Equity Award Plans - Summary of Activity under the 2006 Plan and 2013 Plan (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Options Outstanding, Balance	6,376
Number of Shares, Options Granted	2,141
Number of Shares, Options Exercised	(579)
Number of Shares, Options Forfeited and Cancelled	(1,538)
Number of Shares, Options Outstanding, Balance	6,400	6,376
Number of Shares, Options Exercisable, Balance	2,891
Number of Shares, Options Vested, Balance	2,708
Number of Shares, Options Vested and Expected to Vest, Balance	6,068
Weighted Average Exercise Price, Options Outstanding, Balance	$ 7.99
Weighted Average Exercise Price, Options granted	5.99
Weighted Average Exercise Price, Options exercised	1.91
Weighted Average Exercise Price, Options forfeited and cancelled	8.87
Weighted Average Exercise Price, Options Outstanding, Balance	7.66	$ 7.99
Weighted Average Exercise Price, Options exercisable, Balance	7.65
Weighted Average Exercise Price, Options vested, Balance	7.49
Weighted Average Exercise Price, Options vested and expected to vest, Balance	$ 7.67
Weighted Average Remaining Contractual Term, Options Outstanding (in years)	7 years 6 months 7 days	7 years 9 months 26 days
Weighted Average Remaining Contractual Term, Options granted (in years)	7 years 9 months 26 days
Weighted Average Remaining Contractual Term, Options exercised (in years)	0 years
Weighted Average Remaining Contractual Term, Options vested and expected to vest (in years)	0 years
Weighted Average Remaining Contractual Term, Options exercisable (in years)	5 years 6 months 22 days
Weighted Average Remaining Contractual Term, Options vested (in years)	5 years 5 months 16 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest (in years)	7 years 5 months 5 days
Aggregate Intrinsic Value, Options Outstanding, Balance	$ 869	$ 9,697
Aggregate Intrinsic Value, Options exercisable, Balance	869
Aggregate Intrinsic Value, Options vested, Balance	869
Aggregate Intrinsic Value, Options vested and expected, Balance	$ 869