Stockholders' Equity - Summary of Stock Option Activity (Detail) (Stock options [Member], USD $)	6 Months Ended
	Jun. 30, 2013
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding at December 31, 2012	7,038,291
Number of Options, Granted	337,606
Number of Options, Exercised	(308,914)
Number of Options, Forfeited	(18,104)
Number of Options, Outstanding at June 30, 2013	7,048,879
Number of Options, Vested and exercisable at June 30, 2013	4,093,583
Weighted Average Exercise Price, Outstanding at December 31, 2012	$ 18.90
Weighted Average Exercise Price, Granted	$ 49.75
Weighted Average Exercise Price, Exercised	$ 11.82
Weighted Average Exercise Price, Forfeited	$ 35.56
Weighted Average Exercise Price, Outstanding at June 30, 2013	$ 20.65
Weighted Average Exercise Price, Vested and exercisable at June 30, 2013	$ 11.67
Weighted Average Remaining Contractual Term (in years), Outstanding at June 30, 2013	6 years 11 months 12 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at June 30, 2013	5 years 8 months 19 days
Aggregate Intrinsic Value, Outstanding at June 30, 2013	$ 205.8
Aggregate Intrinsic Value, Vested and exercisable at June 30, 2013	$ 153.6