Net Income (Loss) Per Share - EPS Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income (loss) attributable to the Company's common stockholders - Basic									$ (79,079)	$ 43,453	$ (151,392)
Plus (less): effect of participating securities									0	874	0
Net income (loss) attributable to common stockholders									(79,079)	44,327	(151,392)
Less: effect of participating securities									0	(874)	0
Net income (loss) attributable to the Company's common stockholders - Diluted									$ (79,079)	$ 43,453	$ (151,392)
Weighted-average shares outstanding - Basic (in shares)									38,731,015	40,897,549	43,958,803
Adjustment to reflect stock appreciation right conversions (in shares)									0	5,311	0
Weighted-average shares outstanding - Diluted (in shares)									38,731,015	40,902,860	43,958,803
Net income (loss) per share attributable to common stockholders - diluted (in dollars per share)	$ (0.44)	$ (0.29)	$ (0.90)	$ (0.41)	$ 0.51	$ 0.59	$ 0.18	$ (0.14)	$ (2.04)	$ 1.06	$ (3.44)