Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Components of the provision for income taxes
Federal	$ 0	$ 4,607	$ 0	$ (2,832)
State	40	2,439	(585)	(1,403)
Deferred portion of income tax (expense) benefit	861	64,015	(97,505)	30,790
Income tax (expense) benefit	$ 901	$ 71,061	$ (98,090)	$ 26,555
Effective tax rate	(5.50%)	37.20%	22.70%	36.90%
Tax Year 2017 [Member]
Federal enacted statutory income tax rate, percent			35.00%
Future tax years [Member]
Federal enacted statutory income tax rate, percent			21.00%