Stockholders' equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 27, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares authorized		55,000,000		55,000,000
Common stock, shares authorized		50,000,000		50,000,000		50,000,000
Common stock, par value		$ 0.000001		$ 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		10,727,221		10,727,221		10,695,108
Common stock, shares outstanding		10,727,221		10,727,221		10,695,108
Preferred stock, shares issued		0		0		0
Preferred stock, shares outstanding		0	0	0	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				287,750
Stock options granted, exercise price per share				$ 11.42
Stock options, vesting period				5 years 10 months 28 days
Common stock issued upon exercise of options				32,113
Stock-based compensation expense		$ 455	$ 215	$ 721	$ 352
Unrecognized stock-based compensation cost		$ 4,166	$ 3,044	$ 4,166	$ 3,044
Unrecognized stock-based compensation cost, weighted-average period recognized				2 years 11 months 12 days	2 years 8 months 9 days
Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted				257,750
Employees [Member] | Vesting of stock options granted to employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, vesting percentage				25.00%
Employees [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted, exercise price per share				$ 7.45
Employees [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted, exercise price per share				$ 12.03
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted				30,000
Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted, exercise price per share				$ 12.03
Non-employee Directors [Member] | Condition (i) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, vesting period				1 year
Non-employee Directors [Member] | Condition (ii) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, vesting period				3 years
Equity Incentive Plan 2006 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted	0
Equity Incentive Plan 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares of common stock that may be issued		1,851,220		1,851,220
Stock options, expiration period				10 years