Income Taxes - Provision for Income Tax (Benefit) Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 7,418	$ (22,416)	$ (1,377)
State	48	(64)	(138)
Total	7,466	(22,480)	(1,515)
Deferred:
Federal	(23,512)	29,796	2,261
State	(1,835)	(169)	62
Total	(25,347)	29,627	2,323
Income tax (benefit) expense	$ (17,881)	$ 7,147	$ 808