Capital Stock and Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Common stock, shares authorized	200,000				200,000				200,000	200,000
Common stock, par value (in dollars per share)	$ 0.01				$ 0.01				$ 0.01	$ 0.01
Preferred stock authorized	20,000								20,000
Perferred stock par value	$ 0.01								$ 0.01
Earnings Per Share, Basic [Abstract]
Net income (loss)	$ 17,839	$ 2,577	$ (6,948)	$ (20,108)	$ 24,511	$ (1,584)	$ 35,289	$ (36,375)	$ (6,639)	$ 21,841	$ (204,900)
Weighted-average shares outstanding									72,907	61,328	61,053
Basic earnings per share (in dollars per share)	$ 0.24	$ 0.03	$ (0.09)	$ (0.3)	$ 0.4	$ (0.03)	$ 0.58	$ (0.59)	$ (0.09)	$ 0.36	$ (3.36)
Earnings Per Share, Diluted [Abstract]
Net income	$ 17,839	$ 2,577	$ (6,948)	$ (20,108)	$ 24,511	$ (1,584)	$ 35,289	$ (36,375)	$ (6,639)	$ 21,841	$ (204,900)
Dilutive effect of stock equivalents									0	962	0
Denominator for diluted earnings (loss) per share									72,907	62,290	61,053
Diluted earnings (loss) per share	$ 0.23	$ 0.03	$ (0.09)	$ (0.3)	$ 0.39	$ (0.03)	$ 0.57	$ (0.59)	$ (0.09)	$ 0.35	$ (3.36)
Anti-dilutive securities excluded from diluted earnings (loss) per share calculation
Anti-dilutive stock equivalents									3,770	1,706	2,276