Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Options, Outstanding, Beginning balance	19,211
Number of Options, Granted	4,189
Number of Options, Exercised	(1,196)
Number of Options, Forfeited	(1,204)
Number of Options, Outstanding, Ending balance	21,000	19,211
Number of Options, Vested and expected to vest	20,658
Number of Options, Exercisable	15,691
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 5.72
Weighted-Average Exercise Price, Granted	5.57
Weighted-Average Exercise Price, Exercised	3.37
Weighted-Average Exercise Price, Forfeited	6.89
Weighted-Average Exercise Price, Outstanding, Ending balance	5.76	$ 5.72
Weighted-Average Exercise Price, Vested and expected to vest	5.75
Weighted-Average Exercise Price, Exercisable	$ 5.40
Weighted-Average Remaining Contractual Term	6 years 4 days	6 years 2 months 27 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	5 years 11 months 16 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 1 month 21 days
Aggregate Intrinsic Value, Outstanding	$ 26,505	$ 47,963
Aggregate Intrinsic Value, Vested and expected to vest	26,271
Aggregate Intrinsic Value, Exercisable	$ 23,323