Earnings Per Share and Capital Structure Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net income (loss) available to common shareholders	$ (14,198)	$ 19,259	$ (9,288)	$ 19,005
Weighted average common shares outstanding - Basic	38,434	39,356	38,438	39,296
Dilutive effect of stock-based awards	0	188	0	232
Weighted average common shares outstanding - Diluted	38,434	39,544	38,438	39,528
Earnings (loss) per common share - Basic	$ (0.37)	$ 0.49	$ (0.24)	$ 0.48
Earnings (loss) per common share - Diluted	$ (0.37)	$ 0.49	$ (0.24)	$ 0.48