Share-Based Employee Compensation - Additional Information (Detail) (USD $)	12 Months Ended														1 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2011 Year	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Omnibus Incentive Plan	Dec. 31, 2010 Omnibus Incentive Plan	Dec. 31, 2009 Omnibus Incentive Plan	Dec. 31, 2011 Omnibus Incentive Plan Minimum	Dec. 31, 2011 Omnibus Incentive Plan Maximum	Dec. 31, 2011 Omnibus Incentive Plan Deferred Stock Units Non-employee directors	Dec. 31, 2010 Omnibus Incentive Plan Deferred Stock Units Non-employee directors	Dec. 31, 2009 Omnibus Incentive Plan Deferred Stock Units Non-employee directors	Dec. 31, 2011 Omnibus Incentive Plan Deferred Stock Units Non-employee directors Since 2007	Dec. 31, 2011 Stock Option Plans	Dec. 31, 2011 Stock Option Plans Minimum	Mar. 31, 2002 Broad Based	Dec. 31, 1999 Broad Based	Dec. 31, 2011 Broad Based Maximum	Dec. 31, 2011 Restricted Stock	Dec. 31, 2010 Restricted Stock	Dec. 31, 2009 Restricted Stock	Dec. 31, 2011 Non Employee Directors, Plan	Dec. 31, 2011 Non Employee Directors, Plan Maximum	Dec. 31, 2011 Directors Plan	Dec. 31, 2010 Directors Plan	Dec. 31, 2011 Long Term Incentive Plans	Dec. 31, 2010 Long Term Incentive Plans	Dec. 31, 2011 Stock Options	Dec. 31, 2011 Employee Stock Ownership Plan (ESOP), Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares of common stock available for issuance				13,500,000									16,400,000				1,400,000	4,700,000				400,000						7,200,000
Restricted shares awarded, minimum restriction period				2 years														2 years
Stock option awards granted, vesting period							2 years	4 years					3 years
Restricted shares awarded, maximum restriction period				4 years														4 years
Common stock shares granted				1,276,500	1,615,812	1,334,000			16,000	20,000	32,000	106,000				1,350,800					8,000
Exercise price of stock option granted				$ 50.52	$ 26.81	$ 12.58										$ 7.89
Options granted, exercise period																					no later than 10 years from the date of grant
Aggregate option vested															1,036,800
Stock option awards granted, expiration period							10 years							10 years
Options granted, maximum exercise period																						10 years
Maximum shares of common stock authorized																							500,000
Shares of common stock earned																							248,900
Additional shares issued to retired directors																							200,400
Liabilities under share plan																							$ 13,933,000	$ 8,992,000	$ 93,765,000	$ 49,745,000
Unrecognized compensation cost related to unvested share-based awards	35,567,000																	6,570,000									28,997,000
Weighted average period of recognition of unvested share-based awards (in years)	1.80
Weighted average remaining contractual life of option outstanding	7.18
Estimated weighted average fair value of option	$ 18.44	$ 9.30	$ 2.95
Total intrinsic value of options exercised	77,736,000
Total intrinsic value of options outstanding and exercisable	67,466,000	40,795,000	25,962,000
Expenses related ESOP	7,011,000	8,123,000	0
Shares vested under ESOP	4,659,000
Matching contributions to 401(k) retirement savings plan	8,456,000	7,073,000	6,827,000
Maximum percentage of compensation, on a pre-tax basis, employees may choose to contribute	50.00%
Matching percentage of employer to employee contributions	100.00%
Maximum percentage of employee contributions that the company matches	5.00%
Weighted average fair values at the grant dates of grants awarded																		$ 42.54	$ 28.95	$ 17.84
Total intrinsic value of restricted stock expected to vest																		$ 23,749,000