VYNE Therapeutics (VYNE) 10-K 28 Feb 19 2018 FY Annual report Financial data

DEI Document

DEI Document - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 15, 2019	Jun. 30, 2018
Entity [Abstract]
Entity Registrant Name	MENLO THERAPEUTICS INC.
Entity Central Index Key	1,566,044
Trading Symbol	MNLO
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 Shell Company	false
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		23,258,184
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 88.6

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 49,510	$ 10,206
Short-term investments	86,740	49,295
Accounts receivable		786
Prepaid expenses and other current assets	3,250	3,574
Total current assets	139,500	63,861
Long-term investments		2,978
Property and equipment, net	146	28
Prepaid and other long-term assets	282
Total assets	139,928	66,867
Current liabilities:
Accounts payable	3,290	2,462
Accrued expenses and other current liabilities	6,254	3,559
Deferred revenue, current		1,796
Total current liabilities	9,544	7,817
Deferred revenue, long-term		6,735
Other non-current liabilities	7	22
Total liabilities	9,551	14,574
Commitments and contingencies (see Note 6)
Stockholders’ equity (deficit):
Preferred stock: $0.0001 par value; 20,000,000 shares and no shares authorized at December 31, 2018 and 2017, respectively; no shares issued and outstanding at December 31, 2018 and 2017, respectively
Common stock: $0.0001 par value; 300,000,000 shares and 55,000,000 shares authorized at December 31, 2018 and 2017, respectively; 23,233,184 and 5,298,593 shares issued and outstanding at December 31, 2018 and 2017, respectively	3	1
Additional paid-in capital	241,106	2,207
Accumulated other comprehensive loss	(96)	(51)
Accumulated deficit	(110,636)	(59,191)
Total stockholders’ equity (deficit)	130,377	(57,034)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 139,928	66,867
Series A Convertible Preferred Stock
Current liabilities:
Convertible preferred stock		14,183
Series B Convertible Preferred Stock
Current liabilities:
Convertible preferred stock		44,820
Series C Convertible Preferred Stock
Current liabilities:
Convertible preferred stock		$ 50,324

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Convertible preferred stock, par value per share (in USD per share)		$ 0.001
Convertible preferred stock authorized (shares)		28,322,761
Preferred stock, par value per share (in USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (shares)	20,000,000	0
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Common stock, par value per share (in USD per share)	$ 0.0001	$ 0.0001
Common stock authorized (shares)	300,000,000	55,000,000
Common stock issued (shares)	23,233,184	5,298,593
Common stock outstanding (shares)	23,233,184	5,298,593
Series A Convertible Preferred Stock
Convertible preferred stock, par value per share (in USD per share)	$ 0.001	$ 0.001
Convertible preferred stock authorized (shares)	0	14,300
Convertible preferred stock issued (shares)	0	14,300
Convertible preferred stock outstanding (shares)	0	14,300
Convertible preferred stock, liquidation value	$ 0	$ 14,300
Series B Convertible Preferred Stock
Convertible preferred stock, par value per share (in USD per share)	$ 0.001	$ 0.001
Convertible preferred stock authorized (shares)	0	14,106,583
Convertible preferred stock issued (shares)	0	14,106,583
Convertible preferred stock outstanding (shares)	0	14,106,583
Convertible preferred stock, liquidation value	$ 0	$ 45,000
Series C Convertible Preferred Stock
Convertible preferred stock, par value per share (in USD per share)	$ 0.001	$ 0.001
Convertible preferred stock authorized (shares)	0	14,201,878
Convertible preferred stock issued (shares)	0	11,854,463
Convertible preferred stock outstanding (shares)	0	11,854,463
Convertible preferred stock, liquidation value	$ 0	$ 50,500

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Collaboration and license revenue	$ 10,640	$ 4,582	$ 674
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 52,989	$ 29,007	$ 11,255
General and administrative	12,186	5,168	3,751
Total operating expenses	65,175	34,175	15,006
Loss from operations	(54,535)	(29,593)	(14,332)
Interest income and other expense, net	3,090	517	264
Net loss attributable to common stockholders	(51,445)	(29,076)	(14,068)
Other comprehensive loss:
Unrealized loss on available-for-sale securities	(45)	(25)	(26)
Comprehensive loss	$ (51,490)	$ (29,101)	$ (14,094)
Net loss attributable to common stockholder per share, basic and diluted	$ (2.37)	$ (5.69)	$ (2.82)
Weighted-average number of common shares used to compute basic and diluted net loss per share	21,668,689	5,108,121	4,987,133

Statement of Convertible Prefer

Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Series C Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Other Comprehensive Loss
Balance, beginning at Dec. 31, 2015	$ (15,953)				$ 1	$ 93	$ (16,047)
Preferred stock, beginning at Dec. 31, 2015		14,300	14,106,583
Preferred stock, beginning at Dec. 31, 2015		$ 14,183	$ 44,820
Common stock, beginning (shares) at Dec. 31, 2015					5,280,058
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of early exercised stock options	33					33
Stock-based compensation	573					573
Unrealized loss on available-for-sale securities	(26)							$ (26)
Net loss	(14,068)						(14,068)
Balance, ending at Dec. 31, 2016	(29,441)				$ 1	699	(30,115)	(26)
Preferred stock, ending at Dec. 31, 2016		14,300	14,106,583
Preferred stock, ending at Dec. 31, 2016		$ 14,183	$ 44,820
Common stock, ending (shares) at Dec. 31, 2016					5,280,058
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of preferred stock				$ 50,324
Issuance of preferred stock (shares)				11,854,463
Issuance of common stock onexercise of stock options	$ 34					34
Exercise of unvested stock options (shares)	18,535				18,535
Vesting of early exercised stock options	$ 22					22
Stock-based compensation	1,452					1,452
Unrealized loss on available-for-sale securities	(25)							(25)
Net loss	(29,076)						(29,076)
Balance, ending at Dec. 31, 2017	$ (57,034)				$ 1	2,207	(59,191)	(51)
Preferred stock, ending at Dec. 31, 2017		14,300	14,106,583	11,854,463
Preferred stock, ending at Dec. 31, 2017		$ 14,183	$ 44,820	$ 50,324
Common stock, ending (shares) at Dec. 31, 2017	5,298,593				5,298,593
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of preferred stock to common stock	$ 109,327	$ (14,183)	$ (44,820)	$ (50,324)	$ 1	109,326
Conversion of preferred stock to common stock (shares)		(14,300)	(14,106,583)	(11,854,463)	9,629,405
Issuance of common stock under public offering, net	125,417				$ 1	125,416
Issuance of common stock under public offering, net (shares)					8,050,000
Issuance of common stock onexercise of stock options	$ 496					496
Exercise of unvested stock options (shares)	255,186				255,186
Vesting of early exercised stock options	$ 23					23
Stock-based compensation	3,638					3,638
Unrealized loss on available-for-sale securities	(45)							(45)
Net loss	(51,445)						(51,445)
Balance, ending at Dec. 31, 2018	$ 130,377				$ 3	$ 241,106	$ (110,636)	$ (96)
Preferred stock, ending at Dec. 31, 2018		0	0	0
Common stock, ending (shares) at Dec. 31, 2018	23,233,184				23,233,184

Statement of Convertible Pref_2

Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Preferred Stock | Series C Convertible Preferred Stock
Preferred stock issuance costs	$ 173

Statement of Cash Flows

Statement of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (51,445,000)	$ (29,076,000)	$ (14,068,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	22,000	8,000	4,000
Amortization of premium on investment securities	(774,000)	66,000	158,000
Stock-based compensation expense	3,638,000	1,452,000	573,000
Gain on disposal of equipment		19,000	0
Accrued interest		31,000	0
Change in operating assets and liabilities:
Accounts receivable	786,000	(786,000)	0
Prepaid expenses and other current assets	324,000	(1,790,000)	(555,000)
Other long-term assets	(282,000)	66,000	(66,000)
Accounts payable	825,000	620,000	889,000
Accrued expenses and other current liabilities	2,719,000	2,976,000	466,000
Deferred revenue	(8,531,000)	(1,796,000)	10,327,000
Other non-current liabilities	(15,000)	(12,000)	7,000
Net cash used in operating activities	(52,733,000)	(28,222,000)	(2,265,000)
Investing activities
Purchase of property and equipment	(140,000)	(27,000)	(31,000)
Purchase of investments	(126,700,000)	(64,148,000)	(55,309,000)
Proceeds from sales of investments	5,100,000	6,000,000	3,600,000
Proceeds from maturities of investments	87,864,000	43,085,000	14,224,000
Net cash used in investing activities	(33,876,000)	(15,090,000)	(37,516,000)
Financing activities
Issuance of common stock pursuant to public offering, net of issuance costs	125,417,000
Proceeds from issuance of convertible preferred stock, net of issuance costs		50,324,000	0
Proceeds from the exercise of stock options	496,000	34,000	0
Deferred financing costs		(867,000)	0
Net cash provided by financing activities	125,913,000	49,491,000	0
Net increase (decrease) in cash and cash equivalents	39,304,000	6,179,000	(39,781,000)
Cash and cash equivalents at beginning of period	10,206,000	4,027,000	43,808,000
Cash and cash equivalents at end of period	49,510,000	10,206,000	4,027,000
Noncash financing activities
Conversion of preferred stock to common stock	$ 109,327,000
Deferred financing costs		$ 316,000	$ 0

