Income (Loss) Per Common Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income (Loss) Per Share
Net income (loss)	$ (144,674)	$ (8,953)	$ (237,634)	$ (15,827)	$ (8,479)	$ (23,740)	$ (20,817)	$ 1,640	$ (407,088)	$ (51,396)	$ (122,027)
Net income (loss) per common share:
Basic (in dollars per share)	$ (3.11)	$ (0.19)	$ (5.02)	$ (0.34)	$ (0.18)	$ (0.51)	$ (0.49)	$ 0.04	$ (8.63)	$ (1.16)	$ (3.10)
Diluted (in dollars per share)	$ (3.11)	$ (0.19)	$ (5.02)	$ (0.34)	$ (0.18)	$ (0.51)	$ (0.49)	$ 0.04	$ (8.63)	$ (1.16)	$ (3.10)
Weighted average shares reconciliation
Basic weighted average shares outstanding									47,151	44,174	39,340
Diluted weighted average shares outstanding									47,151	44,174	39,340