Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income (loss)	$ (8,495)	$ (8,040)	$ 34,544	$ 30,620
Average common shares outstanding - basic (in shares)	28,678	27,554	28,653	27,504
Additional shares for stock-based compensation plans (in shares)	0	0	81	125
Average common shares outstanding - diluted (in shares)	28,678	27,554	28,734	27,629
Earnings per share of common stock - basic (in dollars per share)	$ (0.30)	$ (0.29)	$ 1.21	$ 1.11
Earnings per share of common stock - diluted (in dollars per share)	$ (0.30)	$ (0.29)	$ 1.20	$ 1.11
Antidilutive shares (in shares)	96	159	15	5