair value of each employee option grant during the nine months ended September 30, 2018 was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions: Nine Months Ended September 30, 2018 Expected volatility 80.86 % Expected term (in years) 6.00 Risk-free interest rate 2.55 % 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 September 30, 2018, no excess tax benefits for the tax deductions related to stock-based awards were recognized in the Statements of Operations.

Warrants

Warrants	9 Months Ended
	Sep. 30, 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 was 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. All 82,500 warrants were exercised during the three months ended September 30, 2018. The warrant also provided for registration rights upon request, under certain circumstances. The piggyback registration right provided in connection with the warrant was to terminate on April 28, 2022. On April 13, 2016, pursuant to an underwritten public offering (the “April 2016 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 April 2016 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 September 30, 2018, warrants to purchase an aggregate of 4,899,384 shares were outstanding and 902,911 and 3,273,315 warrants were exercised during the three and nine months ended September 30, 2018, respectively. 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	9 Months Ended
	Sep. 30, 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 $63,000 and $64,000 for the three months ended September 30, 2018 and 2017, respectively. Rent expense was $189,000 and $185,000 for the nine months ended September 30, 2018 and 2017, respectively. In September 2018, the Company renewed the Sublease for one additional month through October 31, 2018. Future minimum payments pursuant to the Sublease are $22,000 in the aggregate through October 31, 2018, the remaining term of the Sublease. Additionally, on May 25, 2018, the Company entered into an Office Lease (the “Lease”) with Kilroy Realty, L.P. (the “Landlord”). The Lease is for approximately 7,149 rentable square feet of space located at the Premises. The Premises will continue to be the Company’s corporate headquarters. The Lease commenced on November 1, 2018 and will expire on January 31, 2022, unless terminated earlier in accordance with the terms of the Lease (the “Term”). Monthly base rent payments due under the Lease for the Premises will be $26,808.75, subject to annual increases of 3.0% during the term of the Lease. The Company is also responsible for certain other costs under the Lease, including electricity and utility expenses and certain repair and maintenance obligations. The Lease provides the Company with an option to extend the term of the lease for a period of three years beyond the Term. If the option is exercised, the renewal term will be upon the same terms and conditions as the original Term, except that the base rent will be equal to the prevailing market rate as determined pursuant to the terms of the Lease. Future minimum payments pursuant to the Lease are as follows (in thousands) As of September 30, 2018: 2018 $ 27 2019 270 2020 333 2021 343 2022 29 Total minimum lease payments $ 1,002

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 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 September 30, 2018, and events which occurred subsequent to September 30, 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 M_2

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 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 September 30, 2018, statements of operations for the three and nine months ended September 30, 2018 and 2017, statements of stockholders’ equity for the three and nine months ended September 30, 2018 and 2017 and statements of cash flows for the nine months ended September 30, 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 September 30, 2018, the results of operations for the three and nine months ended September 30, 2018 and 2017, the statements of stockholders’ equity for the three and nine months ended September 30, 2018 and 2017 and cash flows for the nine months ended September 30, 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 and nine months ended September 30, 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, through May 21, 2018, 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 Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), 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 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 In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation (Topic 718) Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases
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 (“ 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. For purposes of this calculation, the Company currently does not have any deemed common share equivalents; therefore, its basic and diluted net loss per share calculations are the same. The following table presents the computation of basic and diluted net loss per common share (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Numerator: Net loss attributable to common stockholders $ (6,600 ) $ (6,099 ) $ (16,823 ) $ (16,493 ) Denominator: Weighted-average common shares outstanding 61,414,775 27,714,880 53,154,530 24,939,198 Less: Weighted-average shares subject to repurchase (183,095 ) (245,096 ) (211,257 ) (273,257 ) Denominator for basic net loss per share 61,231,680 27,469,784 52,943,273 24,665,941 Net loss per share: Basic and diluted $ (0.11 ) $ (0.22 ) $ (0.32 ) $ (0.67 ) 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 September 30, 2018 2017 Common stock warrants 6,744,779 12,479,837 Restricted stock units 138,125 56,250 Common stock subject to repurchase 183,095 245,096 Common stock options 2,014,047 1,589,894 Shares issuable upon conversion of debt — 2,941,206 9,080,046 17,312,283
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 M_3