Formation and Business of the C

Formation and Business of the Company	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Formation and Business of the Company	1. Formation and Business of the Company Menlo Therapeutics Inc. (the “Company”) is a late‑stage biopharmaceutical company focused on the development and commercialization of serlopitant for the treatment of pruritus, or itch, associated with various conditions such as prurigo nodularis, psoriasis and chronic pruritus of unknown origin, or CPUO. We believe that serlopitant, a highly selective small molecule inhibitor of the neurokinin 1 receptor, or NK1-R, given as a once-daily, oral tablet, has the potential to significantly alleviate pruritus. The Company was incorporated in Delaware in October 2011. Since commencing operations, the Company has devoted substantially all of its resources to developing its product candidate, serlopitant, including conducting clinical trials and providing general and administrative support for these operations. Initial Public Offering In January 2018, the Company completed its initial public offering (“IPO”) of shares of its common stock, pursuant to which the Company issued 8,050,000 shares of common stock, which includes 1,050,000 shares issued pursuant to the over-allotment option granted to its underwriters and received net proceeds of approximately $125.4 million, after deducting underwriting discounts, commissions and offering expenses. In connection with the completion of the Company's IPO, all shares of convertible preferred stock converted into 9,629,405 shares of common stock. Liquidity and Capital Resources The accompanying financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The financial statements do not reflect any adjustments relating to the recoverability and reclassification of assets and liabilities that might be necessary if the Company is unable to continue as a going concern. Since inception, the Company has incurred losses and negative cash flows from operations. For the 12 months ended December 31, 2018, the Company incurred a net loss of $51.4 million and used $52.7 million of cash in operations. As of December 31, 2018, the Company had cash, cash equivalents and investments of $136.3 million and an accumulated deficit of $110.6 million. Management expects to continue to incur additional substantial losses in the foreseeable future as a result of the Company’s research and development activities. Management plans to finance operations through equity or debt financings or other capital sources, including potential collaborations or other strategic transactions. There can be no assurances that, in the event that the Company requires additional financing, such financing will be available on terms which are favorable to the Company, or at all. If the Company is unable to raise additional funding to meet its working capital needs in the future, it will be forced to delay or reduce the scope of its research programs and/or limit or cease its operations. The Company believes that its existing cash, cash equivalents and investments as of December 31, 2018 will provide sufficient funds to enable it to meet its obligations for at least the next 12 months from the issuance of the Company’s financial statements as of and for the 12 months ended December 31, 2018.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Significant Accounting Policies	2. Significant Accounting Policies Basis of Presentation These financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented. Reverse Stock Split On January 8, 2018, the Company effected a reverse split of shares of the Company’s common stock at a ratio of 1-for-2.6975 pursuant to an amendment to the amended and restated certificate of incorporation approved by the Company’s board of directors and stockholders. The par value and the authorized shares of the common stock were not adjusted as a result of the reverse split. All issued and outstanding common stock share and per share amounts contained in the financial statements have been retroactively adjusted to reflect this reverse split for all periods presented, and the conversion ratio of the preferred stock was adjusted accordingly. Segments The Company operates in one segment. Management uses one measurement of profitability and does not segregate its business for internal reporting. All long‑lived assets are maintained in the United States of America. Use of Estimates Preparation of financial statements in conformity with U.S. GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting periods covered by the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, stock‑based compensation expense, the resolution of uncertain tax positions and valuation allowance, recovery of long‑lived assets and accruals for research and development costs. Management bases its estimates on historical experience on various assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ materially from those estimates. Risk and Uncertainties The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential drug candidate, uncertainty of market acceptance of the Company’s product candidate, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers. The Company’s product candidate requires clearances from the U.S. Food and Drug Administration (“FDA”) or other international regulatory agencies prior to commercial sales. There can be no assurance that the product candidate will receive the necessary clearances. If the Company was denied clearance, clearance was delayed or the Company was unable to maintain clearance, it could have a materially adverse impact on the Company. The Company expects to incur substantial operating losses for the next several years and will need to obtain additional financing in order to complete clinical studies and launch and commercialize any product candidates for which it receives regulatory approval. There can be no assurance that such financing will be available or will be at terms acceptable by the Company. Cash and Cash Equivalents Cash and cash equivalents are stated at fair value. Cash equivalents include only securities having an original maturity of three months or less at the time of purchase. The Company limits its credit risk associated with cash and cash equivalents by placing its investments with an institution it believes is highly creditworthy and with highly rated money market funds. As of December 31, 2018 and 2017, cash and cash equivalents consisted of bank deposits, cash and investments in money market funds. Investment Securities The Company classifies its investment securities as available‑for‑sale. Those investments with maturities less than 12 months at the date of purchase are considered short‑term investments. Those investments with maturities greater than 12 months at the date of purchase are considered long‑term investments. The Company’s investment securities classified as available‑for‑sale are recorded at fair value based upon quoted market prices at period end. Unrealized gains and losses, deemed temporary in nature, are reported as a separate component of comprehensive income or loss. A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. Premiums (discounts) are amortized (accreted) over the life of the related security as an adjustment to yield using the straight‑line interest method. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold. Property and Equipment, Net Property and equipment are stated at cost and depreciated using the straight‑line method over the estimated useful lives of the assets, generally between three and five years. Maintenance and repairs are charged to expense as incurred, and improvements are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in operations in the period realized. Fair Value of Financial Instruments The carrying amounts of the Company’s financial instruments, which include cash, accounts payable and accrued liabilities and other current liabilities, and deferred revenue approximate their fair values due to their short maturities. Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist principally of cash, cash equivalents and investments. As of December 31, 2018 and 2017, the majority of our cash, cash equivalents and investments are held by two U.S. financial institutions in excess of federally insured limits. We invest cash in excess of our current needs in United States Treasury and government agency securities, highly‑rated short or medium‑term debt securities and money market funds and, by policy, diversify our investments to limit the amount of credit exposure. The Company has an investment policy which limits the Company to investing in highly rated corporate and government notes, and no individual investment may comprise more than 5% of the total portfolio except for securities issued by the U.S. Treasury, U.S. government agencies and money market funds, which are exempt from this restriction. Income Taxes The Company accounts for income taxes under the asset and liability method which requires, among other things, that deferred income taxes be provided for temporary differences between the tax basis of the Company’s assets and liabilities and their financial statement reported amounts. Management makes estimates, assumptions and judgments to determine the Company’s provision for income taxes and also for deferred tax assets and liabilities, and any valuation allowances recorded against the Company’s deferred tax assets. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and to the extent the Company believes that recovery is not more likely than not, the Company must establish a valuation allowance. The Company has adopted ASC 740-10, Accounting for Uncertainty in Income Taxes, that prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of uncertain tax positions taken or expected to be taken in the Company’s income tax return, and also provides guidance on derecognition, classification, interest and penalties, accounting in interim periods, disclosure and transition. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits. Research and Development Expenses Research and development costs are expensed as incurred. Substantially all of our research and development expenses consist of expenses incurred in connection with the development of serlopitant. These expenses include certain payroll and personnel expenses including stock‑based compensation expense, consulting costs, contract manufacturing costs, and fees paid to clinical research organizations, or CROs, to conduct research and development. Nonrefundable advance payments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized and recognized as an expense as the goods are delivered or the related services are performed. The Company estimates non‑clinical study and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage non‑clinical studies and clinical trials on its behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the receipt of the related services are recorded as prepaid expenses until the services are rendered. Stock-Based Compensation The Company measures and recognizes compensation expense for all stock‑based awards made to employees, directors and non‑employees, based on estimated fair values recognized using the straight‑line method over the requisite service period and is reduced for forfeitures as they occur. The fair value of options to purchase common stock granted to employees is estimated on the grant date using the Black‑Scholes option valuation model. The calculation of stock‑based compensation expense requires that the Company make certain assumptions and judgments about a number of complex and subjective variables used in the Black‑Scholes model, including the expected term, expected volatility of the underlying common stock, risk‑free interest rate. The Company accounts for options issued to non‑employees using the Black‑Scholes option valuation model and is measured and recognized as the stock options are earned. Convertible Preferred Stock The Company recorded convertible preferred stock at fair value on the dates of issuance, net of issuance costs. The convertible preferred stock is recorded outside of stockholders’ equity (deficit) because, in the event of certain deemed liquidation events considered not solely within the Company’s control, such as a merger, acquisition and sale of all or substantially all of the Company’s assets, the convertible preferred stock will become redeemable at the option of the holders. All outstanding convertible preferred stock converted into common stock in January 2018 upon the effectiveness of the IPO. Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity of the Company during a period from transactions and other events and circumstances excluding transactions resulting from investments and distributions to owners. Comprehensive loss consists of the net loss and changes in accumulated other comprehensive income, which are comprised of unrealized gains (losses) on available‑for‑sale investments. Revenue Recognition The Company records revenue based on a five-step model in accordance with Accounting Standards Codification ("ASC") 606, Revenue from Contracts with Customers ("ASC 606"). For the Company’s collaboration agreement, which is discussed further under Note 5, the Company identifies the performance obligations, determines the transaction price, allocates the contract transaction price to the performance obligations, and recognizes the revenue when (or as) the performance obligation is satisfied. The Company identifies the performance obligations included within the agreement and evaluates which performance obligations are distinct. Upfront payments for licenses are evaluated to determine if the license is capable of being distinct from the obligations of the Company to participate on certain development and/or commercialization committees with the collaboration partners and supply manufactured drug product for clinical trials. For performance obligations that the Company satisfies over time, the Company utilizes the input method and revenue is recognized by consistently applying a method of measuring progress toward complete satisfaction of that performance obligation. The Company periodically reviews its estimated periods of performance based on the progress under each arrangement and accounts for the impact of any changes in estimated periods of performance on a prospective basis. Milestone payments are a form of variable consideration as the payments are contingent upon achievement of a substantive event. Milestone payments are estimated and included in the transaction price when the Company determines that it is probable that there will not be a significant reversal of cumulative revenue recognized in future periods. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such milestones and any related constraint, and if necessary, adjusts the estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration or other revenues and earnings in the period of adjustment. Research and development revenues and cost reimbursements are based upon negotiated rates for the Company’s full-time employee equivalents (“FTE”) and actual out-of-pocket costs. FTE rates are set based upon the Company’s costs, and which the Company believes approximate fair value. None of the revenues recognized to date are refundable if the relevant research effort is not successful. In accordance with ASC 606, the Company is required to adjust the transaction price for the effects of the time value of money if the timing of payments agreed to by the parties to the contract, explicitly or implicitly, provides the Company or its customer with a significant benefit of financing the transfer of goods or services. The Company concluded that its collaboration agreement did not contain a significant financing component because the payment structure of its agreements arise from reasons other than providing a significant benefit of financing. Net Loss per Share of Common Stock Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted‑average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted‑average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, convertible preferred stock and common stock options are considered to be potentially dilutive securities. Because the Company has reported a net loss for the years ended December 31, 2018, 2017 and 2016, diluted net loss per common share is the same as basic net loss per common share for those periods. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014‑09, Revenue from Contracts with Customers (Topic 606) Revenue Recognition Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date In February 2016, the FASB issued ASU 2016‑02, Leases Targeted Improvements to ASC 842 In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses — Measurement of Credit Losses on Financial Instruments In February 2018, the FASB issued ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In June 2018, the FASB issued ASU 2018-07 Improvements to Nonemployee Share-Based Payment Accounting (Topic 718) In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532, Disclosure Update and Simplification In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820)

