Net Loss Per Share - 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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic and diluted:
Net loss	$ (492)	$ (44,799)	$ (17,479)	$ (99,383)
Basic:
Weighted-average common shares outstanding, basic (in shares)	49,386	49,230	49,328	48,371
Dilutive effect of stock options	0	0	0	0
Diluted:
Weighted-average common shares outstanding, diluted (in shares)	49,386	49,230	49,328	48,371
Net loss per share:
Basic (in dollars per share)	$ (0.01)	$ (0.91)	$ (0.35)	$ (2.05)
Diluted (in dollars per share)	$ (0.01)	$ (0.91)	$ (0.35)	$ (2.05)