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 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 share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Numerator: Net loss attributable to common stockholders $ (6,600 ) $ (6,099 ) $ (16,823 ) $ (16,493 ) Denominator: Weighted-average common shares outstanding 61,414,775 27,714,880 53,154,530 24,939,198 Less: Weighted-average shares subject to repurchase (183,095 ) (245,096 ) (211,257 ) (273,257 ) Denominator for basic net loss per share 61,231,680 27,469,784 52,943,273 24,665,941 Net loss per share: Basic and diluted $ (0.11 ) $ (0.22 ) $ (0.32 ) $ (0.67 )
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 September 30, 2018 2017 Common stock warrants 6,744,779 12,479,837 Restricted stock units 138,125 56,250 Common stock subject to repurchase 183,095 245,096 Common stock options 2,014,047 1,589,894 Shares issuable upon conversion of debt — 2,941,206 9,080,046 17,312,283

Investments in Marketable Sec_2

Investments in Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Summary of Investments Classified As Available-For-Sale Securities	Investments classified as available-for-sale as of September 30, 2018 consisted of the following (in thousands): As of September 30, 2018 Amortized Cost Gross Unrealized Gains (1) Gross Unrealized Losses (1) Aggregate Estimated Fair Value Commercial paper (2) $ 3,458 $ — $ — $ 3,458 Corporate debt securities (2) 131,314 — (116 ) 131,198 $ 134,772 $ — $ (116 ) $ 134,656 (1) Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At September 30, 2018, there were three securities in an unrealized gain position and there were 111 securities in an unrealized loss position. These unrealized losses were less than $10,000 individually and $116,000 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 September 30, 2018, none of these securities were classified as cash and cash equivalents on the Company’s balance sheet, and $7.5 million of these securities were scheduled to mature outside of one year at the time of purchase. 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 Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2018 Total Level 1 Level 2 Level 3 Financial assets carried at fair value: Cash equivalents: Government money market funds $ 161,199 $ 161,199 $ — $ — Commercial paper, available-for-sale 2,990 — 2,990 — Corporate debt securities, available-for-sale 4,074 — 4,074 — Short-term investments Commercial paper, available-for-sale 3,458 — 3,458 — Corporate debt securities, available-for-sale 131,198 — 131,198 — Total financial assets $ 302,919 $ 161,199 $ 141,720 $ — 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 and nine months ended September 30, 2018 and 2017 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Debt conversion feature: Beginning balance $ — $ 894 $ 1,398 $ 731 Adjustments resulting from modification of debt — — — $ 1,011 Adjustments resulting from changes in fair value recognized in earnings — 1,136 (1,398 ) 288 Ending balance $ — $ 2,030 $ — $ 2,030
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 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)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of Convertible Notes Payable	Convertible notes payable consisted of the following (in thousands): September 30, 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 Conversion payoff value — 1,938 Discount on notes payable, current — (404 ) Convertible notes payable, current (net of discount) $ — $ 3,451

