Stockholders' equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Equity Transactions And Share Based Compensation [Line Items]
Total number of shares authorized	55,000,000
Common stock, shares authorized	50,000,000		50,000,000
Common stock, par value	$ 0.000001		$ 0.000001
Preferred stock, shares authorized	5,000,000
Preferred stock, par value	$ 0.000001
Common stock, shares issued	23,423,150		23,423,150
Common stock, shares outstanding	23,423,150		23,423,150
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 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
Stock options granted	696,100
Stock options granted, exercise price per share	$ 17.35
Common stock issued upon exercise of options	0
Stock-based compensation expense	$ 631	$ 433
Unrecognized stock-based compensation cost	$ 12,807	$ 4,839
Unrecognized stock-based compensation cost, weighted-average period recognized	3 years 4 months 2 days	3 years 2 months 16 days
Employees [Member]
Equity Transactions And Share Based Compensation [Line Items]
Stock options granted	696,100
Stock options granted, exercise price per share	$ 17.35
Employees [Member] | One Year after the Beginning of the Vesting Period [Member]
Equity Transactions And Share Based Compensation [Line Items]
Stock options, vesting percentage	25.00%
Employees [Member] | Condition (i) [Member]
Equity Transactions And Share Based Compensation [Line Items]
Stock options, vesting period	1 year
Employees [Member] | Condition (ii) [Member]
Equity Transactions And Share Based Compensation [Line Items]
Stock options, vesting period	3 years
Equity Incentive Plan 2014 [Member]
Equity Transactions And Share Based Compensation [Line Items]
Maximum number of shares of common stock that may be issued	2,890,063
Stock options, expiration period	10 years