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, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares, Outstanding, Beginning balance	19,556
Number of Shares, Granted	3,314
Number of Shares, Exercised	(3,080)
Number of Shares, Forfeited	(354)
Number of Shares, Outstanding, Ending balance	19,436	19,556
Number of shares vested and expected to vest	19,113
Number of stock option exercisable	14,620
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 4.47
Weighted Average Exercise Price, Granted	9.68
Weighted Average Exercise Price, Exercised	2.71
Weighted Average Exercise Price, Forfeited	7.26
Weighted Average Exercise Price, Outstanding, Ending balance	5.59	$ 4.47
Weighted average exercise price of shares vested and expected to vest (in dollars per share)	5.54
Weighted average exercise price for exercisable option (in dollars per share)	$ 4.85
Weighted Average Remaining Contractual Term	6 years 4 months 28 days	6 years 2 months 1 day
Weighted Average Remaining Contractual Term, Vested and expected to vest	6 years 4 months 13 days
Weighted Average Remaining Contractual Term, Exercisable	5 years 7 months 2 days
Aggregate Intrinsic Value, Outstanding, Beginning balance	$ 133,599
Aggregate Intrinsic Value, Outstanding, Ending balance	60,544	$ 133,599
Aggregate Intrinsic Value, Vested and expected to vest	60,261
Aggregate Intrinsic Value, Exercisable	$ 54,333