Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Components of the provision for income taxes
Federal	$ 0	$ (7,439)
State	(625)	(3,842)
Deferred portion of income tax expense	(98,366)	(33,225)
Income tax expense	$ (98,991)	$ (44,506)
Effective tax rate	23.80%	37.40%
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%