Income Taxes - Components of Income Tax Expense (Benefit) Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax expense (benefit)
Federal income tax expense (benefit)	$ 0	$ 4,477	$ 32,422
State income tax expense (benefit)	2,408	1,340	1,764
Total current income tax expense (benefit)	2,408	5,817	34,186
Deferred income tax expense (benefit)
Federal income tax expense (benefit)	0	1,622	10,251
State income tax expense (benefit)	2,458	933	1,095
Total deferred income tax expense (benefit)	2,458	2,555	11,346
Total income tax expense (benefit)	$ 4,866	$ 8,372	$ 45,532