Income Taxes - Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Federal
Current expense, federal	$ 5,677	$ 14,627	$ 3,736
Tax credit/ true-up, federal	(5,573)	(312)	274
Change in deferred benefit, federal	1,700	(369)	7,016
Income tax expense, federal	1,804	13,946	11,026
State
Current expense, state	1,662	2,368	1,640
Tax credit/ true-up, state	(383)	0	0
Change in deferred benefit, state	542	(467)	(1,518)
Income tax expense, state	1,821	1,901	122
Current expense, total	7,339	16,995	5,376
Tax credit/ true-up, total	(5,956)	(312)	274
Change in deferred benefit, total	2,242	(836)	5,498
Total provision	$ 3,625	$ 15,847	$ 11,148