Stock Based Awards - Summary of Stock Options Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares Available for Grant
Shares Available for Grant, Beginning balance	1,044,113	1,350,543	991,401
Shares Available for Grant, Additional shares authorized	1,567,975	1,323,911	1,091,045
Shares Available for Grant, Options granted	(1,364,700)	(1,399,522)	(664,100)
Shares Available for Grant, Restricted stock units granted	(2,568,333)	(332,964)	(123,450)
Shares Available for Grant, Options cancelled	1,320,949	102,145	55,647
Shares Available for Grant, Ending balance	4	1,044,113	1,350,543
Number of shares
Number of Shares, Beginning balance	4,452,700	3,240,969	2,723,367
Number of Shares, Options granted	1,364,700	1,399,522	664,100
Number of Shares, Options exercised	(850,995)	(85,646)	(90,851)
Number of Shares, Options cancelled	(1,320,949)	(102,145)	(55,647)
Number of Shares, Ending balance	3,645,456	4,452,700	3,240,969
Number of Shares, Vested and expected to vest	3,569,972
Number of Shares, Exercisable	2,345,851
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning balance	$ 11.16	$ 11.51	$ 10.33
Weighted Average Exercise Price, Options granted	15.92	10.04	15.34
Weighted Average Exercise Price, Options exercised	2.94	1.64	1.34
Weighted Average Exercise Price, Options cancelled	14.65	14.90	15.68
Weighted Average Exercise Price, Ending balance	13.60	$ 11.16	$ 11.51
Weighted Average Exercise Price, Vested and expected to vest	13.56
Weighted Average Exercise Price, Exercisable	$ 12.85
Weighted Average Remaining Contractual Life (in years)
Weighted Average Remaining Contractual Life, Options outstanding	6 years 3 months 18 days
Weighted Average Remaining Contractual Life, Vested and expected to vest	6 years 6 months
Weighted Average Remaining Contractual Life, Exercisable	5 years
Aggregate Intrinsic Value, Options outstanding	$ 38
Aggregate Intrinsic Value, Vested and expected to vest	38
Aggregate Intrinsic Value, Exercisable	$ 31