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The fair value of our financial instruments reflects the amounts that we estimate we would receive in connection with the sale of an asset or pay in connection with the transfer of a liability in an orderly transaction between market participants at the measurement date (exit price). We disclose and recognize the fair value of our assets and liabilities using a hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to valuations based upon unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to valuations based upon unobservable inputs that are significant to the valuation (Level 3 measurements). The guidance establishes three levels of the fair value hierarchy as follows: Level 1 ‑ Inputs that reflect unadjusted quoted prices in active markets for identical assets or liabilities that we have the ability to access at the measurement date; Level 2 ‑ Inputs other than quoted prices that are observable for the assets or liability either directly or indirectly, including inputs in markets that are not considered to be active; Level 3 ‑ Inputs that are unobservable. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. The Company recognizes transfers between levels of the fair value hierarchy as of the end of the reporting period. There were no transfers within the hierarchy during the years ended December 31, 2018 and 2017. A summary of the assets and liabilities carried at fair value in accordance with the hierarchy defined above is as follows (in thousands): Fair Value Measurements Using Level 1 Level 2 Level 3 Total December 31, 2018 Assets: Money market funds $ 5,802 $ — $ — $ 5,802 Corporate notes — 41,035 — 41,035 Commercial paper — 63,036 — 63,036 Asset backed securities — 12,213 — 12,213 Government notes — 12,476 — 12,476 Total assets $ 5,802 $ 128,760 $ — $ 134,562 Fair Value Measurements Using Level 1 Level 2 Level 3 Total December 31, 2017 Assets: Money market funds $ 8,685 $ — $ — $ 8,685 Corporate notes 5,103 40,995 — 46,098 Government notes 6,175 — — 6,175 Total assets $ 19,963 $ 40,995 $ — $ 60,958 The Company uses a market approach for determining the fair value of all its Level 1 and Level 2 money market funds and marketable securities. To value its money market funds, the Company values the funds at $1 stable net asset value, which is the market pricing convention for identical assets that the Company has the ability to access. The investments are classified as available‑for‑sale securities. At December 31, 2018 and 2017, the balance in the Company’s accumulated other comprehensive income was comprised solely of activity related to the Company’s available‑for‑sale securities. There were no realized gains or losses recognized on the sale or maturity of available‑for‑sale securities for the years ended December 31, 2018 and 2017 and as a result, the Company did not reclassify any amounts out of accumulated other comprehensive income for the year. The Company has a limited number of available‑for‑sale securities in insignificant loss positions as of December 31, 2018 and 2017, which the Company does not intend to sell and has concluded it will not be required to sell before recovery of the amortized cost for the investment at maturity. The following table summarizes the available‑for‑sale securities (in thousands): Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2018 Money market funds $ 5,802 $ — $ — $ 5,802 Corporate notes 41,103 2 (70 ) 41,035 Commercial paper 63,036 — — 63,036 Asset backed securities 12,236 — (23 ) 12,213 Government notes 12,481 — (5 ) 12,476 $ 134,658 $ 2 $ (98 ) $ 134,562 Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2017 Money market funds $ 8,685 $ — $ — $ 8,685 Corporate notes 46,133 — (35 ) 46,098 Government notes 6,191 — (16 ) 6,175 $ 61,009 $ — $ (51 ) $ 60,958

Balance Sheets Components

Balance Sheets Components	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheets Components	4. Balance Sheets Components Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2018 2017 Accrued personnel expenses $ 2,649 $ 1,108 Accrued clinical and development expenses 3,349 2,250 Other 256 201 Total $ 6,254 $ 3,559

