Sierra Oncology (SRRA) 10-K 3 Mar 20 2019 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Feb. 26, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	Sierra Oncology, Inc.
Entity Central Index Key	0001290149
Trading Symbol	SRRA
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true
Entity Common Stock, Shares Outstanding		10,395,732
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock
Entity Address, State or Province	BC
Entity Address, Country	CA
Entity Public Float			$ 36.8

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
CURRENT ASSETS:
Cash and cash equivalents	$ 147,528	$ 106,046
Prepaid expenses and other current assets	2,369	2,706
Total current assets	149,897	108,752
Property and equipment, net	113	168
Operating lease right-of-use asset	589
Other assets	729	549
TOTAL ASSETS	151,328	109,469
CURRENT LIABILITIES:
Accrued and other liabilities	7,170	8,812
Accounts payable	1,019	1,287
Warrant liabilities	45,935
Securities issuance obligation	10,485
Total current liabilities	64,609	10,099
Operating lease liability	374
Term loan		4,891
TOTAL LIABILITIES	64,983	14,990
Commitments and Contingencies (Note 8)
STOCKHOLDERS' EQUITY:
Preferred stock, $0.001 par value; 10,000,000 shares authorized as of December 31, 2019 and December 31, 2018; 103,000 shares Series A convertible voting preferred stock, issued and outstanding as of December 31, 2019 and nil shares issued and outstanding as of December 31, 2018	1
Common stock, $0.001 par value; 500,000,000 shares authorized as of December 31, 2019 and 2018; 1,867,176 and 1,859,120 shares issued and outstanding as of December 31, 2019 and 2018	74	74
Additional paid-in capital	851,957	771,817
Accumulated deficit	(765,687)	(677,412)
TOTAL STOCKHOLDERS' EQUITY	86,345	94,479
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 151,328	$ 109,469

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	1,867,176	1,859,120
Common stock, shares outstanding	1,867,176	1,859,120
Series A Convertible Preferred Stock [Member]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	103,000	0
Preferred stock, shares outstanding	103,000	0

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 53,249	$ 41,078	$ 30,157
General and administrative	13,743	14,339	12,462
Total operating expenses	66,992	55,417	42,619
Loss from operations	(66,992)	(55,417)	(42,619)
Other income (expense), net:
Changes in fair value of warrant liabilities	(20,926)
Other income (expense), net	(517)	1,780	760
Total other income (expense)	(21,443)	1,780	760
Loss before provision for (benefit from) income taxes, net	(88,435)	(53,637)	(41,859)
Provision for (benefit from) income taxes, net	(160)	(302)	156
Net loss and comprehensive loss	$ (88,275)	$ (53,335)	$ (42,015)
Net loss per common share, basic and diluted	$ (30.30)	$ (30.16)	$ (33.68)
Weighted-average shares used in computing net loss per common share, basic and diluted	2,913,487	1,768,480	1,247,482

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Convertible Voting Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Stockholders Equity, Ending Balance at Dec. 31, 2016	$ 103,248		$ 30	$ 685,272	$ (582,054)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2016			759,253
Issuance of common stock for exercise of stock options	166			166
Issuance of common stock for exercise of stock options, Shares			4,413
Cumulative effect of adoption of new accounting standard at Dec. 31, 2016				8	(8)
Stock-based compensation	5,905			5,905
Issuance of common stock, net of offering costs	27,422		$ 22	27,400
Issuance of common stock, net of offering costs, Shares			546,190
Net loss	(42,015)				(42,015)
Stockholders Equity, Ending Balance at Dec. 31, 2017	94,726		$ 52	718,751	(624,077)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2017			1,309,856
Issuance of common stock for exercise of stock options	180			180
Issuance of common stock for exercise of stock options, Shares			3,014
Stock-based compensation	6,796			6,796
Issuance of common stock, net of offering costs	45,996		$ 22	45,974
Issuance of common stock, net of offering costs, Shares			546,250
Issuance of common stock warrant	116			116
Net loss	(53,335)				(53,335)
Stockholders Equity, Ending Balance at Dec. 31, 2018	94,479		$ 74	771,817	(677,412)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2018			1,859,120
Issuance of common stock for exercise of stock options	445			445
Issuance of common stock for exercise of stock options, Shares			8,056
Stock-based compensation	5,695			5,695
Issuance of convertible voting preferred stock, net of offering costs	74,001	$ 1		74,000
Issuance of convertible voting preferred stock, net of offering costs, shares		103,000
Net loss	(88,275)				(88,275)
Stockholders Equity, Ending Balance at Dec. 31, 2019	$ 86,345	$ 1	$ 74	$ 851,957	$ (765,687)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2019		103,000	1,867,176

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net of offering costs		$ 3.2	$ 2.1
Series A Convertible Preferred Stock [Member]
Net of offering costs	$ 4

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (88,275)	$ (53,335)	$ (42,015)
Adjustments to reconcile net loss to net cash used in operating activities:
Changes in fair value of warrant liabilities	20,926
Securities issuance obligation	10,485
Stock-based compensation	5,695	6,796	5,905
Warrant issuance costs	1,279
Term loan repayment fee	438
Depreciation and amortization	83	111	258
Other	161	(68)	31
Changes in operating assets and liabilities:
Prepaid expenses and other assets	336	(1,341)	(115)
Accrued, other and operating lease liabilities	(2,034)	2,770	990
Accounts payable	(277)	(48)	(1,217)
Net cash used in operating activities	(51,183)	(45,115)	(36,163)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(39)	(118)	(92)
Net cash used in investing activities	(39)	(118)	(92)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from public offering, net of offering costs	97,731
Payment of term loan and repayment fee	(5,438)
Proceeds from exercise of common stock options	445	180	166
Proceeds from issuance of common stock upon follow-on offering, net of offering costs		45,996	27,422
Proceeds from issuance of term loan, net of issuance costs		4,955
Net cash provided by financing activities	92,738	51,131	27,588
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(34)	(88)	(4)
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	41,482	5,810	(8,671)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—Beginning of period	106,346	100,536	109,207
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—End of period	147,828	106,346	100,536
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for (refund of) income taxes, net	(69)	15	$ 260
Cash paid for interest	336	87
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Right-of-use asset obtained in exchange for operating lease obligation	771
Issuance costs of convertible voting preferred stock and warrants included in accrued and other liabilities	$ 268
Issuance of common stock warrant		$ 116

