Stockholders' Equity - Summary of Stock Option Activity (Detail) - Jun. 30, 2015 - Equity Incentive Plan [Member] - Stock options [Member] - USD ($) $ / shares in Units, $ in Millions	Total
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	581,083
Number of Options, Exercised	(519,560)
Number of Options, Forfeited	(52,345)
Number of Options, Outstanding at June 30, 2015	5,077,135
Number of Options, Vested and exercisable at June 30, 2015	3,399,023
Weighted Average Exercise Price, Outstanding at December 31, 2014	$ 33.52
Weighted Average Exercise Price, Granted	115.77
Weighted Average Exercise Price, Exercised	22.77
Weighted Average Exercise Price, Forfeited	84.17
Outstanding at June 30, 2015	43.51
Vested and exercisable at June 30, 2015	$ 24.62
Weighted Average Remaining Contractual Term (in years), Outstanding at June 30, 2015	6 years 3 months 29 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at June 30, 2015	5 years 2 months 5 days
Aggregate Intrinsic Value, Outstanding at June 30, 2015	$ 361.6
Aggregate Intrinsic Value, Vested and exercisable at June 30, 2015	$ 304.5