License Agreements

License Agreements	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License Agreements	5. License Agreements In December 2012, the Company entered into an exclusive worldwide royalty free license agreement with Merck Sharp & Dohme Corp., or “Merck” for exclusive worldwide rights for the development and commercialization of serlopitant and two other NK 1 In May 2018, the Company paid a $3.0 million milestone payment associated with the initiation of the Company’s Phase 3 clinical program for pruritus associated with prurigo nodularis. Future milestone payments are considered a form of variable consideration and accrued for when the Company determines that it is probable that there will not be a significant reversal of the accrual in future periods. JT Torii Collaboration Agreement In August 2016, the Company entered into a license and collaboration agreement (the “Collaboration Agreement”) with Japan Tobacco Inc. and Torii Pharmaceutical Co. Ltd. (together referred to as “JT Torii”). Under the Collaboration Agreement, the Company granted to JT Torii the rights to develop and commercialize products containing serlopitant in Japan, for the treatment of diseases and conditions other than nausea or vomiting. In exchange, JT Torii paid the Company an upfront, non‑refundable payment of $11.0 million. In addition, the Company was entitled to receive aggregate payments of up to $28.0 million upon the achievement of specified development and regulatory milestones, and $15.0 million upon the achievement of a commercial milestone, as well as tiered royalties from the mid-single digits up to the mid‑teens on sales of licensed products in Japan. The Company’s performance obligations under the license agreement included the transfer of intellectual property rights in the form of licenses, obligations to participate on certain development and/or commercialization committees with the collaboration partners and supply manufactured drug product for clinical trials. In the second quarter of 2018, the Company and JT Torii agreed to terminate the Collaboration Agreement and JT Torii halted development activities in Japan. As a result, the Company has reacquired full ownership of the development and commercialization rights to serlopitant in Japan and accelerated recognition of the remaining deferred revenue of $8.1 million during the quarter. In the second quarter of 2018, the Company also earned and recognized a $2.0 million milestone payment related to JT Torii’s receipt of investigational new drug application (“IND”) enabling past clinical study reports delivered by the Company under the Collaboration Agreement. Under the Collaboration Agreement, the Company was reimbursed by JT Torii for the non-commercial supplies of serlopitant at the same rate it was charged by the third-party manufacturer for such supplies, which price did not include a significant or incremental discount for JT Torii. The assessment of performance obligations required judgment in order to determine the allocation of revenue to each deliverable and the appropriate period of time over which the revenue should be recognized. Under the Collaboration Agreement, the Company determined that the license was not distinct from the research and development services because JT Torii could not use the license with its available resources to obtain any economic value without the Company’s participation. The license and the services were combined as one unit of accounting and upfront payments were recorded initially as deferred revenue in the balance sheet. Revenue was then recognized over an estimated performance period as performance of services was being completed. The Company recognized the upfront fee based on performance of the obligation using input method over the period of performance, which represented the estimated development period in the territories based on the initial development plan managed by the joint steering committee. The original term of the agreement was through the expiration of the patents associated with serlopitant. Under the Collaboration Agreement, two of the milestones, which amount to $2.0 million each, related to the preparation of an IND for submission to regulatory authorities in the territory were considered substantive given that they are triggered by the Company’s performance relative to the achievement of pre-specified, “at risk” milestone events, including the submission of all completed trials clinical data packages and the validation of the manufacturing process. The Company earned and recognized a $2.0 million milestone payment during each of the years ended December 31, 2018 and 2017. On September 1, 2017, the Company entered into a new services agreement with JT Torii to provide research and development services, including regulatory, chemistry and manufacturing support and related materials that is distinct from the original Collaboration Agreement. The Company evaluated the new services agreement and determined that the research and materials delivered to JT Torii represented another contract that provides distinct goods and services to JT Torii. The fees received under the services agreement were recognized as and when such services were performed by the Company and JT Torii consumed the benefits of those services. During the years ended December 31, 2018, 2017, and 2016, the Company recognized revenue of $10.6, $4.6, and $0.7 million respectively in the statement of operations related to the services agreement and Collaboration Agreement. The services agreement terminated upon the termination of the Collaboration Agreement.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Legal Matters The Company’s industry is characterized by frequent claims and litigation, including claims regarding intellectual property. As a result, the Company may be subject to various legal proceedings from time to time. The results of any future litigation cannot be predicted with certainty, and regardless of the outcome, litigation can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources and other factors. On November 8, 2018, a putative securities class action complaint captioned Pavel Savelstrov v. Menlo Therapeutics, Inc., et al., Case No.18-CIV-06049, was filed in state court in the Superior Court of the State of California, County of San Mateo, against the Company, certain of its current executive officers and its directors, and certain underwriters in the Company’s initial public offering. On January 28, 2019, a putative securities class action complaint captioned Hugh McKay v. Menlo Therapeutics, Inc., et al. , was filed in state court in the Superior Court of the State of California, County of San Mateo, against the Company, certain of its current executive officers and its directors, and certain underwriters in the Company’s initial public offering. The complaints allege violations of Sections 11, 12(a)(2) and 15 of the Securities Act of 1933 due to allegedly false and misleading statements in connection with the Company’s initial public offering. The Company believes that the lawsuits are without merit and intends to vigorously defend itself. Accordingly, the Company cannot reasonably estimate any range of potential future charges, and the Company has not recorded any accrual for a contingent liability associated with these legal proceeding. Leases The Company conducts its operations using leased office facilities. In September 2017, the Company entered into a lease agreement. The 30 month lease, beginning on October 1, 2017, provides approximately 14,000 square feet of office space in Redwood City, California. Base annual rent is approximately $55,000 per month, with annual increases. The Company recognizes rent expense on a straight‑line basis over the respective lease period. Rent expense for the years ended December 31, 2018, 2017 and 2016 was $0.8 million, $0.4 million and $0.2 million, respectively. As of December 31, 2018, total future minimum lease payments under our operating leases are as follows (in thousands): Year ending December 31: 2019 $ 675 2020 173 Total future minimum lease payments $ 848 Indemnification As permitted under Delaware law and in accordance with the Company’s bylaws, the Company is required to indemnify its officers and directors for certain events or occurrences while the officer or director is or was serving in such capacity. The Company is also party to indemnification agreements with its directors. The Company believes the fair value of the indemnification rights and agreements is minimal. Accordingly, the Company has not recorded any liabilities for these indemnification rights and agreements as of December 31, 2018. Contingencies From time to time, we may have certain contingent liabilities that arise in the ordinary course of our business activities. We accrue a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Convertible Preferred Stock	7 . Convertible Preferred Stock As of December 31, 2017, the Company’s Certificate of Incorporation, as amended, authorized the Company to issue up to 28,322,761 shares of convertible preferred stock, par value of $0.001, of which 14,300 were designated Series A convertible preferred stock and 14,106,583 are designated Series B convertible preferred stock, and 14,201,878 shares are designated Series C convertible preferred stock. In July 2017, the Company issued 11,854,463 shares of Series C convertible preferred stock to investors at $4.26 per share with gross proceeds of $50.5 million. In January 2018, the Company completed its initial public offering (“IPO”) of shares of its common stock, pursuant to which the Company issued 8,050,000 shares of common stock, which includes 1,050,000 shares issued pursuant to the over-allotment option granted to its underwriters and received net proceeds of approximately $125.4 million, after deducting underwriting discounts, commissions and offering expenses. In connection with the completion of the Company's IPO, all shares of convertible preferred stock converted into 9,629,405 shares of common stock. As of December 31, 2018, the Company had no outstanding convertible preferred stock. Liquidation Preference In the event of any liquidation, dissolution, or winding up of the Company, either voluntary or involuntary, the holders of the then outstanding shares of Series A convertible stock and Series B convertible preferred stock and Series C convertible preferred stock were first entitled to receive the amount of $1,000 and $3.19 and $4.26 per share, respectively plus all declared but unpaid dividends for such shares, prior and in preference to any distribution of any assets of the Company to the holders of the common stock. Upon the occurrence of such event, the proceeds distributed among the holders of the Series A, B and C convertible preferred stock were insufficient to permit the full payment of the aforesaid preferential amounts to each holder the convertible preferred stock, then the entire proceeds legally available for distribution to the convertible preferred stock were to be distributed ratably among the holders of the Series A, B and C convertible preferred stock in proportion to the full preferential amount that each such holder of convertible preferred stock is otherwise entitled to receive. Upon completion of the distributions required by the above‑mentioned liquidation preferences, any remaining proceeds were to be distributed among the holders of Series B and C convertible preferred stock and common stock pro rata based on the number of shares of common stock held by each, assuming full conversion of the Series B and C convertible preferred stock to common stock at the then‑effective conversion price for such shares. Dividends The holders of shares of Series A, B and C convertible preferred stock were entitled to receive non‑cumulative dividends, out of any assets legally available, prior and in preference to any declaration or payment of any dividend on the common stock, at the applicable dividend rate of $80.00 per annum for each share of Series A convertible preferred stock, $0.2552 per annum for each share of Series B convertible preferred stock and $0.3408 per share per annum for each share of Series C convertible preferred stock, all subject to adjustment from time to time for recapitalizations, payable when and if declared by the Company’s board of directors. The Company has never declared any dividends on its convertible preferred stock. Voting The holder of each share of Series B and C convertible preferred stock were entitled to one vote for each share of common stock into which such preferred stock could then be converted and, with respect to such vote, such holder has full voting rights and powers equal to the voting rights and powers of the holders of common stock and was entitled to notice of any stockholders’ meeting in accordance with the Company’s bylaws. The holders of shares of Series A convertible preferred stock did not have a right to vote, other than as required by Delaware law and for certain directors, as set forth below. The holders of shares of Series A convertible preferred stock were entitled to elect two of the Company’s directors. The holders of Series B convertible preferred stock were entitled to elect two of the Company’s directors. The holders of Series C convertible preferred stock were entitled to elect one of the Company’s directors. The holders of outstanding common stock were entitled to elect three of the Company’s directors. The holders of convertible preferred stock and common stock, voting together as a single class, and not as separate series, and on an as converted basis, were entitled to elect any remaining directors of the Company, subject to the approval of the then serving members of the Company’s directors. Conversion The holder of each share of convertible preferred stock had the option to convert each share of convertible preferred stock into such number of fully paid and nonassessable shares of common stock as is determined by dividing the applicable original issue price for such series by the applicable conversion price for such series in effect on the date the certificate is surrendered for conversion. Each share of convertible preferred stock automatically converted into shares of common stock at the conversion rate at the time in effect for such series of convertible preferred stock immediately pursuant to a registration statement under the Securities Act of 1933, with gross proceeds of not less than $40.0 million in the aggregate and an offering price to the public of no less than $17.21 per share. The conversion price of the convertible preferred stock was initially set at an amount equal to the issue price. The Series B and C convertible preferred stock conversion price was subject to adjustment for stock dividends, stock splits, re‑capitalization and upon the occurrence of certain triggering events related to anti‑dilution protection rights. In the event that a future preferred stock financing should occur at a price lower than the last preferred financing round, the conversion ratios of the existing preferred stock are changed to protect the ownership position of existing investors.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Common Stock	8 . Common Stock As of December 31, 2018, the Company’s Certificate of Incorporation, as amended, authorizes the Company to issue 300,000,000 shares of $0.0001 par value common stock. Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when and if declared by the board of directors, subject to the prior rights of holders of all classes of preferred stock outstanding. The Company has never declared any dividends on common stock.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	9 . Stock-Based Compensation Under the Company’s 2011 Stock Incentive Plan (the “2011 Plan”), the Company may grant options to purchase common stock, restricted stock awards, or directly issue shares of common stock to employees, directors and consultants of the Company. Under the 2011 Plan, options granted are exercisable over a maximum term of 10 years from the date of grant and generally vest over a period of four years. The Company adopted a 2018 Omnibus Incentive Plan (the “2018 Plan”), effective January 2018. The 2018 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock, restricted stock units, dividend equivalent rights and other stock and cash-based awards (including annual cash incentives and long-term cash incentives). The Company has reserved 3,000,000 shares of common stock for issuance pursuant to awards under the 2018 Plan. As of December 31, 2018, the Company has 1,319,109 shares of common stock available for issuance under the 2018 Plan. The Company adopted a 2018 Employee Stock Purchase Plan, or ESPP in January 2018. The ESPP enables eligible employees of the Company and designated affiliates to purchase shares of common stock at a discount of 15%. Six month offer periods under the ESPP commenced on September 1, 2018. The Company has reserved 325,000 shares of common stock for issuance under the ESPP. Total stock‑based compensation expense for employees and non‑employees recognized in the statements of operations was as follows (in thousands): Year Ended December 31, 2018 2017 2016 Research and development $ 1,734 $ 792 $ 257 General and administrative 1,904 660 316 Total stock-based compensation expense $ 3,638 $ 1,452 $ 573 In connection with services rendered by non-employees, the Company recorded stock-based compensation expense of $0.5 million, $0.6 million, and $0.3 million in 2018, 2017 and 2016, respectively. At December 31, 2018, there was approximately $11.9 million of unamortized compensation expense, which was expected to be recognized over a weighted average period of 3.0 years. 2011 and 2018 Plan The table below summarizes stock option and restricted award activity under the 2011 Plan and 2018 Plan: Number of Shares Outstanding Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Balances at January 1, 2016 — Granted 1,485,132 $ 1.99 Balances at December 31, 2016 1,485,132 1.99 9.32 $ 3,805 Granted 1,040,329 5.56 Exercised (1) (18,535 ) 1.83 Balances at December 31, 2017 2,506,926 3.50 8.79 $ 24,033 Granted 1,700,013 7.58 Exercised (1) (255,186 ) 1.94 Forfeited/expired (46,283 ) 5.94 Balances at December 31, 2018 3,905,470 $ 5.35 8.65 $ 2,509 (1) Includes early exercise of 317,405 options during the year ended December 31, 2016, of which 59,513 and 139,636 remain unvested as of December 31, 2018 and December 31, 2017, respectively. Upon vesting of restricted shares and exercise of options, the Company issues common stock from its authorized shares. During the years ended December 31, 2018, 2017 and 2016, the Company received $496,000, $34,000 and zero upon the exercise of stock options, respectively. As of December 31, 2018 and 2017, the Company had recorded a liability of $18,000 and $43,000, respectively for the early exercise of stock options, recorded as other current liabilities and other non‑current liabilities. When options are subject to the Company’s repurchase right, the Company may buy back any unvested shares at their original exercise price in the event of an employee’s termination prior to full vesting. The aggregate grant date fair value of employee options vesting during the years ended December 31, 2018, 2017 and 2016 was approximately $2.6 million, $0.5 million and $0.2 million, respectively. The aggregate intrinsic value of shares exercised during the years ended December 31, 2018, 2017 and December 31, 2016 was $1.8 million, $0.2 million and zero, respectively. The weighted average grant date fair value of stock options granted was $5.00, $5.56 and $1.79 per share during the years ended December 31, 2018, 2017, and 2016, respectively. Stock Awards Granted to Employees and Directors Stock‑based compensation expense is based on the grant date fair value. The Company recognizes compensation expense for all stock‑based options and restricted awards on a straight‑line basis over the requisite service period of the awards, which is generally the option vesting term of four years. The fair value of each option award is estimated on the date of grant using the Black-Scholes option valuation model. The Company determines the price volatility based on the historical volatilities of industry peers as it has no trading history for its common stock price. Industry peers consist of several public companies in the biotechnology industry with comparable characteristics, including clinical trials progress and therapeutic indications. The expected term of the options is based on the average period the stock options are expected to remain outstanding. As the Company does not have sufficient historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior, the expected term is calculated as the midpoint between the weighted-average vesting term and the contractual expiration period also known as the simplified method. The risk-free rate is based on U.S. Treasury zero coupon issues with remaining terms consistent with the expected terms of the stock options, as determined at the time of grant. To date, the Company has not declared or paid any cash dividends and does not have any plans to do so in the future. Therefore, the Company used an expected divided yield of zero. The following assumptions were used to calculate the fair value of awards granted to employees and directors during the years indicated: Year Ended December 31, 2018 2017 2016 Expected term (in years) 6.0 - 6.1 6.0 - 6.1 4.6 - 6.1 Volatility 72% - 73% 75% - 100% 68% - 74% Risk-free interest rate 2.8% - 3.0% 1.9% - 2.3% 1.3% - 2.1% Dividend yield — — — Stock-Based Compensation for Non-employees Stock‑based compensation expense related to stock awards granted to non‑employees is recognized as the awards vest. The Company believes that the fair value of the stock‑based awards granted is more reliably measurable than the fair value of the services received. The fair value of stock awards granted is calculated using the Black‑Scholes option valuation model. The fair values of common stock awards granted to non‑employees were calculated using the following assumptions for the periods presented: Year Ended December 31, 2018 2017 2016 Expected term (in years) 7.3 - 10 8.3 - 10 9.3 - 10.0 Volatility 68% - 79% 74% - 100% 84% - 86% Risk-free interest rate 2.8% - 3.0% 2.1% - 2.5% 1.6% - 2.5% Dividend yield — — — Employee Stock Purchase Plans The fair value of each ESPP award is estimated on the first day of the offering period using the Black-Scholes option pricing model and is recognized in expense over the service period using the straight-line method. The key input assumptions used to estimate fair value of these awards include the exercise price of the award of $7.78, the expected option term of 0.5 years, the expected volatility of the Company’s stock over the option’s expected term of 2.13%, the risk-free interest rate over the option’s expected term of 2.27%, and the Company’s expected dividend yield at zero.

