Equity Award Plans - Summary of Activity under the 2006 Plan and 2013 Plan (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Options Outstanding, Balance	5,960	6,376	4,855
Number of Shares, Options Granted	1,202	2,303	3,558
Number of Shares, Options Exercised	(264)	(727)	(791)
Number of Shares, Options Forfeited and Cancelled	(3,149)	(1,992)	(1,246)
Number of Shares, Options Outstanding, Balance	3,749	5,960	6,376	4,855
Number of Shares, Options Exercisable, Balance	2,178
Number of Shares, Options Vested, Balance	2,174
Number of Shares, Options Vested and Expected to Vest, Balance	3,636
Weighted Average Exercise Price Per Share, Options Outstanding, Balance	$ 7.58	$ 7.99	$ 6.56
Weighted Average Exercise Price Per Share, Options granted	2.66	5.85	9.39
Weighted Average Exercise Price Per Share, Options exercised	1.48	1.98	3.12
Weighted Average Exercise Price Per Share, Options forfeited and cancelled	7.79	8.92	9.51
Weighted Average Exercise Price Per Share, Options Outstanding, Balance	6.26	$ 7.58	$ 7.99	$ 6.56
Weighted Average Exercise Price Per Share, Options exercisable, Balance	7.70
Weighted Average Exercise Price Per Share, Options vested, Balance	7.69
Weighted Average Exercise Price Per Share, Options vested and expected to vest, Balance	$ 6.33
Weighted Average Remaining Contractual Term, Options Outstanding (in years)	7 years 5 months 23 days	7 years 10 months 6 days	7 years 9 months 26 days	7 years 10 months 6 days
Weighted Average Remaining Contractual Term, Options granted (in years)	6 years 9 months 26 days	7 years 8 months 12 days	8 years 4 months 6 days
Weighted Average Remaining Contractual Term, Options exercised (in years)	0 years	0 years	0 years
Weighted Average Remaining Contractual Term, Options forfeited and cancelled (in years)	0 years	0 years	0 years
Weighted Average Remaining Contractual Term, Options exercisable (in years)	6 years 5 months 27 days
Weighted Average Remaining Contractual Term, Options vested (in years)	6 years 5 months 27 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest (in years)	7 years 5 months 9 days
Aggregate Intrinsic Value, Options Outstanding, Balance	$ 194	$ 957	$ 9,697	$ 20,593
Aggregate Intrinsic Value, Options exercisable, Balance	110
Aggregate Intrinsic Value, Options vested, Balance	110
Aggregate Intrinsic Value, Options vested and expected to vest, Balance	$ 192