The Company and Basis of Presen

The Company and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company and Basis of Presentation	1. The Company and Basis of Presentation Organization and Description of Business Sierra Oncology, Inc. (together with its subsidiaries, collectively referred to as the “Company”), a Delaware corporation, is a late stage drug development company focused on advancing its lead product candidate, momelotinib, a potent, selective and orally-bioavailable JAK1 (Janus kinase 1), JAK2 (Janus kinase 2) and ACVR1 (Activin A receptor type 1) inhibitor with a potentially differentiated therapeutic profile for the treatment of myelofibrosis. Momelotinib has been investigated in two completed Phase 3 clinical trials for the treatment of myelofibrosis and has demonstrated a potentially differentiated therapeutic profile encompassing anemia-related clinical benefits, as well as achieving constitutional symptom control benefits and substantive splenic volume reductions. The Company’s portfolio also includes two DNA Damage Response (DDR) assets, consisting of SRA737 and SRA141. SRA737 is a potent, highly selective, orally bioavailable small molecule inhibitor of Checkpoint kinase 1 (Chk1), a key regulator of cell cycle progression and the DDR network. SRA141 is a potent, selective and orally bioavailable small molecule inhibitor of Cell division cycle 7 kinase (Cdc7), a key regulator of DNA replication and involved in the DDR network. The Company’s primary activities since inception have been conducting research and development activities, conducting preclinical and clinical testing, recruiting personnel, performing business and financial planning, identifying and evaluating additional drug candidates for potential in-licensing The Company has not generated any product revenue related to its primary business purpose to date, nor has it generated any income, and is subject to a number of risks and uncertainties, which include dependence on key individuals, the need to identify and successfully develop commercially viable products, the need to obtain regulatory approval for its products and commercialize them, and the need to obtain adequate additional financing to fund the development of its product candidates. As of December 31, 2019, the Company had $147.5 million of cash and cash equivalents. The Company believes that its balance of cash and cash equivalents as of the date of the issuance of these consolidated financial statements is sufficient to fund its current operational plan for at least the next twelve months though it may pursue raising additional capital through equity financings or other arrangements. Follow-On On February 14, 2017, the Company completed an underwritten public offering of 487,500 shares of common stock. As part of the underwritten public offering, on February 21, 2017 the Company issued an additional 58,690 shares of common stock representing the underwriters’ exercise of a majority of their over-allotment option. All shares were offered by the Company at a price to the public of $54.00 per share. The aggregate net proceeds received by the Company from the offering were $27.4 million, net of underwriting discounts and commissions and offering expenses of $2.1 million. On March 6, 2018, the Company completed an underwritten public offering of an aggregate of 546,250 shares of common stock, including the underwriters’ exercise of their overallotment option, at a price to the public of $90.00 per share. The aggregate net proceeds received by the Company from the offering were $46.0 million, net of underwriting discounts and commissions and offering expenses of $3.2 million. On November 13, 2019, the Company completed an underwritten public offering of an aggregate of (i) 103,000 shares of Series A convertible voting preferred stock (Series A Preferred Stock), P S 29 shares of Preferred Stock into Reverse Stock Split O 21 approved 22 1-for-40.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP). The accompanying consolidated financial statements include the accounts of Sierra Oncology, Inc. and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates The preparation of the consolidated 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 consolidated financial statements and the reported amounts of expense during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include, but are not limited to the fair value of convertible voting preferred stock, stock options and warrants issued, fair value of the securities issuance obligation, accruals such as research and development costs, and recoverability of the Company’s net deferred tax assets, and related valuation allowance. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates. Foreign Currency The functional currency of the Company’s foreign subsidiaries is the U.S. Dollar. Transactions denominated in currencies other than the functional currency are recorded at prevailing exchange rates during the period. At the end of each reporting period, monetary assets and liabilities are remeasured to the functional currency using exchange rates in effect at the balance sheet date. Non-monetary Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents. Cash and cash equivalents consist primarily of funds invested in readily available checking and savings accounts and highly liquid investments in money market funds. Restricted Cash Restricted cash, which consists of funds invested in a money market fund, represents collateral for a corporate credit card facility and is included in other assets in the accompanying consolidated balance sheets. Concentrations of Credit Risk Financial instruments that subject the Company to significant concentrations of credit risk consist of cash, cash equivalents and restricted cash. All of the Company’s cash, cash equivalents and restricted cash are held at financial institutions in the United States and Canada that management believes to be of high credit quality. Deposits held in the United States and Canada with these financial institutions exceed federally insured limits. The primary focus of the Company’s investment strategy is to preserve capital and meet liquidity requirements. The Company’s investment policy addresses the level of credit exposure by limiting the concentration in any one corporate issuer and establishing a minimum allowable credit rating. Fair Value of Financial Instruments The Company’s cash and cash equivalents, restricted cash, other current assets, accounts payable and accrued liabilities approximate their fair values at December 31, 2019 and 2018, due to their short duration. Prior to its repayment in December 2019, the term loan bore interest at prevailing market rates for instruments with similar characteristics, accordingly, the carrying value of this instrument approximated its fair value. The warrant liabilities and securities issuance obligation contain unobservable inputs that reflect the Company’s own assumptions in which there is little, if any, market activity at the measurement date, thus the Company’s warrant liabilities and securities issuance obligation are measured at their fair values on a recurring basis using unobservable inputs. The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines the fair value of its financial instruments based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels: Level 1 Level 2 Level 3 Property and Equipment, Net Property and equipment, net are stated at cost, less accumulated depreciation. Depreciation on property and equipment, excluding leasehold improvements, is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful lives of the assets or the remaining lease term. Depreciation begins at the time the asset is placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations. Other Assets Other assets consist primarily of restricted cash pledged as collateral for a corporate credit card facility Operating Lease Right-of-Use Asset On January 1, 2019, the Company adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) and non-lease components The Company recognizes an operating lease with terms greater than one year as right-of-use (ROU) Warrant Liabilities The Company accounts for its warrants issued in connection with its November 2019 financing based upon the characteristics and provisions of the instruments. Warrants classified as derivative liabilities are recorded on the Company’s consolidated balance sheets at their fair value on the date of issuance and remeasured to fair value on each subsequent reporting period, with the changes in fair value recognized as a component of other income (expense), net in the accompanying consolidated statements of operations. The Company will continue to adjust the carrying value of the warrants until such time as the warrants are no longer considered derivative instruments, or until the earlier of the exercise of the warrants or the expiration of the warrants, at which time the liabilities will be reclassified to additional paid-in non-marketable Securities Issuance Obligation The Company recognizes its securities issuance obligation pursuant to the amendment to the Asset Purchase Agreement with Gilead Sciences, Inc. (Gilead) at their fair values on the date such obligations arose. At the end of each reporting period, changes in estimated fair values during the period are recognized as research and development costs in the accompanying consolidated statements of operations. The Company will continue to adjust the fair values of the obligations until the securities are issued, at which time the liabilities will be reclassified to common stock and additional paid-in non-marketable non-marketable Research and Development Costs Research and development costs are expensed as incurred. The Company accounts for non-refundable Upfront payments made in connection with license and asset purchase agreements are expensed as research and developments costs, as the assets acquired do not have alternative future use. Contingent milestone payment obligations due to third parties under license and asset purchase agreements are expensed when the milestones are considered probable of occurring. To the extent an obligation is to be settled by future issuance of securities, the fair value of these instruments is recorded in research and development expense until the securities are issued. Research and development costs include fees incurred in connection with license and asset purchase agreements and their related amendments, compensation and other related costs for employees engaged in research and development, costs associated with research and preclinical studies, clinical trials, regulatory activities, manufacturing activities to support clinical activities, fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company and an allocation of overhead expenses. Stock-Based Compensation The Company accounts for stock-based payments at fair value, which is measured using the Black-Scholes option-pricing model. For stock-based awards that vest subject to the satisfaction of a service requirement, the fair value measurement date for stock-based compensation awards is the date of grant and the expense is recognized on a straight-line basis over the vesting period, which is generally the service period. The Company accounts for forfeitures as they occur. On January 1, 2019, the Company adopted FASB ASU No. 2018-07 , Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, Income Taxes The Company uses the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Management makes an assessment of the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s historical operating performance and the recorded cumulative net losses in prior fiscal periods, the net U.S. deferred tax assets have been offset by a full valuation allowance. The Company recognizes uncertain income tax positions at the largest amount that is more likely than not to be sustained upon audit by the relevant taxing authority. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained. Changes in recognition or measurement are reflected in the period in which judgment occurs. The Company recognizes interest and penalties related to the underpayment of income taxes as a component of provision for (benefit from) income taxes, net. Segment Information Operating segments are components of an enterprise for which separate financial information is available and is evaluated regularly by the Company’s chief operating decision maker in deciding how to allocate resources and assessing performance. The Company’s chief operating decision maker is its Chief Executive Officer. The Company’s Chief Executive Officer views the Company’s operations and manages its business in one

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	3. Net Loss Per Share Basic net loss per share is calculated by dividing net loss by the weighted-average number of common stock and preferred stock with characteristics of common stock outstanding during the period without consideration for common stock equivalents. Diluted net loss per share is computed by dividing net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, stock options and warrants for common stock are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. The following shares of common stock equivalents were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been antidilutive: As of December 31, 2019 2018 2017 Series A warrants for common stock 7,802,241 — — Series B warrants for common stock 2,574,727 — — Stock options to purchase common stock 326,023 262,539 186,710 Warrant for common stock 1,839 1,839 — Total potential dilutive shares 10,704,830 264,378 186,710

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The Company measures and reports its cash equivalents, restricted cash, warrant liabilities and securities issuance obligation December 31, 2019 Level 1 Level 2 Level 3 Total (in thousands) Financial Assets Money market funds $ 146,240 $ — $ — $ 146,240 Restricted money market funds 300 — — 300 Total financial assets $ 146,540 $ — $ — $ 146,540 Financial Liabilities Warrant liabilities $ — $ — $ 45,935 $ 45,935 Securities issuance obligation — — 10,485 10,485 Total financial liabilities $ — $ — $ 56,420 $ 56,420 December 31, 2018 Level 1 Level 2 Level 3 Total (in thousands) Financial Assets Money market funds $ 105,224 $ — $ — $ 105,224 Restricted money market funds 300 — — 300 Total financial assets $ 105,524 $ — $ — $ 105,524 Money market funds and restricted money market funds are measured at fair value on a recurring basis using quoted prices and are classified as a Level 1 input. The Company’s warrant liabilities and securities issuance obligation contain unobservable inputs that reflected the Company’s own assumptions in which there is little, if any, market activity at the measurement date. Accordingly, the Company’s warrant liabilities and securities issuance obligation are measured at fair value on a recurring basis using unobservable inputs at each reporting period. The warrant liabilities and securities issuance obligation are classified as Level 3 inputs. These liabilities are shown as current liabilities on the balance sheet as they are deemed more probable than not by management to be settled within one year. The fair values of the Series A and Series B warrants are estimated using the Black-Scholes option-pricing model. The expected terms represent the periods that the warrants are expected to be outstanding. The risk-free interest rates are based on the U.S. Constant Maturity treasury curve commensurate with the time to expiry. The expected dividend is zero as the Company has not paid nor does it anticipate paying any dividends on its common stock in the foreseeable future. The expected volatilities are estimated by backsolving to volatility implied in the transaction price. Discount for lack of marketability is dependent on the restriction period and the estimated volatility during the period. The fair value of the warrant issuance obligation is estimated using the Black-Scholes option-pricing model. The expected term represents the period that the underlying warrant is expected to be outstanding from the time the issuance obligation arose. The risk-free interest rate is based on the U.S. Constant Maturity treasury curve commensurate with the time to expiry. The expected dividend is zero as the Company has not paid nor does it anticipate paying any dividends on its common stock in the foreseeable future. The expected volatility is estimated by backsolving to volatility implied in the transaction price. The fair value of the common stock issuance obligation is estimated based on the fair value of the underlying common stock. Discount for lack of marketability is dependent on the restriction period and the estimated volatility during the period. The assumptions used in calculating the estimated fair values at the end of the reporting period represent the Company’s best estimate. However, inherent uncertainties are involved. If factors or assumptions change, the estimated fair values could be materially different. At November 13, 2019, the Company estimated the fair values of the financial liabilities using the following assumptions: Series A Warrant Series B Warrant Warrant Issuance Common Stock Expected term (in years) 5.2 2.3 5.2 N/A Expected volatility 43 % 88 % 43 % N/A Risk-free interest rate 1.70 % 1.64 % 1.70 % N/A Expected dividend yield — % — % — % N/A Discount for lack of marketability 30 % 30 % 32 % 32 % At December 31, 2019, the Company remeasured these liabilities to their fair values using the following assumptions: Series A Warrant Series B Warrant Warrant Issuance Common Stock Expected term (in years) 5.1 2.2 5.1 N/A Expected volatility 43 % 88 % 43 % N/A Risk-free interest rate 1.69 % 1.59 % 1.70 % N/A Expected dividend yield — % — % — % N/A Discount for lack of marketability 25 % 25 % 25 % 25 % The following table provides a summary of changes in the estimated fair values of the Company’s Level 3 financial liabilities, which are measured at fair value on a recurring basis using unobservable inputs: Series A Warrant Series B Warrant Warrant Issuance Common Stock Total (in thousands) Balance, December 31, 2018 $ — $ — $ — $ — $ — Issuance of warrants 17,133 7,876 — — 25,009 Securities issuance obligation 1,543 4,903 6,446 Changes in fair value 15,483 5,443 1,493 2,546 24,965 Balance, December 31, 2019 $ 32,616 $ 13,319 $ 3,036 $ 7,449 $ 56,420 The warrant liabilities will increase or decrease each reporting period based on fluctuations of the fair value of the underlying common stock until such time these financial liabilities are no longer considered derivative instruments, or the earlier of settlement and expiration of warrants. The change in the fair value of warrant liabilities for each presented period is recognized as a component of other income (expense), net in the consolidated statements of operations. The securities issuance obligation will increase or decrease each reporting period based on fluctuations of the fair value of the underlying common stock until such time the securities are issued. The change in fair values of securities issuance obligation is recognized as research and development expense in the consolidated statement of operations. There were no transfers between Levels 1, 2 or 3 during the years ended December 31, 2019 and 2018.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	5. Balance Sheet Components Cash and Cash Equivalents Cash and cash equivalents consist of the following: December 31, 2019 2018 (in thousands) Cash $ 1,288 $ 822 Cash equivalents: Money market accounts 146,240 105,224 Total cash and cash equivalents $ 147,528 $ 106,046 The following table provides a reconciliation of cash, cash equivalents and restricted cash reported in the consolidated balance sheets to the amounts shown in the consolidated statements of cash flows. December 31, 2019 December 31, (in thousands) Cash and cash equivalents $ 147,528 $ 106,046 Restricted cash included in other assets 300 300 Total cash, cash equivalents and restricted cash shown in the consolidated statement of cash flows $ 147,828 $ 106,346 Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist of the following: December 31, 2019 2018 (in thousands) Prepaid insurance $ 918 $ 555 Prepaid research and development project costs 853 762 Other receivables 190 751 Income taxes receivable 7 163 Other 401 475 Total prepaid expenses and other current assets $ 2,369 $ 2,706 Property and Equipment, net Property and equipment, net consists of the following: December 31, 2019 2018 (in thousands) Software $ 352 $ 325 Leasehold improvements 112 112 Computer equipment 89 89 Furniture and fixtures 3 3 Property and equipment, gross 556 529 Less: accumulated depreciation (443 ) (361 ) Total property and equipment, net $ 113 $ 168 Depreciation related to the Company’s property and equipment for the years ended December 31, 2019, 2018 and 2017 was $0.1 million, $0.1 million and $0.3 million, respectively. Accrued Liabilities Accrued liabilities consist of the following: December 31, 2019 2018 (in thousands) Accrued employee related costs $ 3,420 $ 3,223 Accrued research and development costs 2,668 4,485 Accrued professional fees 817 357 Operating lease liability 187 — Other 78 747 Total accrued liabilities $ 7,170 $ 8,812

