Stock-Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Additional shares of Class A common stock authorized for awards granted under the Omnibus Plan	2,500,000
Total shares of Class A common stock authorized for awards granted under the Omnibus Plan	6,187,500
Shares of Class A common stock available for future issuance under the Omnibus Plan Reserved for Future Issuance	3,230,954
Options Outstanding [Abstract]
Outstanding at beginning of year	1,801,467	2,296,000
Granted	226,304
Exercised	(548,359)
Expired	(6,350)
Forfeited	(13,373)
Outstanding at end of year	1,459,689	1,801,467	2,296,000
Vested or expected to vest at end of year	1,453,897
Exercisable at end of year	934,204
Weighted Average Exercise Price [Abstract]
Beginning of year	$ 31.77
Granted	$ 55.78
Exercised	$ 30.56
Expired	$ 29.41
Forfeited	$ 35.03
End of year	$ 35.93	$ 31.77
Vested or expected to vest at end of year	$ 35.86
Exercisable at end of year	$ 32.67
Weighted Average Remaining Contractual Term (in Years) [Abstract]
Outstanding at end of year	2.4
Vested or expected to vest at end of year	2.4
Exercisable at end of year	1.7
Aggregate Intrinsic Value [Abstract]
Outstanding at end of year	$ 36,002,000
Vested or expected to vest at end of year	35,960,000
Exercisable at end of year	26,077,000
Weighted average grant date fair value of options	$ 15.76	$ 10.76	$ 8.63
Total intrinsic value of options exercised during the year	$ 14,900,000	$ 10,800,000	$ 3,700,000