Quarterly Results of Operations (unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 141,505	$ 149,332	$ 154,782	$ 144,478	$ 126,287	$ 117,281	$ 107,130	$ 95,757	$ 590,097	$ 446,455	$ 277,076
Income (loss) from operations	(3,752)	4,338	(8,803)	(842)	(8,736)	(10,892)	(12,729)	(18,873)	(9,059)	(51,230)	(113,448)
Income tax benefit (expense)	(611)	(258)	249	(1,288)	5,403	(17)	(1,135)	(48)	(1,908)	4,203	10,732
Net loss	$ (14,487)	$ (5,233)	$ (18,152)	$ (11,139)	$ (12,558)	$ (17,227)	$ (20,209)	$ (25,124)	$ (49,011)	$ (75,118)	$ (128,391)
Loss per share:
Loss per common share - Basic	$ (0.19)	$ (0.07)	$ (0.23)	$ (0.14)	$ (0.16)	$ (0.22)	$ (0.26)	$ (0.33)	$ (0.63)	$ (0.97)	$ (1.96)
Loss per common share - Diluted	$ (0.19)	$ (0.07)	$ (0.23)	$ (0.14)	$ (0.16)	$ (0.22)	$ (0.26)	$ (0.33)	$ (0.63)	$ (0.97)	$ (1.96)