Reconciliation of Earnings Per Share (Details) - Earnings Per Share Reconciliation (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share Reconciliation
Net Income, Basic EPS	$ 87,599	$ 38,304	$ 245,192	$ 210,557
Basic Shares Oustanding (in shares)	72,068	71,854	72,045	71,838
Earnings Per Share, Basic (dollars per share)	$ 1.22	$ 0.53	$ 3.40	$ 2.93
Effect of dilutive securities
Net Income, Diluted EPS	$ 87,599	$ 38,304	$ 245,192	$ 210,557
Diluted Shares Outstanding (in shares)	72,375	72,070	72,409	72,061
Earnings Per Share, Diluted (dollars per share)	$ 1.21	$ 0.53	$ 3.39	$ 2.92
Stock options
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements	298	199	355	206
Non-vested restricted stock
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements	9	17	9	17