Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Options
Options, Beginning Balance	7,669,553
Options, Granted	2,019,413		3,698,708	1,619,167
Options, Forfeited	(953,472)
Options, Exercised	(2,554,699)	[1]
Options, Ending Balance	6,180,795		7,669,553
Options, Vested and expected to vest	4,738,666
Options, Exercisable	2,506,615
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning Balance	$ 4.08
Weighted Average Exercise Price, Granted	$ 18.35
Weighted Average Exercise Price, Forfeited	$ 6.68
Weighted Average Exercise Price, Exercised	$ 3.73	[1]
Weighted Average Exercise Price, Ending Balance	$ 8.49		$ 4.08
Weighted Average Exercise Price, Vested and expected to vest	$ 7.56
Weighted Average Exercise Price, Exercisable	$ 4.02
Average Intrinsic Value/Weighted Average Exercise Term
Average Intrinsic Value	$ 172,661		$ 56,844
Average Intrinsic Value, Vested and expected to vest	138,012
Average Intrinsic Value, Exercisable	$ 80,962
Weighted Average Exercise Term, Outstanding Balance	7 years 10 months 13 days		8 years 3 months 15 days
Weighted Average Exercise Term, Vested and expected to vest	7 years 8 months 23 days
Weighted Average Exercise Term, Exercisable	7 years 2 months 19 days

[1] Included 138,048 shares of restricted common stock owned by officers of the Company that contained forfeiture provisions.