Stock-Based Compensation - Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares, Outstanding, Beginning balance	19,567
Number of Shares, Granted	2,276
Number of Shares, Exercised	(1,464)
Number of Shares, Forfeited	(83)
Number of Shares, Outstanding, Ending balance	20,285	19,567
Number of shares vested and expected to vest	19,937
Number of stock option exercisable	14,302
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 4.47
Weighted Average Exercise Price, Granted	$ 9.09
Weighted Average Exercise Price, Exercised	$ 2.14
Weighted Average Exercise Price, Forfeited	$ 5.69
Weighted Average Exercise Price, Outstanding, Ending balance	$ 5.15	$ 4.47
Weighted average exercise price of shares vested and expected to vest (in dollars per share)	$ 5.11
Weighted average exercise price for exercisable option (in dollars per share)	$ 4.33
Weighted Average Remaining Contractual Term	6 years 6 months 18 days	6 years 2 months 1 day
Weighted Average Remaining Contractual Term, Vested and expected to vest	6 years 6 months 4 days
Weighted Average Remaining Contractual Term, Exercisable	5 years 6 months 11 days
Aggregate Intrinsic Value, Outstanding, Beginning balance	$ 133,599
Aggregate Intrinsic Value, Outstanding, Ending balance	136,489	133,599
Aggregate Intrinsic Value, Vested and expected to vest	134,914
Aggregate Intrinsic Value, Exercisable	$ 107,983