Income (Loss) Per Common Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Income (Loss) Per Common Share
Net income (loss)	$ (15,565)	$ (18,530)	$ (237,634)	$ (15,827)	$ (34,095)	$ (253,461)
Net income (loss) per common share:
Basic (in dollars per share)	$ (0.33)		$ (5.02)		$ (0.72)	$ (5.35)
Diluted (in dollars per share)	$ (0.33)		$ (5.02)		$ (0.72)	$ (5.35)
Weighted average shares reconciliation
Basic weighted average shares outstanding	47,112		47,311		47,145	47,332
Diluted weighted average shares outstanding	47,112		47,311		47,145	47,332