Stock-Based Compensation Expense - Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding, Shares	6,138
Granted	2,115
Exercised	(1,232)
Forfeited or expired	(209)
Outstanding, Shares	6,812
Exercisable, Shares	2,208
Options vested or expected to vest	6,098	[1]
Outstanding, Weighted-Average Exercise Price	$ 15.65
Granted, Weighted-Average Exercise Price	$ 39.49
Exercised, Weighted-Average Exercise Price	$ 13.74
Forfeited or expired, Weighted-Average Exercise Price	$ 20.12
Outstanding, Weighted-Average Exercise Price	$ 23.26
Exercisable, Weighted-Average Exercise Price	$ 13.38
Options vested or expected to vest, Weighted-Average Exercise Price	$ 22.04	[1]
Outstanding, Weighted-Average Remaining Contractual Term (in years)	7 years 3 months 12 days
Exercisable, Weighted-Average Remaining Contractual Term (in years)	5 years 2 months 24 days
Options vested or expected to vest, Weighted-Average Remaining Contractual Term (in years)	7 years 1 month 0 days	[1]
Outstanding, Aggregate Intrinsic Value	$ 123,252
Exercisable, Aggregate Intrinsic Value	61,711
Options vested or expected to vest, Aggregate Intrinsic Value	$ 117,733	[1]

[1] (1) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. Options expected to vest are calculated by applying an estimated forfeiture rate to the unvested options.