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2018
Summary of Stock-based Compensation Expense Recognized	During the three and nine months ended September 30, 2018 and 2017, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Stock-based compensation expense by type of award: Stock options $ 447 $ 154 $ 1,018 $ 529 Restricted stock and restricted stock units 79 180 403 521 Employee stock purchase plan 224 10 570 38 Total stock-based compensation expense included in expenses $ 750 $ 344 $ 1,991 $ 1,088 Stock-based compensation expense by line item: Research and development expenses $ 325 $ 85 $ 720 $ 302 General and administrative expenses 425 259 1,271 786 Total stock-based compensation expense included in expenses $ 750 $ 344 $ 1,991 $ 1,088
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 September 30, 2018 Unrecognized Expense, Net of Estimated Forfeitures Weighted- average Recognition Period (in years) Type of award: Stock options $ 2,378 2.59 Restricted stock and restricted stock units $ 541 2.15
Summary of Stock Option Activity	The following table summarizes stock option activity during the nine months ended September 30, 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 628,500 $ 5.89 Exercised (171,567 ) $ 2.31 1,332,000 Cancelled (18,750 ) $ 1.91 Options outstanding at September 30, 2018 2,014,047 $ 3.72 8.29 27,584,000 Options exercisable at September 30, 2018 807,091 $ 3.99 7.60 10,836,000
Schedule of Weighted Average Assumptions using Black-Scholes Option Pricing Model	the fair value of each employee option grant during the nine months ended September 30, 2018 was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions: Nine Months Ended September 30, 2018 Expected volatility 80.86 % Expected term (in years) 6.00 Risk-free interest rate 2.55 % Expected dividend yield 0 %
Restricted stock [Member]
Summary of Stock Activity	The following table is a summary of restricted stock activity during the nine months ended September 30, 2018: Shares of Restricted Stock Weighted- Average Grant Date Fair Value Unvested at December 31, 2017 245,096 $ 2.53 Granted — $ — Vested (62,001 ) $ 9.49 Forfeited — $ — Unvested at September 30, 2018 183,095 $ 0.17
Restricted stock units [Member]
Summary of Stock Activity	The following table summarizes restricted stock unit activity during the nine months ended September 30, 2018: Shares Subject to Restricted Stock Units Weighted- Average Grant Date Value Unvested at December 31, 2017 46,250 $ 5.50 Granted 105,000 $ 5.34 Vested (13,125 ) $ 8.78 Forfeited — $ — Unvested September 30, 2018 138,125 $ 5.07

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Minimum Payments for Lease	Future minimum payments pursuant to the Lease are as follows (in thousands) As of September 30, 2018: 2018 $ 27 2019 270 2020 333 2021 343 2022 29 Total minimum lease payments $ 1,002

Organization, Liquidity and M_4

Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 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 M_5

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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net loss attributable to common stockholders	$ (6,600)	$ (6,099)	$ (16,823)	$ (16,493)
Denominator:
Weighted-average common shares outstanding	61,414,775	27,714,880	53,154,530	24,939,198
Less: Weighted-average shares subject to repurchase	(183,095)	(245,096)	(211,257)	(273,257)
Denominator for basic net loss per share	61,231,680	27,469,784	52,943,273	24,665,941
Net loss per share:
Basic and diluted	$ (0.11)	$ (0.22)	$ (0.32)	$ (0.67)

Organization, Liquidity and M_6

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	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded in calculation of diluted net loss per share	9,080,046	17,312,283
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	6,744,779	12,479,837
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	138,125	56,250
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	183,095	245,096
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	2,014,047	1,589,894
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		2,941,206

Investments in Marketable Sec_3

Investments in Marketable Securities - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Available For Sale Securities [Abstract]
Proceeds from sales of available-for-sale securities	$ 0	$ 0	$ 0

Investments in Marketable Sec_4

Investments in Marketable Securities - Summary of Investments Classified As Available-For-Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 134,772	$ 11,606
Gross Unrealized Losses	(116)	(19)
Aggregate Estimated Fair Value	134,656	11,587
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,458
Aggregate Estimated Fair Value	3,458
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		249
Aggregate Estimated Fair Value		249
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	131,314	11,357
Gross Unrealized Losses	(116)	(19)
Aggregate Estimated Fair Value	$ 131,198	$ 11,338