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	6. Leases In June 2017, the Company entered into an operating lease agreement to lease the office space in Vancouver, Canada commencing March 1, 2018. The lease expires on February 28, 2023 and can be extended for an additional term of 5 years. In January 2016, the Company entered into an operating lease agreement to lease office space near San Francisco, California. In September 2017, the Company entered into a sublease agreement to sublet the premises to a third party. Both the operating lease and sublease agreements expired on April 30, 2019. On January 1, 2019, with the adoption of ASU 2016-02, right-of-use The components of lease expense and related cash flows for the year ended December 31, 2019 were as follows: Year Ended December 31, 2019 Operating lease cost $ 203 Short-term lease cost 117 320 Operating cash flows used for operating leases $ 198 The total rent expense was $0.5 million for the year s a nd 2017 As of December 31, 2019, the weighted average remaining lease term and discount rate for the operating lease are 3.2 years and 6.5%, respectively. As of December 31, 2019, maturities of lease liability due under the lease agreement are as follows: Years Ending December 31: Operating (in thousands) 2020 217 2021 221 2022 177 Total lease payments 615 Less imputed interest (54 ) Total $ 561 In addition to base rent, these leases require payment of non-lease non-component

Term Loan

Term Loan	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Term Loan	7. Term Loan I during 2019 On December 18, 2019, the Company repaid the $5.0 million term loan and paid the $0.1 million and $0.3 millio n, respectively The Company recognized interest expense related to the Loan Agreement of $0.9 million

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Asset Purchase Agreement In August 2018, the Company entered into an Asset Purchase Agreement with Gilead whereby the Company acquired worldwide rights to the pharmaceutical product momelotinib, an investigational orally-bioavailable JAK1, JAK2 and ACVT1 inhibitor together with all related intellectual property rights and certain other related assets. Pursuant to the agreement, the Company made a one-time million in August 2018. The related expense was included in research and development for the year ended December 31, 2018 in the accompanying consolidated statement of operations. In October 2019, the Company entered into an amendment to the Asset Purchase Agreement in which the Company agreed to issue, subject to certain conditions, shares of common stock and a warrant to purchase common stock to Gilead in consideration for meaningfully reduced royalty rates and elimination of a near term milestone payment in the Asset Purchase Agreement. Pursuant to the amended agreement, milestone payments of up to an aggregate of million may become payable to Gilead upon the achievement of certain regulatory and commercial milestone events and the Company is now required to pay Gilead low double-digit to high-teens percent tiered combined royalties based upon net sales. The effectiveness of the amendment and the issuance of the shares of common stock and warrant to Gilead was conditional upon the completion of an offering that closed in November 2019. In connection with obligations under the amendment, the Company initially recognized a $6.5 non-cash non-cash Note 4, Fair Value Measurement for further discussions in valuation techniques . On January 31, 2020, the Company fulfilled the obligation to issue securities by entering into a securities purchase agreement with Gilead, pursuant to which the Company issued to Gilead 725,283 shares of the Company’s common stock and a warrant to purchase 725,283 common stock at a price per share of $13.20 . The warrant is immediately exercisable, will expire on January 31, 2025 and contains a cash and/or cashless exercise provision. License Agreements In September 2016, the Company entered into an exclusive license agreement with CRT Pioneer Fund LP (CPF) for worldwide rights, know-how and a one-time upfront product-by-product country-by-country In May 2016, the Company entered into an exclusive license agreement (Carna License Agreement) with Carna Biosciences, Inc. (Carna) for worldwide rights to develop and commercialize SRA141, a small molecule kinase inhibitor targeting Cdc7. In exchange for this exclusive right, the Company paid Carna an upfront payment of $0.9 million in June 2016. The Company will be required to pay Carna milestone payments of up to an aggregate of $270.0 million upon achievement of certain developmental, regulatory and commercial milestone events, including a milestone payment of $4.0 million upon dosing of the first patient in the first Phase 1 clinical trial for SRA141. These milestones will be accrued once they are considered probable of occurring. As of December 31, 2019, the Company had not recorded any milestone payments to Carna. In addition, the Company is required to pay Carna tiered single-digit royalties on net sales of product candidates (as defined under the Carna License Agreement). Legal From time to time, the Company may become subject to other legal proceedings, claims and litigation arising in the ordinary course of business. In addition, the Company may receive letters alleging infringement of patent or other intellectual property rights. The Company is not currently a party to any other material legal proceedings, nor is it aware of any pending or threatened litigation that, in the Company’s opinion, would have a material adverse effect on the business, operating results, cash flows or financial condition should such litigation be resolved unfavorably.

Common Stock Reserved for Issua

Common Stock Reserved for Issuance	12 Months Ended
	Dec. 31, 2019
Stockholders' Equity Note Disclosure	9. Common Stock Reserved for Issuance The Company is required to reserve and keep available out of its authorized but unissued shares of common stock a number of shares sufficient to effect the conversion of all outstanding preferred stock, options granted and available for grant under the incentive plans, shares reserved for issuance under the employee stock purchase plan and issued warrant. December 31, 2019 2018 Shares reserved for conversion of Series A Preferred Stock 7,803,273 — Shares reserved under Series A warrant 7,802,241 — Shares reserved under Series B warrant 2,574,727 — Outstanding stock options under equity incentive plans 326,023 262,539 Shares reserved for future option grants under equity plans 51,514 48,689 Shares reserved under the 2015 employee stock purchase plan 17,500 17,500 Shares reserved under warrant upon contingent events — 3,677 Outstanding warrant 1,839 1,839 Total common stock reserved for issuance 18,577,117 334,244 On January 21, 2020 the Company’s stockholders approved an increase to the authorized number of shares available for issuance under the 2015 Equity Incentive Plan by 4,312,500 (see Note 12). On January 31, 2020 the Company fulfilled its securities issuance obligation and issued Gilead 725,283 shares of the Company’s common stock and a warrant to purchase 725,283 common stock (see Note 8).

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2019
Preferred Stock [Member]
Stockholders' Equity Note Disclosure	10. Preferred Stock As of December 31, 2019, the Company had 10,000,000 shares of preferred stock authorized with a par value of $0.001. There were 103,000 shares of Series A Preferred Stock outstanding as of December 31, 2019. There were no shares of preferred stock issued and outstanding as of December 31, 2018. Series A Convertible Voting Preferred Stock On November 13, 2019, the Company issued 103,000 shares of Series A Preferred Stock together with Series A warrants and Series B warrants for a combined purchase price of $1,000 . The aggregate proceeds received by the Company was $97.7 million, net of underwriting discounts and commissions and offering expenses. Each share of Series A Preferred Stock is convertible into shares of the Company’s common stock equal to the stated value of the Series A Preferred Stock of $1,000 divided by the voting conversion price of $13.20. Each share of Series A Preferred Stock will convert into shares of common stock (i) at the option of the holder or (ii) automatically upon the fifth day of trading following the announcement of the stockholder approval for a Reverse Stock Split, subject to certain beneficial ownership limitations. The Series A Preferred Stock will initially vote together with the Company’s common stock on an as-converted In the event of any voluntary or involuntary liquidation, dissolution, winding up of the Company or sale event, the assets of the Company available for distribution to its stockholders shall be distributed among the holders of the shares of Series A Preferred Stock and common stock, pro rata based on the number of shares held by each such holder. On January 29, 2020, all shares of Series A Preferred Stock converted into 7,803,273 shares of the Company’s common stock.

