Stockholders' Equity (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based compensation
Tax benefit from exercise of stock options and vesting of stock awards	$ 2,038,000	$ 1,121,000	$ 2,917,000
Net adjustment to additional paid in capital related to excess tax benefits and deficiencies associated with share-based compensation awards	2,000,000	(1,400,000)	2,900,000
Gross tax deficiencies related to share-based compensation awards		1,100,000
Gross tax benefits related to share-based compensation awards		2,500,000
Stock options
Share-based compensation
Vesting period (in years)	3 years
Expiration period (in years)	P10Y
Stock option activity
Outstanding, beginning of period (in shares)	3,775,586	5,185,091	4,668,490
Granted (in shares)	1,217,958	951,072	1,326,694
Forfeited (in shares)	(86,986)	(332,105)	(732,846)
Exercised (in shares)	(1,065,325)	(2,028,472)	(77,247)
Outstanding, end of period (in shares)	3,841,233	3,775,586	5,185,091
Vested and expected to vest end of period (in shares)	3,763,158
Exercisable, end of period (in shares)	1,720,871
Weighted average exercise price of stock options
Outstanding, beginning of period (in dollars per share)	$ 39.27	$ 38.19	$ 39.82
Granted (in dollars per share)	$ 49.30	$ 42.70	$ 33.00
Forfeited (in dollars per share)	$ 42.13	$ 40.66	$ 39.68
Exercised (in dollars per share)	$ 38.34	$ 37.89	$ 33.38
Outstanding, end of period (in dollars per share)	$ 42.65	$ 39.27	$ 38.19
Vested and expected to vest end of period (in dollars per share)	$ 42.55
Exercisable, end of period (in dollars per share)	$ 40.02
Weighted average remaining contractual term
Outstanding, end of period (in years)	7.47
Vested and expected to vest end of period (in years)	7.44
Exercisable, end of period (in years)	6.03
Aggregate intrinsic value
Outstanding, end of the period	26,446,000
Vested and expected to vest end of period	26,251,000
Exercisable, end of period	16,268,000
Closing stock price (in dollars per share)	$ 49.47
Total pre-tax intrinsic value of options exercised	13,100,000	18,200,000	400,000
Grants in period, weighted average grant date fair value (in dollars per share)	$ 12.72	$ 11.74	$ 8.69
Estimates used for determining weighted average grant date fair value
Risk-free interest rate (as a percent)	1.63%	1.74%	1.67%
Expected life (in years)	4	4	4
Expected volatility (as a percent)	29.88%	31.70%	30.20%
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%
Unrecognized compensation expense	16,900,000
Unrecognized compensation expense, period of recognition (in years)	1.89
Aggregate fair value of options vested	$ 10,300,000
Nonvested restricted stock units
Share-based compensation
Vesting period (in years)	3 years
2011 Management Incentive Plan
Share-based compensation
Maximum number of shares available	5,000,000
Multiplier for delivery of shares under full-value awards	2.29
Number of shares available for grant	4,886,385