Investments in Marketable Sec_5

Investments in Marketable Securities - Summary of Investments Classified As Available-For-Sale Securities (Parenthetical) (Detail)	Sep. 30, 2018USD ($)Security	Dec. 31, 2017USD ($)Security
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized gain position | Security	3
Number of securities in unrealized loss position | Security	111	29
Unrealized losses, aggregate	$ 116,000	$ 19,000
Short-term investments – available for sale	134,656,000	11,587,000
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments – available for sale	3,458,000
Short-term investments classified as available-for-sale, noncurrent	7,500,000
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments – available for sale		249,000
Short-term investments classified as available-for-sale, noncurrent		0
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, aggregate	116,000	19,000
Short-term investments – available for sale	131,198,000	11,338,000
Short-term investments classified as available-for-sale, noncurrent	7,500,000	0
Cash equivalents [Member] | Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments – available for sale	0
Cash equivalents [Member] | Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments – available for sale		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	10,000	3,000
Unrealized losses, aggregate	$ 116,000	$ 19,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial assets carried at fair value:
Total financial assets	$ 302,919	$ 19,192
Financial liabilities carried at fair value:
Debt conversion feature - current		1,398
Total financial liabilities		1,398
Level 1 [Member]
Financial assets carried at fair value:
Total financial assets	161,199	6,361
Level 2 [Member]
Financial assets carried at fair value:
Total financial assets	141,720	12,831
Level 3 [Member]
Financial liabilities carried at fair value:
Debt conversion feature - current		1,398
Total financial liabilities		1,398
Government money market funds [Member]
Financial assets carried at fair value:
Cash equivalents, fair value disclosure	161,199	6,361
Government money market funds [Member] | Level 1 [Member]
Financial assets carried at fair value:
Cash equivalents, fair value disclosure	161,199	6,361
Commercial paper, available-for-sale [Member]
Financial assets carried at fair value:
Cash equivalents, fair value disclosure	2,990
Short-term investments, available for sale	3,458
Commercial paper, available-for-sale [Member] | Level 2 [Member]
Financial assets carried at fair value:
Cash equivalents, fair value disclosure	2,990
Short-term investments, available for sale	3,458
Corporate debt securities, available-for-sale [Member]
Financial assets carried at fair value:
Cash equivalents, fair value disclosure	4,074	1,244
Short-term investments, available for sale	131,198	11,338
Corporate debt securities, available-for-sale [Member] | Level 2 [Member]
Financial assets carried at fair value:
Cash equivalents, fair value disclosure	4,074	1,244
Short-term investments, available for sale	$ 131,198	11,338
Certificates of deposit, available-for-sale [Member]
Financial assets carried at fair value:
Short-term investments, available for sale		249
Certificates of deposit, available-for-sale [Member] | Level 2 [Member]
Financial assets carried at fair value:
Short-term investments, available for sale		$ 249

Fair Value of Financial Instr_4

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	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 894	$ 1,398	$ 731
Adjustments resulting from modification of debt			1,011
Adjustments resulting from changes in fair value recognized in earnings	1,136	$ (1,398)	288
Ending balance	$ 2,030		$ 2,030

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Schedule of Valuation Techniques and Significant Unobservable Inputs Used to Determine Fair Value of Significant Level 3 Liabilities (Detail) - Level 3 [Member] $ in Thousands	Dec. 31, 2017USD ($)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Assets	$ 0
Fair Value, Liabilities	$ 1,398
Debt Instrument, Type [Extensible List]	vktx:DebtConversionFeatureMember
Valuation Technique(s)	vktx:BlackScholesMertonOptionValuationModelMember
Volatility [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions	100
Risk Free Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Assumptions	1.46

Convertible Notes Payable - Sch

Convertible Notes Payable - Schedule of Convertible Notes Payable (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Conversion payoff value		$ 1,938
Discount on notes payable, current	$ 0	(404)
Convertible notes payable, current (net of discount)		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