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders	10 . Net Loss per Share Attributable to Common Stockholders The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2018 2017 2016 Numerator: Net loss attributable to common stockholders, basic and diluted $ (51,445 ) $ (29,076 ) $ (14,068 ) Denominator: Weighted-average common shares outstanding 21,764,636 5,285,542 5,280,058 Less: weighted-average common shares subject to repurchase (95,947 ) (177,421 ) (292,925 ) Weighted-average common shares used to compute basic and diluted net loss per share 21,668,689 5,108,121 4,987,133 Net loss per share attributable to common stockholders: Basic and diluted $ (2.37 ) $ (5.69 ) $ (2.82 ) The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive: December 31, 2018 2017 2016 Stock options outstanding 3,905,470 2,506,926 1,485,132 Outstanding common stock subject to repurchase 59,513 139,636 222,077 Shares issuable related to ESPP 59,735 — — Convertible preferred stock issuable upon conversion to common stock — 9,629,405 5,234,800 Total 4,024,718 12,275,967 6,942,009

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	11 . Income Taxes The Company did not record a provision or benefit for income taxes during the years ended December 31, 2018, 2017 and 2016. The tax effect of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets are as follows (in thousands): Year Ended December 31, 2018 2017 2016 Deferred Tax Assets NOLs $ 22,248 $ 10,404 $ 10,458 Depreciation and Amortization 241 226 328 Stock-Based Compensation 627 274 161 Research & Development Credits 3,972 2,063 586 Deferred Revenue — 1,791 — Other Accruals 507 235 98 Total Deferred Tax Assets $ 27,595 $ 14,993 $ 11,631 Valuation Allowance (27,595 ) (14,993 ) (11,631 ) Net Deferred Tax Assets $ — $ — $ — Realization of deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance. The net change in the total valuation allowance for the years ended December 31, 2018, 2017 and 2016 was an increase of approximately $12.6 million, $3.4 million, and $5.0 million, respectively. As of December 31, 2018 and 2017, the Company had net operating loss carryforwards for federal income tax purposes of $100.6 million and $44.3 million, respectively which expire beginning in the year 2031 and federal research and development tax credits of $4.1 million and $2.1 million, respectively which expire beginning in the year 2031. As of December 31, 2018 and 2017, the Company had net operating loss carryforwards for state income tax purposes of $16.8 million and $15.0 million, respectively which expire beginning in the year 2031 and state research and development tax credits of $1.4 million and $0.9 million, respectively which do not expire. Federal and state tax laws impose substantial restrictions on the utilization of the net operating loss and credit carryforwards in the event of an ownership change as defined in Section 382 of the Internal Revenue Code. Accordingly, the Company’s ability to utilize these carryforwards may be limited as a result of such ownership change. Such a limitation could result in the expiration of carryforwards before they are utilized. The Company has adopted ASC 740-10, Accounting for Uncertainty in Income Taxes The Company recognizes interest and penalties related to uncertain tax positions in income tax expense. To the extent accrued interest and penalties do not ultimately become payable, amounts accrued will be reduced and reflected as a reduction of the provision for income taxes in the period that such determination is made. As of December 31, 2018 the Company had no accrued interest and penalties related to uncertain tax positions. The Company filed US and California tax returns with varying statues of limitations. The federal and California tax years from 2011 to 2017 remain open to examination due to the carryover of unused net operating losses and tax credits. The Company does not expect any material changes to the estimated amount of liability associated with its uncertain tax positions within the next 12 months. Uncertain Tax Positions The following table summarizes the activity related to unrecognized tax benefits (in thousands): For the year ended December 31, 2018 2017 2016 Tax Benefits: Unrecognized Benefit beginning of period $ 803 $ 229 $ 93 Gross Increases - prior period tax positions — 59 — Gross Increases - current period tax positions 652 515 136 Total Unrecognized Benefit - end of period $ 1,455 $ 803 $ 229 Tax Reform On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 34% to 21% (the “Rate Reduction”) effective for tax years beginning after December 31, 2017. The Company reduced deferred tax assets at December 31, 2017 for the effect of the Rate Reduction. The Rate Reduction did not impact the Company's provision for income taxes for 2017 due to the full valuation allowance on deferred tax assets. Staff Accounting Bulletin No. 118 ("SAB 118") was issued to address the application of US GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. The Company determined that $7.0 million of the reduction in deferred tax assets resulting from Rate Reduction was both provisional and a reasonable estimate at December 31, 2017. Additionally, the Company is still in the process of analyzing certain provisions of the Act including the application of new executive compensation limitation provisions under Internal Revenue Section 162(m). These items are subject to revisions from further analysis of the Tax Act and interpretation of any additional guidance issued by the U.S. Treasury Department, IRS, FASB, and other standard-setting and regulatory bodies.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	12 . Related Party Transactions From 2011 through 2016, the Company has operated with significant consulting and management services provided by Velocity Pharmaceutical Development, LLC (“VPD”). Development services fees paid to VPD under the Development Services Agreement was $1.0 million for the year ended December 31, 2016. The Company also reimbursed VPD for consulting, travel and other expenses incurred on our behalf. As of December 31, 2018 and 2017, the Company did not have any outstanding liabilities or fees to VPD. Several managing directors of VPD have served as officers and directors of the Company. David Collier, M.D., a former member of the Company’s board of directors, is the Chief Executive Officer of VPD, and Xiaoming Zhang, Ph.D., our Senior Vice President, Non‑Clinical and Pharmaceutical Development, is a Venture Partner of VPD.

