Stock Option Activity and Weighted Average Exercise Price (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011 Stock Option Plans	Dec. 31, 2010 Stock Option Plans	Dec. 31, 2009 Stock Option Plans	Dec. 31, 2011 Omnibus Incentive Plan	Dec. 31, 2010 Omnibus Incentive Plan	Dec. 31, 2009 Omnibus Incentive Plan	Dec. 31, 2009 Broad Based	Dec. 31, 1999 Broad Based	Dec. 31, 2011 Non Employee Directors, Plan	Dec. 31, 2010 Non Employee Directors, Plan	Dec. 31, 2008 Non Employee Directors, Plan
Outstanding Shares
Beginning Balance	2,473,760	6,439,246	6,811,698	4,308,812	2,837,800	1,551,800	73,600		104,000	176,000	176,000
Granted				1,276,500	1,615,812	1,334,000		1,350,800	8,000
Exercised	(1,373,414)	(3,951,986)	(331,652)	(865,875)	(6,000)		(67,998)		(16,000)	(72,000)
Forfeited	(1,800)	(13,500)	(40,800)	(36,700)	(138,800)	(48,000)	(5,602)		(8,000)
Ending Balance	1,098,546	2,473,760	6,439,246	4,682,737	4,308,812	2,837,800			80,000	104,000	176,000
Vested or expected to vest at end of period	1,098,546			4,480,067					80,000
Options exercisable at end of period	1,098,546			819,725					80,000
Weighted-Average Exercise Price
Beginning Balance	$ 23.36	$ 19.15	$ 18.71	$ 20.54	$ 16.89	$ 20.70	$ 7.89		$ 21.91	$ 23.03	$ 23.03
Granted				$ 50.52	$ 26.81	$ 12.58		$ 7.89
Exercised	$ 21.98	$ 16.50	$ 9.67	$ 16.30	$ 24.25		$ 7.89		$ 18.14	$ 24.65
Forfeited	$ 24.27	$ 21.49	$ 22.39	$ 26.38	$ 18.79	$ 20.09	$ 7.89		$ 13.35
Ending Balance	$ 25.08	$ 23.36	$ 19.15	$ 29.45	$ 20.54	$ 16.89			$ 23.52	$ 21.91	$ 23.03
Vested or expected to vest at end of period	$ 25.08			$ 29.10					$ 23.52
Options exercisable at end of period	$ 25.08			$ 18.26					$ 23.52