Share Based Compensation - Summary of Changes in Number of Shares of Common Stock Under Option (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding, Beginning Balance	6,565,000
Shares, Granted	60,000	0
Shares, Exercised	(298,000)
Shares, Outstanding, Ending Balance	6,327,000
Shares, Expected to vest	6,327,000
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 22.17
Weighted Average Exercise Price, Granted	$ 58.02
Weighted Average Exercise Price, Exercised	$ 18.20
Weighted Average Exercise Price, Outstanding, Ending balance	$ 22.70
Weighted Average Exercise Price, Expected to vest	$ 22.70
Options Exercisable at End of Period, Outstanding, Beginning Balance	2,666,000
Options Exercisable at End of Period, Outstanding, Ending Balance	2,476,000
Weighted Average Exercise Price of Exercisable Options, Outstanding, Beginning Balance	$ 14.71
Weighted Average Exercise Price of Exercisable Options, Outstanding, Ending Balance	$ 14.42
Weighted Average Fair Value of Options Granted During the Period, Granted	$ 16.29
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 206,636
Aggregate Intrinsic Value, Exercised	17,404
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 341,471