Net Income (Loss) Per Share - Reconciliation of Basic and Diluted Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net (loss) income	$ (3,438)	$ 28,927	$ (15,674)	$ 54,837
Weighted average shares:
Basic shares (in shares)	36,772	41,091	37,666	41,233
Effect of dilutive securities—options and warrants outstanding (in shares)	0	1,396	0	1,392
Diluted shares (in shares)	36,772	42,487	37,666	42,625
Net income (loss) per share - basic (in dollars per share)	$ (0.09)	$ 0.70	$ (0.42)	$ 1.33
Net income (loss) per share - diluted (in dollars per share)	$ (0.09)	$ 0.68	$ (0.42)	$ 1.29