Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income (loss) available to common shareholders	$ (9,885)	$ 12,640	$ 20,121	$ 3,692
Weighted average common shares outstanding - Basic	38,248	38,114	38,181	38,329
Dilutive effect of stock-based awards	0	244	334	262
Weighted average common shares outstanding - Diluted	38,248	38,358	38,515	38,591
Earnings (loss) per common share - Basic	$ (0.26)	$ 0.33	$ 0.53	$ 0.10
Earnings (loss) per common share - Diluted	$ (0.26)	$ 0.33	$ 0.52	$ 0.10