Warrant Liabilities

Warrant Liabilities	12 Months Ended
	Dec. 31, 2019
Warrants and Rights Note Disclosure [Abstract]
Warrant Liabilities	11. Warrant Liabilities In connection with the Company’s November 2019 public offering of the Series A Preferred Stock, the Company issued Series A warrants to purchase up to shares of common stock at an exercise price equal to , and Series B warrants to purchase up to shares of common stock at an exercise price equal to $ . Both Series A and Series B warrants are exercisable following stockholder approval of an increase in authorized common stock sufficient to allow for the exercise of the warrants, subject to certain beneficial ownership limitations. The Series A warrants will five years from the date they first became exercisable or on January 22, 2025 and contain a cash and /or th top-line , which would amount to approximately $34.0 million in proceeds to the Company if fully exercised. The fair value s warrant liabilities a non-cash

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	12. Stock-Based Compensation In the accompanying consolidated statement of operations, the Company recognized stock-based compensation expense for its employees and non-employees Year Ended December 31, 2019 2018 2017 (in thousands) Research and development $ 3,873 $ 4,499 $ 3,966 General and administrative 1,822 2,297 1,939 Total stock-based compensation $ 5,695 $ 6,796 $ 5,905 ASU No. 2018-07 , Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, Determination of Fair Value The estimated grant-date fair value of all the Company’s stock-based awards was calculated using the Black-Scholes option pricing model, based on the following assumptions: Year Ended December 31, 2019 2018 2017 Expected term (in years) 5.3 – 5.3 – 5.3 – Expected volatility 89 – % 88 – % 86 – % Risk-free interest rate 1.6 – % 2.6 – % 1.8 – % Expected dividend rate — % — % — % The fair value of each stock option grant was determined by the Company on the date of grant using the methods and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment and estimation by management. Expected Term— Expected Volatility— Risk-Free Interest Rate— zero-coupon Expected Dividend Rate— Forfeiture Rate— Equity Incentive Plans 2018 Equity Inducement Plan In September 2018, the Company’s Compensation Committee approved the 2018 Equity Inducement Plan (2018 Plan). The number of shares available for awards under the 2018 Plan was set to 37,500. The exercise price of each stock-based award issued under the 2018 Plan is required to be no less than the fair value of the Company’s capital stock. The vesting and exercise provisions of options or restricted awards granted are determined individually with each grant. Stock options have a 10-year life 2015 Plan The 2015 Equity Incentive Plan (2015 Plan) became effective on July 14, 2015. As of December 31, 2019, 291,191 shares were reserved for issuance under the 2015 Plan. The number of shares reserved for issuance under the 2015 Plan will increase automatically on January 1 of each calendar year 2016 through 2025 by the number of shares equal to 4% of the total outstanding shares of the Company’s common stock as of the immediately preceding December 31. The Company’s Board of Directors or Compensation Committee may reduce the amount of the increase in any particular year. The exercise price of each stock-based award issued under the 2015 Plan is required to be no less than the fair value of the Company’s capital stock. The vesting and exercise provisions of options or restricted awards granted are determined individually with each grant. Stock options have a 10-year life On January 21, 2020 the Company’s stockholders approved the following amendments to the 2015 Plan: (i) increase to the authorized number of shares available for issuance by 4,312,500 shares and proportionately increase the share limit related to incentive stock options, (ii) provide limits on the total value of compensation that may be granted to any non-employee director 2008 Plan The Company granted options under the 2008 Stock Plan (2008 Plan) until July 2015 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2008 Plan. The 2008 Plan provided for the granting of Incentive Stock Options (ISO), nonqualified stock options and stock purchase rights. In connection with the Board of Director’s approval of the 2015 Plan, all remaining shares available for future award under the 2008 Plan were transferred to the 2015 Plan, and the 2008 Plan was terminated. A summary of activity under the 2008 Plan, 2015 Plan and 2018 Plan and related information is as follows: Options Outstanding Shares Number Weighted- Weighted- Aggregate Outstanding—December 31, 2018 48,689 262,539 $ 114.46 7.80 $ 545 Awards authorized under the 2015 Plan 74,365 Options granted (94,820 ) 94,820 66.54 Options exercised — (8,056 ) 55.23 Options forfeited/cancelled 23,280 (23,280 ) 106.43 Outstanding—December 31, 2019 51,514 326,023 $ 102.56 7.45 $ 11 Exercisable—December 31, 2019 199,739 $ 119.96 6.57 $ — Vested and expected to vest—December 31, 2019 326,023 $ 102.56 7.45 $ 11 The weighted-average grant date fair values of options granted during the years ended December 31, 2019, 2018 and 2017 was $50.40, $70.00 and $43.60 per share. The aggregate intrinsic value of options exercised was $0.1 million, $0.2 million and $0.2 million for the years ended December 31, 2019, 2018 and 2017. The total grant date fair value of options vested for the years ended December 31, 2019, 2018 and 2017 was $6.0 million, $5.9 million and $6.5 million. As of December 31, 2019, total unrecognized stock-based compensation related to unvested stock options was $6.0 million, which the Company expects to recognize over a remaining weighted-average period of 2.5 years. 2015 Employee Stock Purchase Plan The Company adopted the 2015 Employee Stock Purchase Plan (ESPP) and initially reserved 17,500 shares of common stock as of its effective date of July 15, 2015. The aggregate number of shares issued over the term of the 2015 Employee Stock Purchase Plan will not exceed 85,000 shares of common stock. The ESPP will not become effective until such time as the Compensation Committee determines in the future, and as of December 31, 2019, the initial offering periods had not commenced. As of December 31, 2019, no shares of common stock have been issued to employees participating in the ESPP and 17,500 shares were available for issuance under the ESPP.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes The geographical breakdown of loss before provision for income taxes is as follows: Year Ended December 31, 2019 2018 2017 (in thousands) United States $ (89,459 ) $ (54,395 ) $ (42,425 ) International 1,024 758 566 Loss before provision for (benefit from) income taxes, net $ (88,435 ) $ (53,637 ) $ (41,859 ) The components of the provision for (benefit from) income taxes are as follows: Year Ended December 31, 2019 2018 2017 (in thousands) Current tax provision (benefit): Federal $ — $ — $ — State — — — Foreign 85 (180 ) 183 Total current tax provision (benefit) 85 (180 ) 183 Deferred tax provision (benefit): Foreign (245 ) (122 ) (27 ) Total deferred tax provision (benefit) $ (245 ) $ (122 ) $ (27 ) Total provision for (benefit from) income taxes $ (160 ) $ (302 ) $ 156 The reconciliation between income taxes computed at the federal statutory income tax rate and the provision for (benefit from) income taxes is as follows: Year Ended December 31, 2019 2018 2017 Federal statutory rate 21.0 % 21.0 % 34.0 % Effect of: Effect of ownership change on deferred tax assets (29.0 ) — (84.8 ) Change in valuation allowance 12.4 (22.2 ) 69.5 Warrant issuance and remeasurement (5.3 ) — — Federal tax credit 1.5 2.4 (0.9 ) State income tax benefit, net of federal benefit 0.2 0.3 0.1 US tax reform deferred impact on tax rate change — — (17.3 ) Other permanent items (0.6 ) (1.0 ) (1.0 ) Total provision for (benefit from) income taxes 0.2 % 0.5 % (0.4 )% On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (Tax Act). The Tax Act significantly revised U.S. tax law by, among other provisions, lowering the U.S. federal statutory income tax rate from 35% to 21%. To account for the rate reduction, the Company recorded a decrease of its net deferred tax assets of $7.2 million for the period ended December 31, 2017. This did not have an impact on the Company’s financial statements since its U.S. deferred tax assets are fully offset by a valuation allowance. The components of the deferred tax assets are as follows: December 31, 2019 2018 (in thousands) Deferred tax assets: 59 (e) expenditures and amortization $ 5,902 $ 1,435 Stock based compensation 4,663 3,642 Net operating loss carryforwards 2,649 18,347 License fee 2,538 2,008 Research and development credits 486 1,137 Other 967 972 Gross deferred tax assets 17,205 27,541 Valuation allowance (16,441 ) (27,317 ) Total deferred tax assets 764 224 Deferred tax liabilities: Lease Asset 244 — Other 90 39 Total deferred tax liabilities 334 39 Total net deferred tax assets $ 430 $ 185 Recognition of deferred tax assets is appropriate when realization of these assets is more likely than not. Based upon the weight of available evidence, which includes historical operating performance and the recorded cumulative net losses in prior fiscal periods, the Company recorded a full valuation allowance of $16.4 million and $27.3 million against the net U.S. deferred tax assets as of December 31, 2019 and 2018. The net valuation allowance de in Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use the existing U.S. deferred tax assets. Based on the weight of all evidence, including a history of operating losses and the Company’s ability to generate future taxable income to realize the assets, management has determined that it is more likely than not that the U.S. deferred tax assets will not be realized. Utilization of the Company’s net operating loss and U.S. research and development credit carryforwards to offset taxable income are subject to an annual limitation, pursuant to Internal Revenue Code (IRC) Sections 382 and 383. As a result of the stock offering that occurred in November 2019 an ownership change under Section 382 is deemed to have occurred. As such, certain of the Company’s tax attributes existing as of the date of the ownership change are not be available for future use. The loss of these attributes does not have any impact on the financial statements since the net U.S. deferred tax assets are offset by a full valuation allowance. As of December 31, 2019, the Company has gross U.S. federal tax net operating loss carryforwards of $1.2 million, $50.7 million expiring in years ranging from 2022 to 2039. $0.1 million which expire in 2039 and net tax credit carryforwards in a foreign jurisdiction of $0.4 million which begin to expire in 2038. Uncertain Tax Positions The activity related to the gross amount of unrecognized tax benefits is as follows: Year Ended December 31, 2019 2018 2017 (in thousands) Beginning balance $ 264 $ 43 $ 311 Increases based on tax positions related to prior years — 109 — Decreases based on tax positions related to prior years (103 ) — (79 ) Decreases due to ownership change — — (232 ) Increases based on tax positions in current year 153 112 43 Settlement — — — Lapse of statute of limitations — — — Ending balance $ 314 $ 264 $ 43 If recognized, gross unrecognized tax benefits would not have a material impact on the Company’s effective tax rate due to the Company’s full valuation allowance position on the U.S. deferred tax assets. From time to time, the Company is subject to review by tax authorities. It is not possible to estimate the impact of changes, if any, to previously recorded uncertain tax positions. However, the Company does not expect the changes, if any, to be materially different from what is recorded and will adjust its estimate and liability as necessary. The Company recognizes interest and penalties related to unrecognized tax benefits in the provision for income taxes in the accompanying consolidated statement of operations. Accrued interest and penalties, if applicable, are included in accrued liabilities in the consolidated balance sheet. For the years ended December 31, 2019 and 2018, the Company did not recognize any accrued interest and penalties. The Company is subject to taxation in the United States, various states, Canada and Australia. Tax years 2016 through 2018 remain open to examination by the United States, various state jurisdictions and Canada. The tax year ended December 31, 2018 remains open to examination in Australia. Other than routine reviews by tax authorities for tax credits claimed, the Company is not under examination in any tax jurisdiction for any year.

