Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Number of Shares
Outstanding, beginning	12,649,102	11,329,218	10,399,265
Granted	2,219,587	2,576,292	2,041,300
Exercised	(456,082)	(485,260)	(825,884)
Forfeited	(296,162)	(557,109)	(202,882)
Expired	(279,594)	(214,039)	(82,581)
Outstanding, ending	13,836,851	12,649,102	11,329,218
Vested (exercisable) — December 31, 2015	10,235,721
Unvested (unexercisable) — December 31, 2015	3,601,130
Weighted- Average Exercise Price/Share
Outstanding, beginning	$ 7.12	$ 7.10	$ 6.57
Granted	6.04	7.60	8.92
Exercised	4.45	4.77	4.40
Forfeited	8.06	9.65	8.22
Expired	9.05	10.70	8.91
Outstanding, ending	6.97	$ 7.12	$ 7.10
Vested (exercisable) — December 31, 2015	6.94
Unvested (unexercisable) — December 31, 2015	$ 7.06
Weighted-Average Remaining Contractual Term (Years), Outstanding	6 years 4 months 4 days
Weighted-Average Remaining Contractual Term (Years), Vested (exercisable)	5 years 4 months 25 days
Weighted-Average Remaining Contractual Term (Years), Unvested (unexercisable)	9 years 1 day
Stock options exercised, Intrinsic value	$ 977	$ 1,629	$ 3,435
Outstanding, Aggregate Intrinsic Value	7,516
Aggregate Intrinsic Value, Vested (exercisable)	7,159
Aggregate Intrinsic Value, Unvested (unexercisable)	$ 357