Equity Incentive Plans - Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award Options Activity [Abstract]
Number of Shares Outstanding, Beginning Balance	7,717	8,207	7,205
Number of Shares, Granted	350	2,815	2,592
Number of Shares, Exercised	(1,042)	(1,683)	(50)
Number of Shares, Forfeited or cancelled	(1,470)	(1,622)	(1,540)
Number of Shares Outstanding, Ending Balance	5,555	7,717	8,207
Number of Shares, Vested and Exercisable	2,594
Number of Shares, Vested and Expected to vest	3,546
Weighted-Average Exercise Price, Beginning Balance	$ 4.05	$ 4.55	$ 6.68
Weighted-Average Exercise Price, Granted	$ 4.4	$ 2.18	$ 1.64
Weighted-Average Exercise Price, Exercised	$ 1.77	$ 1.67	$ 0.46
Weighted-Average Exercise Price, Forfeited or cancelled	$ 8.53	$ 5.70	$ 9.72
Weighted-Average Exercise Price, Ending Balance	$ 3.33	$ 4.05	$ 4.55
Weighted-Average Exercise Price, Vested and Exercisable	$ 4.69
Weighted-Average Exercise Price Vested and Expected to Vest	$ 2.24
Weighted-Average Remaining Contractual Life (Years)	6 years 1 month 13 days
Weighted-Average Remaining Contractual Life (Years), Vested and Exercisable	3 years 10 months 28 days
Weighted-Average Remaining Contractual Life (Years), Vested and Expected to Vest	8 years 4 days
Aggregate Intrinsic Value, Exercised	$ 5,036	$ 4,965	$ 45
Aggregate Intrinsic Value, Outstanding	19,015	22,023
Aggregate Intrinsic Value, Vested and Exercisable	6,157
Aggregate Intrinsic Value, Vested and Expected to Vest	$ 15,046