Reconciliation of Earnings Per Share (Details) - Earnings Per Share Reconciliation (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share Reconciliation
Net Income, Basic EPS	$ 63,325	$ 55,543	$ 157,593	$ 172,253
Basic Shares Oustanding (in shares)	72,065	71,844	72,033	71,830
Earnings Per Share, Basic (dollars per share)	$ 0.88	$ 0.77	$ 2.19	$ 2.40
Effect of dilutive securities
Net Income, Diluted EPS	$ 63,325	$ 55,543	$ 157,593	$ 172,253
Diluted Shares Outstanding (in shares)	72,420	72,089	72,364	72,069
Earnings Per Share, Diluted (dollars per share)	$ 0.87	$ 0.77	$ 2.18	$ 2.39
Stock options
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements	347	228	324	223
Non-vested restricted stock
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements	8	17	7	16