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, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Options Outstanding, Balance	5,960
Number of Shares, Options Granted	1,202
Number of Shares, Options Exercised	(213)
Number of Shares, Options Forfeited and Cancelled	(2,063)
Number of Shares, Options Outstanding, Balance	4,886	5,960
Number of Shares, Options Exercisable, Balance	3,092
Number of Shares, Options Vested, Balance	3,079
Number of Shares, Options Vested and Expected to Vest, Balance	4,738
Weighted Average Exercise Price Per Share, Options Outstanding, Balance	$ 7.58
Weighted Average Exercise Price Per Share, Options granted	2.66
Weighted Average Exercise Price Per Share, Options exercised	1.64
Weighted Average Exercise Price Per Share, Options forfeited and cancelled	7.48
Weighted Average Exercise Price Per Share, Options Outstanding, Balance	6.67	$ 7.58
Weighted Average Exercise Price Per Share, Options exercisable, Balance	7.89
Weighted Average Exercise Price Per Share, Options vested, Balance	7.87
Weighted Average Exercise Price Per Share, Options vested and expected to vest, Balance	$ 6.75
Weighted Average Remaining Contractual Term, Options Outstanding (in years)	6 years 3 months 4 days	7 years 10 months 6 days
Weighted Average Remaining Contractual Term, Options granted (in years)	7 years 26 days
Weighted Average Remaining Contractual Term, Options exercised (in years)	0 years
Weighted Average Remaining Contractual Term, Options forfeited and cancelled (in years)	0 years
Weighted Average Remaining Contractual Term, Options exercised (in years)	4 years 7 months 24 days
Weighted Average Remaining Contractual Term, Options vested (in years)	4 years 7 months 24 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest (in years)	6 years 2 months 1 day
Aggregate Intrinsic Value, Options Outstanding, Balance	$ 403	$ 957
Aggregate Intrinsic Value, Options exercisable, Balance	226
Aggregate Intrinsic Value, Options vested, Balance	226
Aggregate Intrinsic Value, Options vested and expected to vest, Balance	$ 393