Income Taxes - Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax provision (benefit):
Federal	$ 5,853	$ (3,801)	$ 3,801
State	180	111	1,035
Total current payable	6,033	(3,690)	4,836
Deferred tax provision (benefit):
Federal	(166,890)	(77,430)	66,430
State	20,133	(6,106)	5,239
Total deferred payable	(146,757)	(83,536)	71,669
Provision (benefit) for income taxes	$ (140,724)	$ (87,226)	$ 76,505