Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Proceeds from Income Tax Refunds			$ 5,900
Components of the provision for income taxes
Federal	$ 0	$ 2,832	0	$ 0
State	(85)	(230)	(670)	(1,633)
Deferred portion of income tax (expense) benefit	36,833	36,668	(60,672)	67,458
Income tax (expense) benefit	$ 36,748	$ 39,270	$ (61,342)	$ 65,825
Effective tax rate	21.30%	30.60%	23.60%	32.80%
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%