Selected Unaudited Quarterly Fi

Selected Unaudited Quarterly Financial Data	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Unaudited Quarterly Financial Data	13. The following tables show a summary of the Company’s unaudited quarterly financial data for each of the four quarters of 2018 and 2017 (in thousands, except per share amounts): Three Months Ended December 31, 2018 September 30, 2018 June 30, 2018 March 31, 2018 Collaboration and service revenue $ — $ — $ 10,143 $ 497 Operating expenses 18,440 13,702 19,316 13,717 Other income (expense), net 846 855 826 563 Net loss (17,594 ) (12,847 ) (8,347 ) (12,657 ) Basic and diluted net loss per common share (1) $ (0.76 ) $ (0.56 ) $ (0.36 ) $ (0.72 ) Three Months Ended December 31, 2017 September 30, 2017 June 30, 2017 March 31, 2017 Collaboration and service revenue $ 2,775 $ 909 $ 449 $ 449 Operating expenses 12,252 9,244 6,674 6,004 Other income (expense), net 200 163 72 81 Net loss (9,277 ) (8,172 ) (6,153 ) (5,474 ) Basic and diluted net loss per common share (1) $ (1.80 ) $ (1.59 ) $ (1.21 ) $ (1.08 ) (1) Basic and diluted net loss per common share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted net loss per common share.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented.
Reverse Stock Split	Reverse Stock Split On January 8, 2018, the Company effected a reverse split of shares of the Company’s common stock at a ratio of 1-for-2.6975 pursuant to an amendment to the amended and restated certificate of incorporation approved by the Company’s board of directors and stockholders. The par value and the authorized shares of the common stock were not adjusted as a result of the reverse split. All issued and outstanding common stock share and per share amounts contained in the financial statements have been retroactively adjusted to reflect this reverse split for all periods presented, and the conversion ratio of the preferred stock was adjusted accordingly.
Segments	Segments The Company operates in one segment. Management uses one measurement of profitability and does not segregate its business for internal reporting. All long‑lived assets are maintained in the United States of America.
Use of Estimates	Use of Estimates Preparation of financial statements in conformity with U.S. GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting periods covered by the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, stock‑based compensation expense, the resolution of uncertain tax positions and valuation allowance, recovery of long‑lived assets and accruals for research and development costs. Management bases its estimates on historical experience on various assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ materially from those estimates.
Risk and Uncertainties	Risk and Uncertainties The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential drug candidate, uncertainty of market acceptance of the Company’s product candidate, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers. The Company’s product candidate requires clearances from the U.S. Food and Drug Administration (“FDA”) or other international regulatory agencies prior to commercial sales. There can be no assurance that the product candidate will receive the necessary clearances. If the Company was denied clearance, clearance was delayed or the Company was unable to maintain clearance, it could have a materially adverse impact on the Company. The Company expects to incur substantial operating losses for the next several years and will need to obtain additional financing in order to complete clinical studies and launch and commercialize any product candidates for which it receives regulatory approval. There can be no assurance that such financing will be available or will be at terms acceptable by the Company.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents are stated at fair value. Cash equivalents include only securities having an original maturity of three months or less at the time of purchase. The Company limits its credit risk associated with cash and cash equivalents by placing its investments with an institution it believes is highly creditworthy and with highly rated money market funds. As of December 31, 2018 and 2017, cash and cash equivalents consisted of bank deposits, cash and investments in money market funds.
Investment Securities	Investment Securities The Company classifies its investment securities as available‑for‑sale. Those investments with maturities less than 12 months at the date of purchase are considered short‑term investments. Those investments with maturities greater than 12 months at the date of purchase are considered long‑term investments. The Company’s investment securities classified as available‑for‑sale are recorded at fair value based upon quoted market prices at period end. Unrealized gains and losses, deemed temporary in nature, are reported as a separate component of comprehensive income or loss. A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. Premiums (discounts) are amortized (accreted) over the life of the related security as an adjustment to yield using the straight‑line interest method. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost and depreciated using the straight‑line method over the estimated useful lives of the assets, generally between three and five years. Maintenance and repairs are charged to expense as incurred, and improvements are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in operations in the period realized.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of the Company’s financial instruments, which include cash, accounts payable and accrued liabilities and other current liabilities, and deferred revenue approximate their fair values due to their short maturities.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist principally of cash, cash equivalents and investments. As of December 31, 2018 and 2017, the majority of our cash, cash equivalents and investments are held by two U.S. financial institutions in excess of federally insured limits. We invest cash in excess of our current needs in United States Treasury and government agency securities, highly‑rated short or medium‑term debt securities and money market funds and, by policy, diversify our investments to limit the amount of credit exposure. The Company has an investment policy which limits the Company to investing in highly rated corporate and government notes, and no individual investment may comprise more than 5% of the total portfolio except for securities issued by the U.S. Treasury, U.S. government agencies and money market funds, which are exempt from this restriction.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method which requires, among other things, that deferred income taxes be provided for temporary differences between the tax basis of the Company’s assets and liabilities and their financial statement reported amounts. Management makes estimates, assumptions and judgments to determine the Company’s provision for income taxes and also for deferred tax assets and liabilities, and any valuation allowances recorded against the Company’s deferred tax assets. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and to the extent the Company believes that recovery is not more likely than not, the Company must establish a valuation allowance. The Company has adopted ASC 740-10, Accounting for Uncertainty in Income Taxes, that prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of uncertain tax positions taken or expected to be taken in the Company’s income tax return, and also provides guidance on derecognition, classification, interest and penalties, accounting in interim periods, disclosure and transition. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred. Substantially all of our research and development expenses consist of expenses incurred in connection with the development of serlopitant. These expenses include certain payroll and personnel expenses including stock‑based compensation expense, consulting costs, contract manufacturing costs, and fees paid to clinical research organizations, or CROs, to conduct research and development. Nonrefundable advance payments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized and recognized as an expense as the goods are delivered or the related services are performed. The Company estimates non‑clinical study and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage non‑clinical studies and clinical trials on its behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the receipt of the related services are recorded as prepaid expenses until the services are rendered.
Stock-Based Compensation	Stock-Based Compensation The Company measures and recognizes compensation expense for all stock‑based awards made to employees, directors and non‑employees, based on estimated fair values recognized using the straight‑line method over the requisite service period and is reduced for forfeitures as they occur. The fair value of options to purchase common stock granted to employees is estimated on the grant date using the Black‑Scholes option valuation model. The calculation of stock‑based compensation expense requires that the Company make certain assumptions and judgments about a number of complex and subjective variables used in the Black‑Scholes model, including the expected term, expected volatility of the underlying common stock, risk‑free interest rate. The Company accounts for options issued to non‑employees using the Black‑Scholes option valuation model and is measured and recognized as the stock options are earned.
Convertible Preferred Stock	Convertible Preferred Stock The Company recorded convertible preferred stock at fair value on the dates of issuance, net of issuance costs. The convertible preferred stock is recorded outside of stockholders’ equity (deficit) because, in the event of certain deemed liquidation events considered not solely within the Company’s control, such as a merger, acquisition and sale of all or substantially all of the Company’s assets, the convertible preferred stock will become redeemable at the option of the holders. All outstanding convertible preferred stock converted into common stock in January 2018 upon the effectiveness of the IPO.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity of the Company during a period from transactions and other events and circumstances excluding transactions resulting from investments and distributions to owners. Comprehensive loss consists of the net loss and changes in accumulated other comprehensive income, which are comprised of unrealized gains (losses) on available‑for‑sale investments.
Revenue Recognition	Revenue Recognition The Company records revenue based on a five-step model in accordance with Accounting Standards Codification ("ASC") 606, Revenue from Contracts with Customers ("ASC 606"). For the Company’s collaboration agreement, which is discussed further under Note 5, the Company identifies the performance obligations, determines the transaction price, allocates the contract transaction price to the performance obligations, and recognizes the revenue when (or as) the performance obligation is satisfied. The Company identifies the performance obligations included within the agreement and evaluates which performance obligations are distinct. Upfront payments for licenses are evaluated to determine if the license is capable of being distinct from the obligations of the Company to participate on certain development and/or commercialization committees with the collaboration partners and supply manufactured drug product for clinical trials. For performance obligations that the Company satisfies over time, the Company utilizes the input method and revenue is recognized by consistently applying a method of measuring progress toward complete satisfaction of that performance obligation. The Company periodically reviews its estimated periods of performance based on the progress under each arrangement and accounts for the impact of any changes in estimated periods of performance on a prospective basis. Milestone payments are a form of variable consideration as the payments are contingent upon achievement of a substantive event. Milestone payments are estimated and included in the transaction price when the Company determines that it is probable that there will not be a significant reversal of cumulative revenue recognized in future periods. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such milestones and any related constraint, and if necessary, adjusts the estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration or other revenues and earnings in the period of adjustment. Research and development revenues and cost reimbursements are based upon negotiated rates for the Company’s full-time employee equivalents (“FTE”) and actual out-of-pocket costs. FTE rates are set based upon the Company’s costs, and which the Company believes approximate fair value. None of the revenues recognized to date are refundable if the relevant research effort is not successful. In accordance with ASC 606, the Company is required to adjust the transaction price for the effects of the time value of money if the timing of payments agreed to by the parties to the contract, explicitly or implicitly, provides the Company or its customer with a significant benefit of financing the transfer of goods or services. The Company concluded that its collaboration agreement did not contain a significant financing component because the payment structure of its agreements arise from reasons other than providing a significant benefit of financing.
Net Loss per Share of Common Stock	Net Loss per Share of Common Stock Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted‑average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted‑average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, convertible preferred stock and common stock options are considered to be potentially dilutive securities. Because the Company has reported a net loss for the years ended December 31, 2018, 2017 and 2016, diluted net loss per common share is the same as basic net loss per common share for those periods.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014‑09, Revenue from Contracts with Customers (Topic 606) Revenue Recognition Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date In February 2016, the FASB issued ASU 2016‑02, Leases Targeted Improvements to ASC 842 In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses — Measurement of Credit Losses on Financial Instruments In February 2018, the FASB issued ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In June 2018, the FASB issued ASU 2018-07 Improvements to Nonemployee Share-Based Payment Accounting (Topic 718) In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532, Disclosure Update and Simplification In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820)

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Summary of Assets and Liabilities Carried at Fair Value	A summary of the assets and liabilities carried at fair value in accordance with the hierarchy defined above is as follows (in thousands): Fair Value Measurements Using Level 1 Level 2 Level 3 Total December 31, 2018 Assets: Money market funds $ 5,802 $ — $ — $ 5,802 Corporate notes — 41,035 — 41,035 Commercial paper — 63,036 — 63,036 Asset backed securities — 12,213 — 12,213 Government notes — 12,476 — 12,476 Total assets $ 5,802 $ 128,760 $ — $ 134,562 Fair Value Measurements Using Level 1 Level 2 Level 3 Total December 31, 2017 Assets: Money market funds $ 8,685 $ — $ — $ 8,685 Corporate notes 5,103 40,995 — 46,098 Government notes 6,175 — — 6,175 Total assets $ 19,963 $ 40,995 $ — $ 60,958
Summary of Available-for-sale Securities	The following table summarizes the available‑for‑sale securities (in thousands): Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2018 Money market funds $ 5,802 $ — $ — $ 5,802 Corporate notes 41,103 2 (70 ) 41,035 Commercial paper 63,036 — — 63,036 Asset backed securities 12,236 — (23 ) 12,213 Government notes 12,481 — (5 ) 12,476 $ 134,658 $ 2 $ (98 ) $ 134,562 Amortized Cost Unrealized Gains Unrealized Losses Fair Value December 31, 2017 Money market funds $ 8,685 $ — $ — $ 8,685 Corporate notes 46,133 — (35 ) 46,098 Government notes 6,191 — (16 ) 6,175 $ 61,009 $ — $ (51 ) $ 60,958

Balance Sheets Components (Tabl

Balance Sheets Components (Tables)	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2018 2017 Accrued personnel expenses $ 2,649 $ 1,108 Accrued clinical and development expenses 3,349 2,250 Other 256 201 Total $ 6,254 $ 3,559

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Operating Lease Payments	As of December 31, 2018, total future minimum lease payments under our operating leases are as follows (in thousands): Year ending December 31: 2019 $ 675 2020 173 Total future minimum lease payments $ 848

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Compensation, Allocation of Recognized Period Costs	Total stock‑based compensation expense for employees and non‑employees recognized in the statements of operations was as follows (in thousands): Year Ended December 31, 2018 2017 2016 Research and development $ 1,734 $ 792 $ 257 General and administrative 1,904 660 316 Total stock-based compensation expense $ 3,638 $ 1,452 $ 573
Schedule of Stock Option and Restricted Stock Activity	The table below summarizes stock option and restricted award activity under the 2011 Plan and 2018 Plan: Number of Shares Outstanding Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Balances at January 1, 2016 — Granted 1,485,132 $ 1.99 Balances at December 31, 2016 1,485,132 1.99 9.32 $ 3,805 Granted 1,040,329 5.56 Exercised (1) (18,535 ) 1.83 Balances at December 31, 2017 2,506,926 3.50 8.79 $ 24,033 Granted 1,700,013 7.58 Exercised (1) (255,186 ) 1.94 Forfeited/expired (46,283 ) 5.94 Balances at December 31, 2018 3,905,470 $ 5.35 8.65 $ 2,509 (1) Includes early exercise of 317,405 options during the year ended December 31, 2016, of which 59,513 and 139,636 remain unvested as of December 31, 2018 and December 31, 2017, respectively.
Employees and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The following assumptions were used to calculate the fair value of awards granted to employees and directors during the years indicated: Year Ended December 31, 2018 2017 2016 Expected term (in years) 6.0 - 6.1 6.0 - 6.1 4.6 - 6.1 Volatility 72% - 73% 75% - 100% 68% - 74% Risk-free interest rate 2.8% - 3.0% 1.9% - 2.3% 1.3% - 2.1% Dividend yield — — —
Non-employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Fair Value Assumptions	The fair values of common stock awards granted to non‑employees were calculated using the following assumptions for the periods presented: Year Ended December 31, 2018 2017 2016 Expected term (in years) 7.3 - 10 8.3 - 10 9.3 - 10.0 Volatility 68% - 79% 74% - 100% 84% - 86% Risk-free interest rate 2.8% - 3.0% 2.1% - 2.5% 1.6% - 2.5% Dividend yield — — —

