Earnings Per Share and Capital Structure Computation of Basic and Diluted Earnings per Share (Details) (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
Net income (loss) available to common shareholders	$ 35,347	$ (517,082)	$ 92,315	$ (455,526)
Weighted average common shares outstanding-Basic	39,472	40,725	39,756	40,648
Dilutive effect of stock-based awards	319	0	286	0
Weighted average common shares outstanding-Diluted	39,791	40,725	40,042	40,648
Earnings per common share-Basic	$ 0.90	$ (12.70)	$ 2.32	$ (11.21)
Earnings per common share-Diluted	$ 0.89	$ (12.70)	$ 2.31	$ (11.21)