Convertible Notes Payable - S_2

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 ($)	May 21, 2018	May 08, 2017	Jan. 22, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 21, 2016	May 21, 2014
Debt Instrument [Line Items]
Change in fair value of debt conversion feature liability					$ (1,136,000)	$ 1,398,000	$ (288,000)
Amortization of debt discount					256,000	404,000	1,024,000
Ligand Note [Member]
Debt Instrument [Line Items]
Required payment in cash for note obligation	$ 3,900,000
Change in fair value of debt conversion feature liability				$ 0	(1,100,000)	1,400,000	(288,000)
Interest expense				0	24,000	38,000	73,000
Amortization of debt discount				$ 0	256,000	$ 404,000	$ 1,000,000
Loan and Security Agreement [Member] | Ligand Note [Member]
Debt Instrument [Line Items]
Loan and security agreement, maturity date			May 21, 2017
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

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail)

Sep. 25, 2018USD ($)$ / sharesshares

Jun. 11, 2018USD ($)$ / sharesshares

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, 2016$ / sharesshares

May 31, 2015USD ($)$ / sharesshares

Feb. 28, 2014Tranche$ / sharesshares

Sep. 30, 2018USD ($)$ / sharesshares

Sep. 30, 2017USD ($)

Sep. 30, 2018USD ($)$ / sharesshares

Sep. 30, 2017USD ($)shares

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

Jul. 26, 2017USD ($)shares

Dec. 31, 2016USD ($)

Dec. 31, 2017$ / sharesshares

May 04, 2015$ / shares

Feb. 20, 2014USD ($)

Equity [Line Items]

Preferred stock, shares authorized

10,000,000

10,000,000

10,000,000

Preferred stock, par value | $ / shares

$ 0.00001

$ 0.00001

$ 0.00001

Preferred stock, shares outstanding

0

0

0

Common stock, shares authorized

300,000,000

300,000,000

300,000,000

Common stock, par value | $ / shares

$ 0.00001

$ 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 | $

$ 296,607,000

$ 7,832,000

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

Shares issued under ESPP

72,597

19,887

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] | June 2018 Offering [Member]

Equity [Line Items]

Common stock sold

8,625,000

Cash proceeds from common stock issuance | $

$ 72,300,000

Common stock, price per share | $ / shares

$ 9

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

Equity [Line Items]

Common stock sold

9,500,000

Cash proceeds from common stock issuance | $

$ 165,000,000

Common stock, price per share | $ / shares

$ 18.50

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 | $

$ 64,000

$ 249,000

$ 541,000

$ 648,000

Prepaid clinical study costs | $

$ 1,800,000

$ 265,000

$ 265,000

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

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

$ 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)	9 Months Ended
	Sep. 30, 2018USD ($)Period$ / sharesshares	Sep. 30, 2017shares	Apr. 28, 2015shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash proceeds from exercises of stock options | $	$ 396,000
Option exercises	171,567	0
Weighted average fair value of stock options granted to employees | $ / shares	$ 4.11
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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	$ 750	$ 344	$ 1,991	$ 1,088
Research and development expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	325	85	720	302
General and administrative expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	425	259	1,271	786
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	447	154	1,018	529
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	79	180	403	521
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	$ 224	$ 10	$ 570	$ 38

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 ($)	9 Months Ended
	Sep. 30, 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	$ 2,378,000
Weighted-average Recognition Period	2 years 7 months 2 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	$ 541,000
Weighted-average Recognition Period	2 years 1 month 24 days

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted stock [Member]	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Unvested, Beginning balance | shares	245,096
Shares, Vested | shares	(62,001)
Shares, Unvested, Ending balance | shares	183,095
Weighted-Average Grant Date Fair Value, Unvested, Beginning balance | $ / shares	$ 2.53
Weighted-Average Grant Date Fair Value, Vested | $ / shares	9.49
Weighted-Average Grant Date Fair Value, Unvested, Ending balance | $ / shares	$ 0.17