Selected Quarterly Financial Da

Selected Quarterly Financial Data	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data	14. Selected Quarterly Financial Data (Unaudited) The following tables present certain selected unaudited consolidated quarterly financial information for each of the eight quarters ended December 31, 2019. This consolidated quarterly information has been prepared on the same basis as the consolidated financial statements and includes all adjustments necessary to state fairly the information for the periods presented. The selected consolidated quarterly financial results from operations for the years ended December 31, 2019 and 2018 are set forth therein. Net loss per share for all periods presented has been retroactively adjusted to reflect the 1-for-40 reverse stock split effected on January 22, 2020 as described in Note 1. Fiscal 2019 Quarter Ended March 31, June 30, September 30, December 31, (2) (in thousands, except per share amounts) Operating expenses $ 13,502 $ 15,207 $ 13,264 $ 25,019 Net loss (1) $ (13,032 ) $ (14,878 ) $ (12,903 ) $ (47,462 ) Basic and diluted net loss per share $ (7.00 ) $ (7.97 ) $ (6.91 ) $ (7.88 ) Fiscal 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Operating expenses $ 11,754 $ 12,963 $ 16,051 $ 14,649 Net loss (1) $ (11,525 ) $ (11,960 ) $ (15,567 ) $ (14,283 ) Basic and diluted net loss per share $ (7.72 ) $ (6.44 ) $ (8.38 ) $ (7.68 ) (1) Net loss from continuing operations and net loss attributable to holders of common stock and preferred stock with characteristics of common stock are the same as net loss for all periods presented. (2) Net loss for the quarter ended December 31, 2019 included a $20.9 million non-cash e non-cash

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP). The accompanying consolidated financial statements include the accounts of Sierra Oncology, Inc. and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the consolidated 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 consolidated financial statements and the reported amounts of expense during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include, but are not limited to the fair value of convertible voting preferred stock, stock options and warrants issued, fair value of the securities issuance obligation, accruals such as research and development costs, and recoverability of the Company’s net deferred tax assets, and related valuation allowance. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates.
Foreign Currency	Foreign Currency The functional currency of the Company’s foreign subsidiaries is the U.S. Dollar. Transactions denominated in currencies other than the functional currency are recorded at prevailing exchange rates during the period. At the end of each reporting period, monetary assets and liabilities are remeasured to the functional currency using exchange rates in effect at the balance sheet date. Non-monetary
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents. Cash and cash equivalents consist primarily of funds invested in readily available checking and savings accounts and highly liquid investments in money market funds.
Restricted Cash	Restricted Cash Restricted cash, which consists of funds invested in a money market fund, represents collateral for a corporate credit card facility and is included in other assets in the accompanying consolidated balance sheets.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that subject the Company to significant concentrations of credit risk consist of cash, cash equivalents and restricted cash. All of the Company’s cash, cash equivalents and restricted cash are held at financial institutions in the United States and Canada that management believes to be of high credit quality. Deposits held in the United States and Canada with these financial institutions exceed federally insured limits. The primary focus of the Company’s investment strategy is to preserve capital and meet liquidity requirements. The Company’s investment policy addresses the level of credit exposure by limiting the concentration in any one corporate issuer and establishing a minimum allowable credit rating.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s cash and cash equivalents, restricted cash, other current assets, accounts payable and accrued liabilities approximate their fair values at December 31, 2019 and 2018, due to their short duration. Prior to its repayment in December 2019, the term loan bore interest at prevailing market rates for instruments with similar characteristics, accordingly, the carrying value of this instrument approximated its fair value. The warrant liabilities and securities issuance obligation contain unobservable inputs that reflect the Company’s own assumptions in which there is little, if any, market activity at the measurement date, thus the Company’s warrant liabilities and securities issuance obligation are measured at their fair values on a recurring basis using unobservable inputs. The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines the fair value of its financial instruments based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels: Level 1 Level 2 Level 3
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net are stated at cost, less accumulated depreciation. Depreciation on property and equipment, excluding leasehold improvements, is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful lives of the assets or the remaining lease term. Depreciation begins at the time the asset is placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations.
Other Assets	Other Assets Other assets consist primarily of restricted cash pledged as collateral for a corporate credit card facility
Operating Lease Right-of-Use Asset and Lease Liabilities	Operating Lease Right-of-Use Asset On January 1, 2019, the Company adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) and non-lease components The Company recognizes an operating lease with terms greater than one year as right-of-use (ROU)
Warrant Liabilities	Warrant Liabilities The Company accounts for its warrants issued in connection with its November 2019 financing based upon the characteristics and provisions of the instruments. Warrants classified as derivative liabilities are recorded on the Company’s consolidated balance sheets at their fair value on the date of issuance and remeasured to fair value on each subsequent reporting period, with the changes in fair value recognized as a component of other income (expense), net in the accompanying consolidated statements of operations. The Company will continue to adjust the carrying value of the warrants until such time as the warrants are no longer considered derivative instruments, or until the earlier of the exercise of the warrants or the expiration of the warrants, at which time the liabilities will be reclassified to additional paid-in non-marketable Securities Issuance Obligation The Company recognizes its securities issuance obligation pursuant to the amendment to the Asset Purchase Agreement with Gilead Sciences, Inc. (Gilead) at their fair values on the date such obligations arose. At the end of each reporting period, changes in estimated fair values during the period are recognized as research and development costs in the accompanying consolidated statements of operations. The Company will continue to adjust the fair values of the obligations until the securities are issued, at which time the liabilities will be reclassified to common stock and additional paid-in non-marketable non-marketable
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. The Company accounts for non-refundable Upfront payments made in connection with license and asset purchase agreements are expensed as research and developments costs, as the assets acquired do not have alternative future use. Contingent milestone payment obligations due to third parties under license and asset purchase agreements are expensed when the milestones are considered probable of occurring. To the extent an obligation is to be settled by future issuance of securities, the fair value of these instruments is recorded in research and development expense until the securities are issued. Research and development costs include fees incurred in connection with license and asset purchase agreements and their related amendments, compensation and other related costs for employees engaged in research and development, costs associated with research and preclinical studies, clinical trials, regulatory activities, manufacturing activities to support clinical activities, fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company and an allocation of overhead expenses.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based payments at fair value, which is measured using the Black-Scholes option-pricing model. For stock-based awards that vest subject to the satisfaction of a service requirement, the fair value measurement date for stock-based compensation awards is the date of grant and the expense is recognized on a straight-line basis over the vesting period, which is generally the service period. The Company accounts for forfeitures as they occur. On January 1, 2019, the Company adopted FASB ASU No. 2018-07 , Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting,
Income Taxes	Income Taxes The Company uses the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Management makes an assessment of the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s historical operating performance and the recorded cumulative net losses in prior fiscal periods, the net U.S. deferred tax assets have been offset by a full valuation allowance. The Company recognizes uncertain income tax positions at the largest amount that is more likely than not to be sustained upon audit by the relevant taxing authority. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained. Changes in recognition or measurement are reflected in the period in which judgment occurs. The Company recognizes interest and penalties related to the underpayment of income taxes as a component of provision for (benefit from) income taxes, net.
Segment Information	Segment Information Operating segments are components of an enterprise for which separate financial information is available and is evaluated regularly by the Company’s chief operating decision maker in deciding how to allocate resources and assessing performance. The Company’s chief operating decision maker is its Chief Executive Officer. The Company’s Chief Executive Officer views the Company’s operations and manages its business in one

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Schedule of Outstanding Shares of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share	The following shares of common stock equivalents were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been antidilutive: As of December 31, 2019 2018 2017 Series A warrants for common stock 7,802,241 — — Series B warrants for common stock 2,574,727 — — Stock options to purchase common stock 326,023 262,539 186,710 Warrant for common stock 1,839 1,839 — Total potential dilutive shares 10,704,830 264,378 186,710

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of Fair Value Assets And Liabilities Measured On Recurring Basis	The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy: December 31, 2019 Level 1 Level 2 Level 3 Total (in thousands) Financial Assets Money market funds $ 146,240 $ — $ — $ 146,240 Restricted money market funds 300 — — 300 Total financial assets $ 146,540 $ — $ — $ 146,540 Financial Liabilities Warrant liabilities $ — $ — $ 45,935 $ 45,935 Securities issuance obligation — — 10,485 10,485 Total financial liabilities $ — $ — $ 56,420 $ 56,420 December 31, 2018 Level 1 Level 2 Level 3 Total (in thousands) Financial Assets Money market funds $ 105,224 $ — $ — $ 105,224 Restricted money market funds 300 — — 300 Total financial assets $ 105,524 $ — $ — $ 105,524
Schedule of Fair Value Measurement Inputs and Valuation Techniques	At November 13, 2019, the Company estimated the fair values of the financial liabilities using the following assumptions: Series A Warrant Series B Warrant Warrant Issuance Common Stock Expected term (in years) 5.2 2.3 5.2 N/A Expected volatility 43 % 88 % 43 % N/A Risk-free interest rate 1.70 % 1.64 % 1.70 % N/A Expected dividend yield — % — % — % N/A Discount for lack of marketability 30 % 30 % 32 % 32 % At December 31, 2019, the Company remeasured these liabilities to their fair values using the following assumptions: Series A Warrant Series B Warrant Warrant Issuance Common Stock Expected term (in years) 5.1 2.2 5.1 N/A Expected volatility 43 % 88 % 43 % N/A Risk-free interest rate 1.69 % 1.59 % 1.70 % N/A Expected dividend yield — % — % — % N/A Discount for lack of marketability 25 % 25 % 25 % 25 %
Schedule of Financial Liabilitites Fair Value of Recurring Basis Using Unobservable Inputs	The following table provides a summary of changes in the estimated fair values of the Company’s Level 3 financial liabilities, which are measured at fair value on a recurring basis using unobservable inputs: Series A Warrant Series B Warrant Warrant Issuance Common Stock Total (in thousands) Balance, December 31, 2018 $ — $ — $ — $ — $ — Issuance of warrants 17,133 7,876 — — 25,009 Securities issuance obligation 1,543 4,903 6,446 Changes in fair value 15,483 5,443 1,493 2,546 24,965 Balance, December 31, 2019 $ 32,616 $ 13,319 $ 3,036 $ 7,449 $ 56,420

