Stockholders' Equity - Summary of Stock Option Activity (Detail) (Stock Options [Member], USD $)	3 Months Ended
	Mar. 31, 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	37,200
Number of Options, Exercised	(177,815)
Number of Options, Forfeited
Number of Options, Outstanding at March 31, 2013	6,897,676
Number of Options, Vested and exercisable at March 31, 2013	3,908,361
Weighted Average Exercise Price, Outstanding at December 31, 2012	$ 18.90
Weighted Average Exercise Price, Granted	$ 52.46
Weighted Average Exercise Price, Exercised	$ 10.25
Weighted Average Exercise Price, Forfeited
Weighted Average Exercise Price, Outstanding at March 31, 2013	$ 19.31
Weighted Average Exercise Price, Vested and exercisable at March 31, 2013	$ 11.12
Weighted Average Remaining Contractual Term (in years), Outstanding at March 31, 2013	7 years 1 month 2 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at March 31, 2013	5 years 10 months 10 days
Aggregate Intrinsic Value, Outstanding at March 31, 2013	$ 195.7
Aggregate Intrinsic Value, Vested and exercisable at March 31, 2013	$ 139.3