Stockholders' Equity - Summary of Stock Option Activity (Detail) (Stock options [Member], USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding at December 31, 2014	5,067,957
Number of Options, Granted	507,916
Number of Options, Exercised	(374,281)
Number of Options, Forfeited	(18,502)
Number of Options, Outstanding at March 31, 2015	5,183,090
Number of Options, Vested and exercisable at March 31, 2015	3,323,776
Weighted Average Exercise Price, Outstanding at December 31, 2014	$ 33.52
Weighted Average Exercise Price, Granted	$ 114.56
Weighted Average Exercise Price, Exercised	$ 23.07
Weighted Average Exercise Price, Forfeited	$ 78.60
Weighted Average Exercise Price, Outstanding at March 31, 2015	$ 42.06
Weighted Average Exercise Price, Vested and exercisable at March 31, 2015	$ 22.56
Weighted Average Remaining Contractual Term (in years), Outstanding at March 31, 2015	6 years 6 months 22 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at March 31, 2015	5 years 3 months 29 days
Aggregate Intrinsic Value, Outstanding at March 31, 2015	$ 451.0
Aggregate Intrinsic Value, Vested and exercisable at March 31, 2015	$ 354.0