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Cash and Cash Equivalents	Cash and cash equivalents consist of the following: December 31, 2019 2018 (in thousands) Cash $ 1,288 $ 822 Cash equivalents: Money market accounts 146,240 105,224 Total cash and cash equivalents $ 147,528 $ 106,046
Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported in the consolidated balance sheets to the amounts shown in the consolidated statements of cash flows. December 31, 2019 December 31, (in thousands) Cash and cash equivalents $ 147,528 $ 106,046 Restricted cash included in other assets 300 300 Total cash, cash equivalents and restricted cash shown in the consolidated statement of cash flows $ 147,828 $ 106,346
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following: December 31, 2019 2018 (in thousands) Prepaid insurance $ 918 $ 555 Prepaid research and development project costs 853 762 Other receivables 190 751 Income taxes receivable 7 163 Other 401 475 Total prepaid expenses and other current assets $ 2,369 $ 2,706
Summary of Property and Equipment, Net	Property and equipment, net consists of the following: December 31, 2019 2018 (in thousands) Software $ 352 $ 325 Leasehold improvements 112 112 Computer equipment 89 89 Furniture and fixtures 3 3 Property and equipment, gross 556 529 Less: accumulated depreciation (443 ) (361 ) Total property and equipment, net $ 113 $ 168
Summary of Accrued and Other Liabilities	Accrued liabilities consist of the following: December 31, 2019 2018 (in thousands) Accrued employee related costs $ 3,420 $ 3,223 Accrued research and development costs 2,668 4,485 Accrued professional fees 817 357 Operating lease liability 187 — Other 78 747 Total accrued liabilities $ 7,170 $ 8,812

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Schedule of Components of Lease Expense and Related Cash Flows	The components of lease expense and related cash flows for the year ended December 31, 2019 were as follows: Year Ended December 31, 2019 Operating lease cost $ 203 Short-term lease cost 117 320 Operating cash flows used for operating leases $ 198
Schedule of Maturities Lease Liabilities under Leases Agreement	As of December 31, 2019, maturities of lease liability due under the lease agreement are as follows: Years Ending December 31: Operating (in thousands) 2020 217 2021 221 2022 177 Total lease payments 615 Less imputed interest (54 ) Total $ 561

Common Stock Reserved for Iss_2

Common Stock Reserved for Issuance (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of Common Stock Reserved for Issuance	The Company is required to reserve and keep available out of its authorized but unissued shares of common stock a number of shares sufficient to effect the conversion of all outstanding preferred stock, options granted and available for grant under the incentive plans, shares reserved for issuance under the employee stock purchase plan and issued warrant. December 31, 2019 2018 Shares reserved for conversion of Series A Preferred Stock 7,803,273 — Shares reserved under Series A warrant 7,802,241 — Shares reserved under Series B warrant 2,574,727 — Outstanding stock options under equity incentive plans 326,023 262,539 Shares reserved for future option grants under equity plans 51,514 48,689 Shares reserved under the 2015 employee stock purchase plan 17,500 17,500 Shares reserved under warrant upon contingent events — 3,677 Outstanding warrant 1,839 1,839 Total common stock reserved for issuance 18,577,117 334,244

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Schedule of Stock-based Compensation Expense for Employees and Non-employees	In the accompanying consolidated statement of operations, the Company recognized stock-based compensation expense for its employees and non-employees Year Ended December 31, 2019 2018 2017 (in thousands) Research and development $ 3,873 $ 4,499 $ 3,966 General and administrative 1,822 2,297 1,939 Total stock-based compensation $ 5,695 $ 6,796 $ 5,905
Schedule of Estimated Grant-date Fair Value of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions	The estimated grant-date fair value of all the Company’s stock-based awards was calculated using the Black-Scholes option pricing model, based on the following assumptions: Year Ended December 31, 2019 2018 2017 Expected term (in years) 5.3 – 6.9 5.3 – 7.0 5.3 – 7.0 Expected volatility 89 – 94 % 88 – 91 % 86 – 96 % Risk-free interest rate 1.6 – 2.6 % 2.6 – 3.1 % 1.8 – 2.3 % Expected dividend rate — % — % — %
Summary of Stock-Based Compensation Activity	A summary of activity under the 2008 Plan, 2015 Plan and 2018 Plan and related information is as follows: Options Outstanding Shares Number Weighted- Weighted- Aggregate Outstanding—December 31, 2018 48,689 262,539 $ 114.46 7.80 $ 545 Awards authorized under the 2015 Plan 74,365 Options granted (94,820 ) 94,820 66.54 Options exercised — (8,056 ) 55.23 Options forfeited/cancelled 23,280 (23,280 ) 106.43 Outstanding—December 31, 2019 51,514 326,023 $ 102.56 7.45 $ 11 Exercisable—December 31, 2019 199,739 $ 119.96 6.57 $ — Vested and expected to vest—December 31, 2019 326,023 $ 102.56 7.45 $ 11

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Schedule of Geographical Breakdown of Loss Before Provision for Income Taxes	The geographical breakdown of loss before provision for income taxes is as follows: Year Ended December 31, 2019 2018 2017 (in thousands) United States $ (89,459 ) $ (54,395 ) $ (42,425 ) International 1,024 758 566 Loss before provision for (benefit from) income taxes, net $ (88,435 ) $ (53,637 ) $ (41,859 )
Components of Provision (Benefit from) for Income Taxes	The components of the provision for (benefit from) income taxes are as follows: Year Ended December 31, 2019 2018 2017 (in thousands) Current tax provision (benefit): Federal $ — $ — $ — State — — — Foreign 85 (180 ) 183 Total current tax provision (benefit) 85 (180 ) 183 Deferred tax provision (benefit): Foreign (245 ) (122 ) (27 ) Total deferred tax provision (benefit) $ (245 ) $ (122 ) $ (27 ) Total provision for (benefit from) income taxes $ (160 ) $ (302 ) $ 156
Reconciliation Between Income Taxes Computed at the Federal Statutory Income Tax Rate and the Provision for Income Taxes	The reconciliation between income taxes computed at the federal statutory income tax rate and the provision for (benefit from) income taxes is as follows: Year Ended December 31, 2019 2018 2017 Federal statutory rate 21.0 % 21.0 % 34.0 % Effect of: Effect of ownership change on deferred tax assets (29.0 ) — (84.8 ) Change in valuation allowance 12.4 (22.2 ) 69.5 Warrant issuance and remeasurement (5.3 ) — — Federal tax credit 1.5 2.4 (0.9 ) State income tax benefit, net of federal benefit 0.2 0.3 0.1 US tax reform deferred impact on tax rate change — — (17.3 ) Other permanent items (0.6 ) (1.0 ) (1.0 ) Total provision for (benefit from) income taxes 0.2 % 0.5 % (0.4 )%
Components of the Deferred Tax Assets	The components of the deferred tax assets are as follows: December 31, 2019 2018 (in thousands) Deferred tax assets: 59 (e) expenditures and amortization $ 5,902 $ 1,435 Stock based compensation 4,663 3,642 Net operating loss carryforwards 2,649 18,347 License fee 2,538 2,008 Research and development credits 486 1,137 Other 967 972 Gross deferred tax assets 17,205 27,541 Valuation allowance (16,441 ) (27,317 ) Total deferred tax assets 764 224 Deferred tax liabilities: Lease Asset 244 — Other 90 39 Total deferred tax liabilities 334 39 Total net deferred tax assets $ 430 $ 185
Unrecognized Tax Benefits	The activity related to the gross amount of unrecognized tax benefits is as follows: Year Ended December 31, 2019 2018 2017 (in thousands) Beginning balance $ 264 $ 43 $ 311 Increases based on tax positions related to prior years — 109 — Decreases based on tax positions related to prior years (103 ) — (79 ) Decreases due to ownership change — — (232 ) Increases based on tax positions in current year 153 112 43 Settlement — — — Lapse of statute of limitations — — — Ending balance $ 314 $ 264 $ 43

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Summary of Selected Unaudited Consolidated Quarterly Financial Information	Fiscal 2019 Quarter Ended March 31, June 30, September 30, December 31, (2) (in thousands, except per share amounts) Operating expenses $ 13,502 $ 15,207 $ 13,264 $ 25,019 Net loss (1) $ (13,032 ) $ (14,878 ) $ (12,903 ) $ (47,462 ) Basic and diluted net loss per share $ (7.00 ) $ (7.97 ) $ (6.91 ) $ (7.88 ) Fiscal 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Operating expenses $ 11,754 $ 12,963 $ 16,051 $ 14,649 Net loss (1) $ (11,525 ) $ (11,960 ) $ (15,567 ) $ (14,283 ) Basic and diluted net loss per share $ (7.72 ) $ (6.44 ) $ (8.38 ) $ (7.68 ) (1) Net loss from continuing operations and net loss attributable to holders of common stock and preferred stock with characteristics of common stock are the same as net loss for all periods presented. (2) Net loss for the quarter ended December 31, 2019 included a $20.9 million non-cash e non-cash

The Company and Basis of Pres_2

The Company and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jan. 22, 2020	Mar. 06, 2018	Feb. 21, 2017	Feb. 14, 2017	Dec. 31, 2019	Jan. 29, 2020	Nov. 13, 2019	Dec. 31, 2018
Cash and cash equivalents					$ 147,528			$ 106,046
Subsequent Event [Member]
Description of reverse stock split	1-for-40
Follow on Offering [Member]
Share issued price per share		$ 90		$ 54
Stock issued, shares		546,250	58,690	487,500
Proceeds from issuance of common stock, net of deferred financing costs		$ 46,000		$ 27,400
Underwriting discounts and commissions and offering expenses		$ 3,200		$ 2,100
Convertible preferred stock issued, shares		546,250	58,690	487,500
Series A Warrants [Member] | Underwritten Public Offering [Member]
Number of securitites called by warrants and rights					7,802,241
Excercise price of warrants or rights					$ 13.20
Series B Warrants [Member] | Underwritten Public Offering [Member]
Number of securitites called by warrants and rights					2,574,727
Excercise price of warrants or rights					$ 13.20
Series A Convertible Preferred Stock [Member] | Subsequent Event [Member]
Preferred Stock converted into of the Company's common stock						7,803,273
Series A Convertible Preferred Stock [Member] | Underwritten Public Offering [Member]
Stock issued, shares					103,000
Preferred Stock converted into of the Company's common stock							7,803,273
Convertible preferred stock issued, shares					103,000
Convertible Preferred Stock And Warrants [Member] | Underwritten Public Offering [Member]
Share issued price per share							$ 1,000
Proceeds from issuance of convertible preferred stock and warrants net of issuance cost					$ 97,700
Stock issuance costs					$ 5,300

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019Segment
Summary Of Significant Accounting Policy [Line Items]
Number of operating segment	1
Minimum [Member] | Property Plant and Equipment Other than Leasehold Improvement [Member]
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets	3 years
Maximum [Member] | Property Plant and Equipment Other than Leasehold Improvement [Member]
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets	5 years

