Income Tax - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 12,487	$ 13,493	$ 14,868
State	539	640	896
Total current taxes	13,026	14,133	15,764
Deferred:
Federal	1,467	6,279	5,344
State	766	1,731	1,186
Total deferred taxes	2,233	8,010	6,530
Total income tax expense	$ 15,259	$ 22,143	$ 22,294