Net Loss per Share Attributab_2

Net Loss per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2018 2017 2016 Numerator: Net loss attributable to common stockholders, basic and diluted $ (51,445 ) $ (29,076 ) $ (14,068 ) Denominator: Weighted-average common shares outstanding 21,764,636 5,285,542 5,280,058 Less: weighted-average common shares subject to repurchase (95,947 ) (177,421 ) (292,925 ) Weighted-average common shares used to compute basic and diluted net loss per share 21,668,689 5,108,121 4,987,133 Net loss per share attributable to common stockholders: Basic and diluted $ (2.37 ) $ (5.69 ) $ (2.82 )
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive: December 31, 2018 2017 2016 Stock options outstanding 3,905,470 2,506,926 1,485,132 Outstanding common stock subject to repurchase 59,513 139,636 222,077 Shares issuable related to ESPP 59,735 — — Convertible preferred stock issuable upon conversion to common stock — 9,629,405 5,234,800 Total 4,024,718 12,275,967 6,942,009

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Deferred Tax Assets and Liabilities	The tax effect of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets are as follows (in thousands): Year Ended December 31, 2018 2017 2016 Deferred Tax Assets NOLs $ 22,248 $ 10,404 $ 10,458 Depreciation and Amortization 241 226 328 Stock-Based Compensation 627 274 161 Research & Development Credits 3,972 2,063 586 Deferred Revenue — 1,791 — Other Accruals 507 235 98 Total Deferred Tax Assets $ 27,595 $ 14,993 $ 11,631 Valuation Allowance (27,595 ) (14,993 ) (11,631 ) Net Deferred Tax Assets $ — $ — $ —
Summary of Unrecognized Tax Benefits	The following table summarizes the activity related to unrecognized tax benefits (in thousands): For the year ended December 31, 2018 2017 2016 Tax Benefits: Unrecognized Benefit beginning of period $ 803 $ 229 $ 93 Gross Increases - prior period tax positions — 59 — Gross Increases - current period tax positions 652 515 136 Total Unrecognized Benefit - end of period $ 1,455 $ 803 $ 229

Selected Unaudited Quarterly _2

Selected Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Summary of Unaudited Quarterly Financial Data	The following tables show a summary of the Company’s unaudited quarterly financial data for each of the four quarters of 2018 and 2017 (in thousands, except per share amounts): Three Months Ended December 31, 2018 September 30, 2018 June 30, 2018 March 31, 2018 Collaboration and service revenue $ — $ — $ 10,143 $ 497 Operating expenses 18,440 13,702 19,316 13,717 Other income (expense), net 846 855 826 563 Net loss (17,594 ) (12,847 ) (8,347 ) (12,657 ) Basic and diluted net loss per common share (1) $ (0.76 ) $ (0.56 ) $ (0.36 ) $ (0.72 ) Three Months Ended December 31, 2017 September 30, 2017 June 30, 2017 March 31, 2017 Collaboration and service revenue $ 2,775 $ 909 $ 449 $ 449 Operating expenses 12,252 9,244 6,674 6,004 Other income (expense), net 200 163 72 81 Net loss (9,277 ) (8,172 ) (6,153 ) (5,474 ) Basic and diluted net loss per common share (1) $ (1.80 ) $ (1.59 ) $ (1.21 ) $ (1.08 ) (1) Basic and diluted net loss per common share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted net loss per common share.

Formation and Business of the_2

Formation and Business of the Company (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Jan. 31, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Capitalization Equity [Line Items]
Proceeds from issuance initial public offering, net										$ 125,417
Net loss		$ (17,594)	$ (12,847)	$ (8,347)	$ (12,657)	$ (9,277)	$ (8,172)	$ (6,153)	$ (5,474)	(51,445)	$ (29,076)	$ (14,068)
Net cash used in operating activities										(52,733)	(28,222)	$ (2,265)
Cash, cash equivalents and investments		136,300								136,300
Accumulated deficit		$ (110,636)				$ (59,191)				$ (110,636)	$ (59,191)
IPO
Schedule Of Capitalization Equity [Line Items]
Shares issued (shares)	8,050,000
Proceeds from issuance initial public offering, net	$ 125,400
Over-Allotment Option
Schedule Of Capitalization Equity [Line Items]
Shares issued (shares)	1,050,000
Convertible Stock Converted into Shares of Common Stock
Schedule Of Capitalization Equity [Line Items]
Common shares issued upon conversion of convertible stock (shares)	9,629,405

Significant Accounting Polici_3

Significant Accounting Policies - Reverse Stock Split (Details)	Jan. 08, 2018
Common Stock
Class of Stock [Line Items]
Number of shares issued for every share converted in reverse stock split	0.3707

Significant Accounting Polici_4

Significant Accounting Policies - Segments (Details)	12 Months Ended
	Dec. 31, 2018Segment
Accounting Policies [Abstract]
Number of operating segments	1

Significant Accounting Polici_5

Significant Accounting Policies - Property and Equipment, Net (Details)	12 Months Ended
	Dec. 31, 2018
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of plant and equipment	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of plant and equipment	5 years

Significant Accounting Polici_6

Significant Accounting Policies - Additional Information (Details) - financial_institution	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Number of financial institutions holding majority of Company cash and cash equivalents and investments in excess of federally insured limits	2	2
Individual investment limit as a percentage of the total investment portfolio (percent)	5.00%

Significant Accounting Polici_7

Significant Accounting Policies - Revenue Recognition (Details)	12 Months Ended
	Dec. 31, 2018USD ($)
Accounting Policies [Abstract]
Revenues recognized refundable	$ 0

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	$ 134,562	$ 60,958
Corporate notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	41,035	46,098
Government notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	12,476	6,175
Asset backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	12,213
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market funds	$ 5,802	8,685
Net asset value	$ 1
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 63,036
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	5,802	19,963
Level 1 | Corporate notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments		5,103
Level 1 | Government notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments		6,175
Level 1 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market funds	5,802	8,685
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	128,760	40,995
Level 2 | Corporate notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	41,035	$ 40,995
Level 2 | Government notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	12,476
Level 2 | Asset backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	12,213
Level 2 | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 63,036

Fair Value Measurements (Availa

Fair Value Measurements (Available-for-Sale Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Money market funds, amortized cost	$ 49,510	$ 10,206	$ 4,027	$ 43,808
Amortized Cost	134,658	61,009
Unrealized Gains	2
Unrealized Losses	(98)	(51)
Fair Value	134,562	60,958
Corporate notes
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	41,103	46,133
Available-for-sale securities, unrealized gains	2
Available-for-sale securities, unrealized losses	(70)	(35)
Available-for-sale securities, fair value	41,035	46,098
Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	12,236
Available-for-sale securities, unrealized losses	(23)
Available-for-sale securities, fair value	12,213
Government notes
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	12,481	6,191
Available-for-sale securities, unrealized losses	(5)	(16)
Available-for-sale securities, fair value	12,476	6,175
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Money market funds, amortized cost	5,802	8,685
Money market funds	5,802	$ 8,685
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	63,036
Available-for-sale securities, fair value	$ 63,036

Balance Sheets Components (Deta

Balance Sheets Components (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accrued personnel expenses	$ 2,649	$ 1,108
Accrued clinical and development expenses	3,349	2,250
Other	256	201
Total	$ 6,254	$ 3,559

License Agreements (Details)

License Agreements (Details) $ in Millions	1 Months Ended			3 Months Ended	12 Months Ended
	May 31, 2018USD ($)	Aug. 31, 2016USD ($)Milestone	Dec. 31, 2012USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of milestones | Milestone		2
Merck
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement, milestone payments paid	$ 3
Merck | License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Licensing fee			$ 1
JT Torii
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accelerated recognition of deferred revenue, amount of revenue recognized				$ 8.1
Research and development arrangement, contract to perform for others, compensation earned				$ 2
JT Torii | Research and Development Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development arrangement, contract to perform for others, compensation earned					$ 10.6	$ 4.6	$ 0.7
Development and Regulatory Milestones | Merck
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangements, potential milestone payments			$ 25
Development and Regulatory Milestones | JT Torii
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangements, potential milestone proceeds		$ 28
Collaboration Agreement | JT Torii
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement, upfront payment received		11
Commercial Milestone | JT Torii
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangements, potential milestone proceeds		15
Development and Regulatory Milestone, Preparation of Investigational New Drug Submission, Milestone One | JT Torii
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangements, potential milestone proceeds		$ 2
Research and development arrangement, contract to perform for others, compensation earned					$ 2	$ 2

Commitments and Contingencies_2

Commitments and Contingencies (Details)	Oct. 01, 2017USD ($)ft²	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Acquired Indefinite-lived Intangible Assets [Line Items]
Operating lease, rent expense		$ 800,000	$ 400,000	$ 200,000
Redwood City, California
Acquired Indefinite-lived Intangible Assets [Line Items]
Operating lease, term of contract	30 months
Leased office space, square footage | ft²	14,000
Operating lease, monthly expense	$ 55,000

Commitments and Contingencies -

Commitments and Contingencies - Future Minimum Operating Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Year ending December 31:
2,019	$ 675
2,020	173
Total future minimum lease payments	$ 848