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Outstanding Shares of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	10,704,830	264,378	186,710
Series A Warrants For Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	7,802,241
Series B Warrants For Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	2,574,727
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	326,023	262,539	186,710
Warrants for Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	1,839	1,839

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value of Financial Assets Measured on Recurring Basis (Detail) - Fair Value Measurements Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial Assets
Total financial assets	$ 146,540	$ 105,524
Financial Liabilities
Total financial liabilities	56,420
Warrant liabilities [Member]
Financial Liabilities
Total financial liabilities	45,935
Securities issuance obligation [Member]
Financial Liabilities
Total financial liabilities	10,485
Money Market Funds [Member]
Financial Assets
Total financial assets	146,240	105,224
Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	300	300
Level 1 [Member]
Financial Assets
Total financial assets	146,540	105,524
Level 1 [Member] | Money Market Funds [Member]
Financial Assets
Total financial assets	146,240	105,224
Level 1 [Member] | Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	300	$ 300
Level 3 [Member]
Financial Liabilities
Total financial liabilities	56,420
Level 3 [Member] | Warrant liabilities [Member]
Financial Liabilities
Total financial liabilities	45,935
Level 3 [Member] | Securities issuance obligation [Member]
Financial Liabilities
Total financial liabilities	$ 10,485

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Fair Value of Financial Liabilities Assumptions (Detail)	Dec. 31, 2019yr	Nov. 13, 2019yr
Series A Warrant [Member] | Expected term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	5.1	5.2
Series A Warrant [Member] | Expected volatility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.43	0.43
Series A Warrant [Member] | Risk-free interest rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.0169	0.0170
Series A Warrant [Member] | Discount for lack of marketability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.25	0.30
Series B Warrant [Member] | Expected term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	2.2	2.3
Series B Warrant [Member] | Expected volatility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.88	0.88
Series B Warrant [Member] | Risk-free interest rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.0159	0.0164
Series B Warrant [Member] | Discount for lack of marketability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.25	0.30
Warrent Issuance Obligation [Member] | Expected term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	5.1	5.2
Warrent Issuance Obligation [Member] | Expected volatility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.43	0.43
Warrent Issuance Obligation [Member] | Risk-free interest rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.0170	0.0170
Warrent Issuance Obligation [Member] | Discount for lack of marketability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.25	0.32
Common stock Issuance Obligation [Member] | Discount for lack of marketability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.25	0.32

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Changes in Fair Values Level Financial Liabilities Recurring Basis Using Unobservable Inputs (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of warrants	$ 25,000
Changes in fair value	20,926
Fair Value Measurements Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of warrants	25,009
Securities issuance obligation	6,446
Changes in fair value	24,965
Ending Balance	56,420
Fair Value Measurements Recurring [Member] | Series A Warrant [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of warrants	17,133
Changes in fair value	15,483
Ending Balance	32,616
Fair Value Measurements Recurring [Member] | Series B Warrant [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of warrants	7,876
Changes in fair value	5,443
Ending Balance	13,319
Fair Value Measurements Recurring [Member] | Warrent Issuance Obligation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities issuance obligation	1,543
Changes in fair value	1,493
Ending Balance	3,036
Fair Value Measurements Recurring [Member] | Common stock Issuance Obligation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities issuance obligation	4,903
Changes in fair value	2,546
Ending Balance	$ 7,449

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash	$ 1,288	$ 822
Cash equivalents:
Money market accounts	146,240	105,224
Total cash and cash equivalents	$ 147,528	$ 106,046

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 147,528	$ 106,046
Restricted cash included in other assets	300	300
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows	$ 147,828	$ 106,346	$ 100,536	$ 109,207

Balance Sheet Components - Su_3

Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid insurance	$ 918	$ 555
Prepaid research and development project costs	853	762
Other receivables	190	751
Income taxes receivable	7	163
Other	401	475
Total prepaid expenses and other current assets	$ 2,369	$ 2,706

Balance Sheet Components - Su_4

Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 556	$ 529
Less: accumulated depreciation	(443)	(361)
Total property and equipment, net	113	168
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	352	325
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	112	112
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	89	89
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3	$ 3

Balance Sheet Components - Su_5

Balance Sheet Components - Summary of Accrued and Other Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued employee related costs	$ 3,420	$ 3,223
Accrued research and development costs	2,668	4,485
Accrued professional fees	817	357
Operating lease liability	187
Other	78	747
Total accrued and other liabilities	$ 7,170	$ 8,812

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation	$ 0.1	$ 0.1	$ 0.3

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Loss Contingencies [Line Items]
Operating lease right-of-use asset	$ 589			$ 800
Operating lease liability	$ 615			$ 700
Rent expense		$ 500	$ 500
Weighted-average remaining lease term, operating lease (Year)	3 years 2 months 12 days
Weighted-average discount rate, Operating lease	6.50%
Operating Lease Agreement To Lease Office Space [Member] | San Francisco [Member]
Loss Contingencies [Line Items]
Operating lease agreement expiration date	Apr. 30, 2019
Vancouver Lease [Member] | Vancouver [Member]
Loss Contingencies [Line Items]
Operating lease agreement expiration date	Feb. 28, 2023
Additional lease term to be extended	5 years

Leases - Schedule of Components

Leases - Schedule of Components of Lease Expense and Related Cash Flows (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 203
Short-term lease cost	117
Total Lease Cost	320
Operating cash flows used for operating leases	$ 198

Leases - Schedule of Maturities

Leases - Schedule of Maturities Lease Liabilities under Leases Agreement (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Leases [Abstract]
2020	$ 217
2021	221
2022	177
Total lease payments	615	$ 700
Less imputed interest	(54)
Total	$ 561

Term Loan - Additional Informat

Term Loan - Additional Information (Detail) - Silicon Valley Bank [Member]	Dec. 18, 2019USD ($)	Aug. 31, 2018USD ($)Tranches	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)
Term Loans [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loans		$ 15,000,000
Number of tranches | Tranches		3
Loan agreement, description			Contemporaneously with executing the Loan Agreement, the Company drew down the first $5.0 million tranche.
Loan agreement, frequency of payments			monthly
Interest expense			$ 900,000	$ 200,000
Term loan repaid	$ 300,000
Repayment of term loan	5,000,000
Term Loans [Member] | Tranche One [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loans				$ 5,000,000
Amount borrowed			$ 5,000,000
Amortization of debt discount and accretion of final payment	$ 100,000
Warrants to Purchase Common Stock [Member]
Debt Instrument [Line Items]
Warrant expiration date		Aug. 21, 2028
Warrants to Purchase Common Stock [Member] | Term Loans [Member]
Debt Instrument [Line Items]
Warrants issued in connection with loan | shares			1,839
Excercise price of warrants or rights | $ / shares			$ 74.80

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ / shares in Units, $ in Millions	Jan. 31, 2020shares	Jan. 01, 2020$ / sharesshares	Aug. 31, 2018USD ($)	Oct. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2019USD ($)Payments	Jan. 31, 2017USD ($)
Carna License Agreement [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment						$ 270
Milestone payment						$ 4
Upfront payment paid					$ 0.9
Number of milestone payments recorded | Payments						0
CPF License Agreements [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment						$ 19.5
Milestone payment							$ 2
Upfront payment paid				$ 7
Additional milestone payment payable						319.5
CPF License Agreements [Member] | Phase One Clinical Trial [Member]
Loss Contingencies [Line Items]
Milestone payment						7.5
CPF License Agreements [Member] | Phase Two Clinical Trial [Member]
Loss Contingencies [Line Items]
Milestone payment						12
Asset Purchase Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid			$ 3
Aggregate milestone payment						190
Expense included research and development cost						6.5
Additional Exepense included Research and development cost						$ 4
Asset Purchase Agreement [Member] | Gilead [Member] | Subsequent Event [Member]
Loss Contingencies [Line Items]
Stock issued, shares | shares	725,283
Number of securitites called by warrants and rights | shares	725,283
Asset Purchase Agreement Amendment [Member] | Gilead [Member] | Subsequent Event [Member]
Loss Contingencies [Line Items]
Stock issued, shares | shares		725,283
Number of securitites called by warrants and rights | shares		725,283
Excercise price of warrants or rights | $ / shares		$ 13.20

Common Stock Reserved for Iss_3

Common Stock Reserved for Issuance - Schedule of Common Stock Reserved for Issuance (Detail) - shares	Dec. 31, 2019	Dec. 31, 2018	Jul. 15, 2015
Class of Stock [Line Items]
Total common stock reserved for future issuance	18,577,117	334,244
Series A Warrant [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance	7,802,241
Series B Warrant [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance	2,574,727
Equity Incentive Plans [Member]
Class of Stock [Line Items]
Awards outstanding	326,023	262,539
Total common stock reserved for future issuance	51,514	48,689
2015 Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance	17,500	17,500	17,500
Warrants to Purchase Common Stock [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance		3,677
Outstanding warrant	1,839	1,839
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance	7,803,273

Common Stock Reserved for Iss_4

Common Stock Reserved for Issuance - Additional Information (Detail) - Subsequent Event [Member] - shares	Jan. 31, 2020	Jan. 21, 2020
Class of Stock [Line Items]
Increase Decrease Authorized Shares Available For Issuance		4,312,500
Gilead [Member] | Asset Purchase Agreement [Member]
Class of Stock [Line Items]
Stock issued, shares	725,283
Number of Securities called by warrants and rights, shares	725,283
2015 Equity Incentive Plan [Member]
Class of Stock [Line Items]
Increase Decrease Authorized Shares Available For Issuance		4,312,500

Preferred Stock - Additional in

Preferred Stock - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions	Nov. 13, 2019	Dec. 31, 2019	Jan. 29, 2020	Dec. 31, 2018
Series A Convertible Voting Preferred Stock [Member]
Preferred stock, shares authorized		10,000,000		10,000,000
Preferred stock, par value		$ 0.001		$ 0.001
Preferred stock, shares issued		103,000		0
Preferred stock, shares outstanding		103,000		0
Stock issued, shares	103,000
Preferred stock voting rights		The Series A Preferred Stock will initially vote together with the Company’s common stock on an as-converted basis. Holders of each Series A Preferred Stock will be entitled to one vote for each share of common stock into which their Series A Preferred Stock is then-convertible. Following the date the Series A Preferred Stock automatically converts into shares of the Company’s common stock, except otherwise required by law, the Series A Preferred Stock will have no voting rights.
Series A Convertible Voting Preferred Stock [Member] | Subsequent Event [Member]
Preferred Stock converted into of the Company's common stock			7,803,273
Convertible Preferred Stock And Warrants And Underwritten Follow On Offering [Member]
Share issued price per share	$ 1,000
Proceeds from issuance of convertible preferred stock and warrants net of issuance cost	$ 97.7
Series A Preferred Stock [Member]
Share issued price per share		$ 1,000
Preferred stock conversion price per share		$ 13.20

