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								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income (loss) available to common shareholders	$ (154,430)	$ (7,348)	$ 12,399	$ 2,570	$ 15,960	$ 35,347	$ 31,615	$ 25,353	$ (146,809)	$ 108,275	$ (510,157)
Weighted average common shares outstanding - Basic									39,281	39,625	40,612
Dilutive effect of stock-based awards									0	309	0
Weighted average common shares outstanding - Diluted									39,281	39,934	40,612
Earnings (loss) per common share - Basic	$ (3.93)	$ (0.19)	$ 0.31	$ 0.07	$ 0.40	$ 0.90	$ 0.79	$ 0.64	$ (3.74)	$ 2.73	$ (12.56)
Earnings (loss) per common share - Diluted	$ (3.93)	$ (0.19)	$ 0.31	$ 0.06	$ 0.40	$ 0.89	$ 0.79	$ 0.63	$ (3.74)	$ 2.71	$ (12.56)