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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net income (loss) available to common shareholders	$ (7,348)	$ 35,347	$ 7,621	$ 92,315
Weighted average common shares outstanding - Basic	39,127	39,472	39,325	39,756
Dilutive effect of stock-based awards	0	319	298	286
Weighted average common shares outstanding - Diluted	39,127	39,791	39,623	40,042
Earnings (loss) per common share - Basic	$ (0.19)	$ 0.90	$ 0.19	$ 2.32
Earnings (loss) per common share - Diluted	$ (0.19)	$ 0.89	$ 0.19	$ 2.31