Income (Loss) Per Common Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Income (Loss) Per Common Share
Net income (loss)	$ (11,767)	$ (15,565)	$ (18,530)	$ (8,953)	$ (237,634)	$ (15,827)	$ (45,862)	$ (262,414)
Net income (loss) per common share:
Basic (in dollars per share)	$ (0.25)			$ (0.19)			$ (0.97)	$ (5.55)
Diluted (in dollars per share)	$ (0.25)			$ (0.19)			$ (0.97)	$ (5.55)
Weighted average shares reconciliation
Basic weighted average shares outstanding	47,489			46,982			47,361	47,283
Diluted weighted average shares outstanding	47,489			46,982			47,361	47,283