Reconciliation of Earnings Per Share (Details) - Earnings Per Share Reconciliation (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share Reconciliation
Net Income, Basic EPS	$ 2,046	$ 87,599	$ 190,739	$ 245,192
Basic Shares Oustanding (in shares)	72,130	72,068	72,121	72,045
Earnings Per Share, Basic (dollars per share)	$ 0.03	$ 1.22	$ 2.64	$ 3.40
Effect of dilutive securities
Net Income, Diluted EPS	$ 2,046	$ 87,599	$ 190,739	$ 245,192
Diluted Shares Outstanding (in shares)	72,316	72,375	72,301	72,409
Earnings Per Share, Diluted (dollars per share)	$ 0.03	$ 1.21	$ 2.64	$ 3.39
Stock options
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements	183	298	177	355
Non-vested restricted stock
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements	3	9	3	9