Earnings Per Share and Capital Structure Computation of Basic and Diluted Earnings per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income (loss) available to common shareholders	$ 108,275	$ (510,157)	$ 104,770
Weighted average common shares outstanding - Basic	39,625,000	40,612,000	40,337,000
Dilutive effect of convertible notes	0	0	103,000
Dilutive effect of stock-based awards	309,000	0	507,000
Weighted average common shares outstanding - Diluted	39,934,000	40,612,000	40,947,000
Earnings (loss) per common share - Basic	$ 2.73	$ (12.56)	$ 2.60
Earnings (loss) per common share - Diluted	$ 2.71	$ (12.56)	$ 2.56