Warrant Liabilities - Additiona

Warrant Liabilities - Additional information (Detail) $ / shares in Units, $ in Thousands	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
Class of Warrant or Right [Line Items]
Fair value of warrants estimate	$ 45,900	$ 45,900
Non-cash expense on warrant liability		20,926
Issuance of warrants		$ 25,000
Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants and rights outstanding term	5 years	5 years
Series B Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants and rights outstanding term	75 days	75 days
Exercise of Future Warrants Value	$ 34,000
Underwritten Follow On Offerings [Member] | Series A Warrants [Member]
Class of Warrant or Right [Line Items]
Number of securitites called by warrants and rights | shares	7,802,241	7,802,241
Excercise price of warrants or rights | $ / shares	$ 13.20	$ 13.20
Underwritten Follow On Offerings [Member] | Series B Warrants [Member]
Class of Warrant or Right [Line Items]
Number of securitites called by warrants and rights | shares	2,574,727	2,574,727
Excercise price of warrants or rights | $ / shares	$ 13.20	$ 13.20

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock-based Compensation Expense for Employees and Non-employees (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 5,695	$ 6,796	$ 5,905
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	3,873	4,499	3,966
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 1,822	$ 2,297	$ 1,939

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Estimated Grant-date Fair Values of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, Minimum	89.00%	88.00%	86.00%
Expected volatility, Maximum	94.00%	91.00%	96.00%
Risk-free interest rate, Minimum	1.60%	2.60%	1.80%
Risk-free interest rate, Maximum	2.60%	3.10%	2.30%
Expected dividend yield	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 3 months 18 days	5 years 3 months 18 days	5 years 3 months 18 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 10 months 24 days	7 years	7 years

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Jan. 21, 2020	Jul. 15, 2015	Jul. 14, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance				18,577,117	334,244
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares authorized to be issued during the period	4,312,500
2015 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance		17,500		17,500	17,500
Stock option grants description				The number of shares initially reserved for issuance under the ESPP will increase automatically on January 1 for nine years from the first offering date by the number of shares equal to 1% of the total outstanding shares of the Company's common stock as of the immediately preceding December 31
Common shares authorized to be issued during the period		85,000
Number of common stock issued		0
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance				291,191
Stock option life in years				10 years
Stock option grants description				The number of shares reserved for issuance under the 2015 Plan will increase automatically on January 1 of each calendar year from 2016 through 2025 by the number of shares equal to 4% of the total outstanding shares of the Company's common stock as of the immediately preceding December 31
Percentage threshold of outstanding shares increased annually under the plan			4.00%
Common shares authorized to be issued during the period				74,365
2008 Plan, 2015 Plan and 2018 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards issued				94,820
Awards outstanding				326,023	262,539
Weighted-average grant date fair values of options granted				$ 50.40	$ 70	$ 43.60
Aggregate intrinsic value of options exercised				$ 0.1	$ 0.2	$ 0.2
Total grant date fair value of options vested				6	$ 5.9	$ 6.5
Total unrecognized stock-based compensation related to unvested stock options				$ 6
Weighted-average period				2 years 6 months
2018 Equity Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance				37,500
Stock option life in years				10 years
Awards issued				0
Awards outstanding				0

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
2008 Plan, 2015 Plan and 2018 Plan [Member]
Options Outstanding, Shares Available for Grant
Shares Available for Grant, Beginning balance	48,689
Shares Available for Grant, Granted	(94,820)
Shares Available for Grant, Exercised	0
Shares Available for Grant, forfeited/cancelled	23,280
Shares Available for Grant, Ending balance	51,514	48,689
Options Outstanding, Number of Shares Outstanding
Number of Shares Outstanding, Beginning balance	262,539
Number of Shares Outstanding, Options granted	94,820
Number of Shares Outstanding, Options exercised	(8,056)
Number of Shares Outstanding, Options forfeited/cancelled	(23,280)
Number of Shares Outstanding, Ending balance	326,023	262,539
Number of Shares Outstanding, Exercisable	199,739
Number of Shares Outstanding, Vested and expected to vest	326,023
Options Outstanding, Weighted-Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Beginning balance	$ 114.46
Weighted-Average Exercise Price Per Share, Options granted	66.54
Weighted-Average Exercise Price Per Share, Options exercised	55.23
Weighted-Average Exercise Price Per Share, Options forfeited/cancelled	106.43
Weighted-Average Exercise Price Per Share, Ending balance	102.56	$ 114.46
Weighted-Average Exercise Price Per Share, Exercisable	119.96
Weighted-Average Exercise Price Per Share, Vested and expected to vest	$ 102.56
Options Outstanding, Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years)	7 years 5 months 12 days	7 years 9 months 18 days
Weighted-Average Remaining Contractual Term (Year), Exercisable	6 years 6 months 25 days
Weighted-Average Remaining Contractual Term (Year), Vested and expected to vest	7 years 5 months 12 days
Options Outstanding, Aggregate Intrinsic Value of Outstanding Options
Aggregate Intrinsic Value of Outstanding Options	$ 11	$ 545
Aggregate Intrinsic Value of Outstanding Options, Exercisable	0
Aggregate Intrinsic Value of Outstanding Options, Vested and expected to vest	$ 11
2015 Equity Incentive Plan [Member]
Options Outstanding, Shares Available for Grant
Shares Available for Grant, Awards authorized	74,365

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Federal statutory rate	35.00%	21.00%	21.00%	34.00%
Decrease of net deferred tax assets				$ 7,200,000
Deferred tax assets, valuation allowance		$ 16,441,000	$ 27,317,000
Deferred tax assets, valuation allowance, change in amount		10,900,000	11,900,000
Operating loss carry forwards		1,200,000
Tax credit carry forwards		$ 100,000
Tax credit carry forwards, year begin to expiration		2039
Unrecognized tax benefits, accrued interest and penalties		$ 0	$ 0
Domestic Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carry forwards		$ 50,700,000
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Operating loss carry forwards, expiry year start		2022
Operating loss carry forwards, expiry year end		2039
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Tax credit carry forwards		$ 400,000
Tax credit carry forwards, year begin to expiration		2038
Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Open Tax Year		2016
Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Open Tax Year		2018

Income Taxes - Schedule of Geog

Income Taxes - Schedule of Geographical Breakdown of Loss Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
United States	$ (89,459)	$ (54,395)	$ (42,425)
International	1,024	758	566
Loss before provision for (benefit from) income taxes, net	$ (88,435)	$ (53,637)	$ (41,859)

Income Taxes - Components of Pr

Income Taxes - Components of Provision for (Benefit from) Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current tax provision (benefit):
Federal	$ 0	$ 0	$ 0
State	0	0	0
Foreign	85	(180)	183
Total current tax provision (benefit)	85	(180)	183
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Foreign	(245)	(122)	(27)
Total deferred tax provision (benefit)	(245)	(122)	(27)
Total provision for (benefit from) income taxes	$ (160)	$ (302)	$ 156

Income Taxes - Reconciliation B

Income Taxes - Reconciliation Between Income Taxes Computed at the Federal Statutory Income Tax Rate and the Provision for Income Taxes (Detail)	Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory rate	35.00%	21.00%	21.00%	34.00%
Effect of ownership change on deferred tax assets		(29.00%)		(84.80%)
Change in valuation allowance		12.40%	(22.20%)	69.50%
Warrant issuance and remeasurement		(5.30%)
Federal tax credit		1.50%	2.40%	(0.90%)
State income tax benefit, net of federal benefit		0.20%	0.30%	0.10%
US tax reform deferred impact on tax rate change				(17.30%)
Other permanent items		(0.60%)	(1.00%)	(1.00%)
Total provision for (benefit from) income taxes		0.20%	0.50%	(0.40%)

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
59 (e) expenditures and amortization	$ 5,902	$ 1,435
Stock based compensation	4,663	3,642
Net operating loss carryforwards	2,649	18,347
License fee	2,538	2,008
Research and development credits	486	1,137
Other	967	972
Gross deferred tax assets	17,205	27,541
Valuation allowance	(16,441)	(27,317)
Total deferred tax assets	764	224
Deferred tax liabilities:
Lease Asset	244
Other	90	39
Total deferred tax liabilities	334	39
Total net deferred tax assets	$ 430	$ 185

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Beginning balance	$ 264	$ 43	$ 311
Increases based on tax positions related to prior years		109
Decreases based on tax positions related to prior years	(103)		(79)
Decreases due to ownership change			(232)
Increases based on tax positions in current year	153	112	43
Settlement	0	0	0
Lapse of statute of limitations	0	0	0
Ending balance	$ 314	$ 264	$ 43

Selected Quarterly Financial _3

Selected Quarterly Financial Data - Summary of Selected Unaudited Consolidated Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Operating expenses	$ 25,019	$ 13,264	$ 15,207	$ 13,502	$ 14,649	$ 16,051	$ 12,963	$ 11,754	$ 66,992	$ 55,417	$ 42,619
Net loss	$ (47,462)	$ (12,903)	$ (14,878)	$ (13,032)	$ (14,283)	$ (15,567)	$ (11,960)	$ (11,525)	$ (88,275)	$ (53,335)	$ (42,015)
Basic and diluted net loss per share	$ (7.88)	$ (6.91)	$ (7.97)	$ (7)	$ (7.68)	$ (8.38)	$ (6.44)	$ (7.72)	$ (30.30)	$ (30.16)	$ (33.68)

Selected Quarterly Financial _4

Selected Quarterly Financial Data - Additional Information (Detail) - USD ($) $ in Thousands	Jan. 22, 2020	Dec. 31, 2019
Change in fair value of warrant liability		$ 20,926
Exepense included Research and development cost		$ 10,485
Subsequent Event [Member]
Description of reverse stock split	1-for-40