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Restricted Stock Units Activity (Detail) - Restricted stock units [Member]	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Unvested, Beginning balance | shares	46,250
Shares, Granted | shares	105,000
Shares, Vested | shares	(13,125)
Shares, Unvested, Ending balance | shares	138,125
Weighted-Average Grant Date Fair Value, Unvested, Beginning balance | $ / shares	$ 5.50
Weighted-Average Grant Date Fair Value, Granted | $ / shares	5.34
Weighted-Average Grant Date Fair Value, Vested | $ / shares	8.78
Weighted-Average Grant Date Fair Value, Unvested, Ending balance | $ / shares	$ 5.07

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 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	628,500
Exercised, Shares Subject to Stock Options	(171,567)	0
Cancelled, Shares Subject to Stock Options	(18,750)
Options outstanding ending balance, Shares Subject to Stock Options	2,014,047
Options exercisable, Shares Subject to Stock Options	807,091
Options outstanding beginning balance, Weighted-Average Exercise Price	$ 2.68
Granted, Weighted-Average Exercise Price	5.89
Exercised, Weighted-Average Exercise Price	2.31
Cancelled, Weighted-Average Exercise Price	1.91
Options outstanding ending balance, Weighted-Average Exercise Price	3.72
Options exercisable, Weighted-Average Exercise Price	$ 3.99
Options outstanding, Weighted-Average Remaining Contractual Term	8 years 3 months 14 days
Options exercisable, Weighted-Average Remaining Contractual Term	7 years 7 months 6 days
Exercised, Aggregate Intrinsic Value	$ 1,332,000
Options outstanding, Aggregate Intrinsic Value	27,584,000
Options exercisable, Aggregate Intrinsic Value	$ 10,836,000

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Weighted Average Assumptions using Black-Scholes Option Pricing Model (Detail)	9 Months Ended
	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Expected volatility	80.86%
Expected term (in years)	6 years
Risk-free interest rate	2.55%
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	Sep. 30, 2018	Sep. 30, 2018	Jan. 16, 2018	Jun. 19, 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 was 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.
Warrant termination date						Apr. 28, 2022
Initial public offering, expiration date						Apr. 28, 2020
Warrants exercised					902,911	3,273,315
Warrants sold			7,500,000		4,899,384	4,899,384
Common stock, price per share			$ 1.25
Warrants expiry date						Apr. 13, 2021
Public offering price per warrant			$ 0.01
Securities Purchase Agreement [Member]
Class of Warrant or Right [Line Items]
Warrants exercised					125,000	1,101,942
Warrants sold					885,395	885,395
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%
Ligand [Member] | Loan and Security Agreement [Member]
Class of Warrant or Right [Line Items]
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
Warrants exercised					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)	May 25, 2018USD ($)ft²	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Oct. 31, 2018USD ($)	Jul. 07, 2015ft²
Commitments And Contingencies [Line Items]
Rent expense		$ 63,000	$ 64,000	$ 189,000	$ 185,000
Future minimum payments pursuant to sublease		$ 1,002,000		$ 1,002,000
Operating lease option to extend term				3 years
Sublease [Member]
Commitments And Contingencies [Line Items]
Lease renewal term		1 month		1 month
Sublease [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Future minimum payments pursuant to sublease						$ 22,000
California [Member] | Sublease [Member]
Commitments And Contingencies [Line Items]
Area of lease premises | ft²							7,049
California [Member] | Office Lease [Member]
Commitments And Contingencies [Line Items]
Area of lease premises | ft²	7,149
Lease commencement date	Nov. 1, 2018
Lease expiration date	Jan. 31, 2022
Monthly base rent payments	$ 26,808.75
Percentage of rent increase under lease	3.00%

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Future Minimum Payments for Lease (Detail) $ in Thousands	Sep. 30, 2018USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2,018	$ 27
2,019	270
2,020	333
2,021	343
2,022	29
Total minimum lease payments	$ 1,002