Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 26,730	$ 468	$ 139
State	5,632	1,259	1,398
Deferred:
Federal	92,441	4,045	(162)
State	32,179	135	(19)
Income tax expense	$ 156,982	$ 5,907	$ 1,356