Stockholders' equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Jan. 27, 2014	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
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		17,211,986		17,211,986
Common stock, shares outstanding		17,211,986		17,211,986
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		396,960
Stock options granted, exercise price per share		$ 8.29
Common stock issued upon exercise of options		0
Stock-based compensation expense		$ 433	$ 266
Unrecognized stock-based compensation cost		$ 4,839	$ 4,504
Unrecognized stock-based compensation cost, weighted-average period recognized		3 years 2 months 16 days	3 years 1 month 2 days
Employees [Member]
Equity Transactions And Share Based Compensation [Line Items]
Stock options granted		396,960
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] | Minimum [Member]
Equity Transactions And Share Based Compensation [Line Items]
Stock options granted, exercise price per share		$ 8.08
Employees [Member] | Maximum [Member]
Equity Transactions And Share Based Compensation [Line Items]
Stock options granted, exercise price per share		$ 10.09
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 2006 [Member]
Equity Transactions And Share Based Compensation [Line Items]
Stock options granted	0
Equity Incentive Plan 2014 [Member]
Equity Transactions And Share Based Compensation [Line Items]
Maximum number of shares of common stock that may be issued		1,960,235
Stock options, expiration period		10 years