Convertible Preferred Stock (De

Convertible Preferred Stock (Details) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Jan. 31, 2018USD ($)shares	Jul. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2018USD ($)director$ / sharesshares	Dec. 31, 2017$ / sharesshares	Dec. 31, 2016shares	Dec. 31, 2015shares
Class of Stock [Line Items]
Preferred stock authorized (shares) | shares				28,322,761
Preferred stock, par value per share (in USD per share) | $ / shares				$ 0.001
Proceeds from issuance initial public offering, net | $			$ 125,417
Number of directors common shareholders are entitled to elect | director			3
Threshold proceeds of public stock offering of Company common shares that triggers automatic conversion of preferred convertible shares into common shares | $			$ 40,000
Threshold price per share in public stock offering of Company common shares that triggers automatic conversion of preferred convertible shares into common shares (in USD per share) | $ / shares			$ 17.21
IPO
Class of Stock [Line Items]
Proceeds from issuance initial public offering, net | $	$ 125,400
Shares issued (shares) | shares	8,050,000
Common shares issued upon conversion of convertible stock (shares) | shares	9,629,405
Over-Allotment Option
Class of Stock [Line Items]
Shares issued (shares) | shares	1,050,000
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock authorized (shares) | shares			0	14,300
Preferred stock, par value per share (in USD per share) | $ / shares			$ 0.001	$ 0.001
Convertible preferred stock outstanding (shares) | shares			0	14,300	14,300	14,300
Preferred stock, liquiditiy preference per share (in USD per share) | $ / shares			$ 1,000
Preferred stock, dividend per annum (in USD per share) | $ / shares			$ 80
Number of directors preferred shareholders are entitled to elect | director			2
Series B Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock authorized (shares) | shares			0	14,106,583
Preferred stock, par value per share (in USD per share) | $ / shares			$ 0.001	$ 0.001
Convertible preferred stock outstanding (shares) | shares			0	14,106,583	14,106,583	14,106,583
Preferred stock, liquiditiy preference per share (in USD per share) | $ / shares			$ 3.19
Preferred stock, dividend per annum (in USD per share) | $ / shares			$ 0.2552
Number of directors preferred shareholders are entitled to elect | director			2
Series C Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock authorized (shares) | shares			0	14,201,878
Preferred stock, par value per share (in USD per share) | $ / shares			$ 0.001	$ 0.001
Issuance of preferred stock (shares) | shares		11,854,463		11,854,463
Preferred shares issued, price per share (in USD per share) | $ / shares		$ 4.26
Proceeds from issuance initial public offering, net | $		$ 50,500
Convertible preferred stock outstanding (shares) | shares			0	11,854,463
Preferred stock, liquiditiy preference per share (in USD per share) | $ / shares			$ 4.26
Preferred stock, dividend per annum (in USD per share) | $ / shares			$ 0.3408
Number of directors preferred shareholders are entitled to elect | director			1
Convertible preferred stock
Class of Stock [Line Items]
Convertible preferred stock outstanding (shares) | shares			0

Common Stock (Details)

Common Stock (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Common stock authorized (shares)	300,000,000	55,000,000
Common stock, par value per share (in USD per share)	$ 0.0001	$ 0.0001

Stock-Based Compensation (Detai

Stock-Based Compensation (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 23, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		$ 3,638,000	$ 1,452,000	$ 573,000
Unamortized compensation expense		$ 11,900,000
Unamortized compensation expense, recognition period		3 years
Proceeds from the exercise of stock options		$ 496,000	34,000	0
Liability for early exercise of stock options		18,000	43,000
Aggregate grant date fair value of options vested during the year		2,600,000	500,000	200,000
Aggregate instrinsic value of shares exercised during the year		$ 1,800,000	$ 200,000	$ 0
Weighted average grant date fair value of options granted (in USD per share)		$ 5	$ 5.56	$ 1.79
Expected dividend yield		$ 0
Non-employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		$ 500,000	$ 600,000	$ 300,000
Expected dividend yield		0.00%	0.00%	0.00%
Employees and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield		0.00%	0.00%	0.00%
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		$ 1,734,000	$ 792,000	$ 257,000
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		$ 1,904,000	$ 660,000	$ 316,000
2011 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting period		4 years
2011 Stock Incentive Plan | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option expiration period		10 years
Option vesting period		4 years
2018 Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available under the Plan (shares)					3,000,000
Shares available for issuance under the Plan (shares)		1,319,109
2018 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available under the Plan (shares)	325,000
Purchase of common stock offer period under the plan	6 months
Discount rate from price of common stock on purchase date	15.00%
Commencement date to purchase common stock under the ESPP	Sep. 1, 2018
2018 Employee Stock Purchase Plan | Employees and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price of the award		$ 7.78
Expected option term		6 months
Expected volatility		2.13%
Risk-free interest rate		2.27%
Expected dividend yield		0.00%

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option and Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balances, beginning (shares)	2,506,926	1,485,132
Granted (shares)	1,700,013	1,040,329	1,485,132
Exercised (shares)	(255,186)	(18,535)
Forfeited/Expired (shares)	(46,283)
Balances, ending (shares)	3,905,470	2,506,926	1,485,132
Outstanding, exercise price per share (in USD per share)	$ 3.50	$ 1.99
Granted, exercise price per share (in USD per share)	7.58	5.56	$ 1.99
Exercised, exercise price per share (in USD per share)	1.94	1.83
Forfeited/expired, exercise price per share (in USD per share)	5.94
Outstanding, exercise price per share (in USD per share)	$ 5.35	$ 3.50	$ 1.99
Options outstanding, weighted average remaining contractual term	8 years 7 months 24 days	8 years 9 months 14 days	9 years 3 months 25 days
Options exercised, weighted average remaining contractual term		8 years 9 months 14 days
Options outstanding, aggregate intrinsic value	$ 24,033	$ 3,805
Options outstanding, aggregate intrinsic value	2,509	24,033	$ 3,805
Exercised, aggregate intrinsic value	$ 1,800	$ 200	$ 0
Early Exercised Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised (shares)			(317,405)
Unvested options included in early exercise (shares)	59,513	139,636

Stock-Based Compensation - Fair

Stock-Based Compensation - Fair Value Assumptions for Director, Employee and Non-Employee Grants (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employees and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility, minimum (percent)	72.00%	75.00%	68.00%
Volatility, maximum (percent)	73.00%	100.00%	74.00%
Risk-free interest rate, minimum (percent)	2.80%	1.90%	1.30%
Risk-free interest rate, maximum (percent)	3.00%	2.30%	2.10%
Dividend yield (percent)	0.00%	0.00%	0.00%
Employees and Directors | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years	6 years	4 years 7 months 6 days
Employees and Directors | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
Non-employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility, minimum (percent)	68.00%	74.00%	84.00%
Volatility, maximum (percent)	79.00%	100.00%	86.00%
Risk-free interest rate, minimum (percent)	2.80%	2.10%	1.60%
Risk-free interest rate, maximum (percent)	3.00%	2.50%	2.50%
Dividend yield (percent)	0.00%	0.00%	0.00%
Non-employees | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	7 years 3 months 18 days	8 years 3 months 18 days	9 years 3 months 18 days
Non-employees | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	10 years	10 years	10 years

Net Loss per Share Attributab_3

Net Loss per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net loss attributable to common stockholders, basic									$ (51,445)	$ (29,076)	$ (14,068)
Weighted-average common shares outstanding									21,764,636	5,285,542	5,280,058
Less: weighted-average common shares subject to repurchase									(95,947)	(177,421)	(292,925)
Weighted-average common shares used to compute basic and diluted net loss per share									21,668,689	5,108,121	4,987,133
Net loss attributable to common stockholders per share, basic and diluted	$ (0.76)	$ (0.56)	$ (0.36)	$ (0.72)	$ (1.80)	$ (1.59)	$ (1.21)	$ (1.08)	$ (2.37)	$ (5.69)	$ (2.82)

Net Loss per Share Attributab_4

Net Loss per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from the calculation of EPS	4,024,718	12,275,967	6,942,009
Convertible preferred stock issuable upon conversion to common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from the calculation of EPS		9,629,405	5,234,800
Outstanding common stock subject to repurchase
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from the calculation of EPS	59,513	139,636	222,077
Stock options outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from the calculation of EPS	3,905,470	2,506,926	1,485,132
Shares issuable related to ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from the calculation of EPS	59,735

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
NOLs	$ 22,248	$ 10,404	$ 10,458
Depreciation and Amortization	241	226	328
Stock-Based Compensation	627	274	161
Research & Development Credits	3,972	2,063	586
Deferred Revenue		1,791	0
Other Accruals	507	235	98
Total Deferred Tax Assets	27,595	14,993	11,631
Valuation Allowance	(27,595)	(14,993)	(11,631)
Net Deferred Tax Assets	$ 0	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Increase in valuation allowance	$ 12,600	$ 3,400	$ 5,000
Accrued interest and penalties related to uncertain tax positions	$ 0
Statutory rate	21.00%	34.00%
Reduction in deferred tax assets resulting from the rate reduction		$ 7,000
Federal Tax
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 100,600	44,300
State Tax
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	16,800	15,000
Research Development Tax Credit | Federal Tax
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	4,100	2,100
Research Development Tax Credit | State Tax
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 1,400	$ 900

Income Taxes - Uncertain Tax Po

Income Taxes - Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Unrecognized Benefit beginning of period	$ 803	$ 229	$ 93
Gross Increases - prior period tax positions		59	0
Gross Increases - current period tax positions	652	515	136
Unrecognized Benefit - end of period	$ 1,455	$ 803	$ 229

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Accounts payable		$ 0	$ 0
Velocity Pharmaceutical Development, LLC | Development Services Fees
Related Party Transaction [Line Items]
Related party expenses	$ 1,000,000

Selected Unaudited Quarterly _3

Selected Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Collaboration and service revenue			$ 10,143	$ 497	$ 2,775	$ 909	$ 449	$ 449	$ 10,640	$ 4,582	$ 674
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses	$ 18,440	$ 13,702	$ 19,316	$ 13,717	$ 12,252	$ 9,244	$ 6,674	$ 6,004	$ 65,175	$ 34,175	$ 15,006
Other income (expense), net	846	855	826	563	200	163	72	81
Net loss	$ (17,594)	$ (12,847)	$ (8,347)	$ (12,657)	$ (9,277)	$ (8,172)	$ (6,153)	$ (5,474)	$ (51,445)	$ (29,076)	$ (14,068)
Net loss attributable to common stockholder per share, basic and diluted	$ (0.76)	$ (0.56)	$ (0.36)	$ (0.72)	$ (1.80)	$ (1.59)	$ (1.21)	$ (1.08)	$ (2.37)	$ (5.69)	$ (2.82)