Stockholders' equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands					12 Months Ended
	Dec. 20, 2019	Dec. 17, 2019	Nov. 12, 2019	Aug. 08, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total number of shares authorized					100,000,000
Common stock, shares authorized			100,000,000		100,000,000	50,000,000
Common stock, par value					$ 0.000001	$ 0.000001
Preferred stock, shares authorized					5,000,000	5,000,000
Preferred stock, par value					$ 0.000001	$ 0.000001
Common stock, shares issued					37,996,849	23,537,368
Common stock, shares outstanding					37,996,849	23,537,368
Preferred stock, shares issued					0	0
Preferred stock, shares outstanding					0	0
Shares of common stock reserved for issuance description					Additionally, the number of shares of common stock reserved for issuance under the 2014 Plan will automatically increase on January 1 of each year for a period of up to 10 years, beginning on January 1, 2015 and ending on and including January 1, 2024, by 4% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the board of directors.
Shares of common stock reserved for issuance percentage					4.00%
Years of increase in shares of common stock reserved for issuance					10 years
Options granted, Number of Shares					4,016,500
Common stock issued upon exercise of options					326,094	64,938
Unrecognized stock-based compensation cost					$ 8,400	$ 7,800
Unrecognized stock-based compensation cost, weighted-average period recognized					3 years 6 months 10 days	2 years 9 months 14 days
Stock conversion ratio				1 preferred stock = 100 common stock
Stock options granted, exercise price per share					$ 2.91
Common stock issued upon exercise of options aggregate intrinsic value					$ 1,300	$ 300
Conversion of common stock to warrants		10,925,481
Increase In Number Of Shares Reserved For Issuance			4,500,000
Aggregate net proceeds from public offering, net of underwriting commissions					$ 80,691
Stock options outstanding					5,840,538	2,897,294
Research and Development Expense [Member]
Stock-based compensation expense					$ 500	$ 800	$ 1,100
General and Administrative Expense [Member]
Stock-based compensation expense					$ 7,200	$ 3,900	$ 2,700
First year [Member] | Restricted Stock Units (RSUs) [Member]
Vesting Percentage					50.00%
Second year [Member] | Restricted Stock Units (RSUs) [Member]
Vesting Percentage					50.00%
2014 Plan
Maximum number of shares of common stock that may be issued					9,080,445
Shares available to be granted					6,556,534	1,156,378
2014 Plan | Restricted Stock Units (RSUs) [Member]
Award expiration period					10 years
Equity Incentive Plan 2006 [Member]
Stock options outstanding					88,627
Employees And Consultants [Member]
Options granted, Number of Shares					3,830,000
Employees And Consultants [Member] | Restricted Stock Units (RSUs) [Member]
Restricted shares Granted					72,000
Weighted average Fair value Grant					$ 3.47
Employees [Member]
Vesting Percentage					25.00%
Employees [Member] | 2014 Plan
Award expiration period					10 years
Employees [Member] | Minimum [Member]
Stock options granted, exercise price per share					$ 2.71
Employees [Member] | Maximum [Member]
Stock options granted, exercise price per share					$ 5.30
Non-Employee Directors [Member]
Options granted, Number of Shares					110,000
Consultants [Member]
Options granted, Number of Shares					76,500
Vesting Percentage					25.00%
Vesting rights awards					The stock options granted to consultants during the year ended December 31, 2019 have exercise prices per share ranging from $2.82 to $3.76 and have a vesting period of one year in equal monthly installments from the beginning of the vesting period for certain grants and a vesting period of 25% one year after the beginning of the vesting period and thereafter ratably each month over the following thirty-six months for other grants.
Consultants [Member] | Minimum [Member]
Stock options granted, exercise price per share					$ 2.82
Consultants [Member] | Maximum [Member]
Stock options granted, exercise price per share					$ 3.76
Common Stock [Member]
Stock issued for acquisition					4,589,771
Common stock issued upon exercise of options					326,094	64,938	49,280
Sale of shares under public offering	10,263,750				10,263,750
Conversion of common stock to warrants					(10,925,481)
Sale of shares under public offering, price per share	$ 8.40
Underwriting commissions and offering costs	$ 5,500
Aggregate net proceeds from public offering, net of underwriting commissions	$ 80,700
Convertible Preferred Stock, Shares Issued upon Conversion			10,192,700
Aquinox [Member] | Common Stock [Member]
Stock issued for acquisition				4,589,771
Non-voting convertible preferred stock [Member]
Aggregate net proceeds from public offering, net of underwriting commissions
Shares To Be Converted			101,927
Non-voting convertible preferred stock [Member] | Aquinox [Member]
Stock issued for acquisition				101,927
Pre Funded Common Stock Warrants [Member]
Number of common stock in prefunded warrants		10,925,481
Exercise Price Per Share		$ 0.000001
Description of Covenants Under Exercise Of Warrants					The Exchange Warrants may be exercised at any time after the date of issuance, except that the Exchange Warrants cannot be exercised by the stockholders if, after giving effect thereto, the stockholders would beneficially own more than 9.99% of the outstanding common stock, subject to certain exceptions.