Stockholders' Equity - Summary of Stock Option Activity (Detail) - Equity Incentive Plan [Member] - Stock options [Member] $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding at December 31, 2014	10,135,914
Number of Options, Granted	1,631,634
Number of Options, Exercised	(1,278,016)
Number of Options, Forfeited/expired	(230,274)
Number of Options, Outstanding at September 30, 2015	10,259,258
Number of Options, Vested and exercisable at September 30, 2015	6,893,054
Weighted Average Exercise Price, Outstanding at December 31, 2014 | $ / shares	$ 16.76
Weighted Average Exercise Price, Granted | $ / shares	53.86
Weighted Average Exercise Price, Exercised | $ / shares	11.22
Weighted Average Exercise Price, Forfeited/expired | $ / shares	41.34
Outstanding at September 30, 2015 | $ / shares	22.80
Vested and exercisable at September 30, 2015 | $ / shares	$ 13.05
Weighted Average Remaining Contractual Term (in years), Outstanding at September 30, 2015	6 years 2 months 27 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at September 30, 2015	5 years 7 days
Aggregate Intrinsic Value, Outstanding at September 30, 2015 | $	$ 221.5
Aggregate Intrinsic Value, Vested and exercisable at September 30, 2015 | $	$ 203.1