Income Taxes - Income Tax (Benefit) (Details) $ in Thousands		3 Months Ended								12 Months Ended
	Dec. 22, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2018	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Currently payable tax:
Federal											$ 12,948	$ 13,373	$ 5,445
State											4,653	4,748	2,544
Total currently payable											17,601	18,121	7,989
Tax Cuts and Jobs Act of 2017 effect on re-measurement of net deferred tax assets	$ 7,103	$ 7,103									$ 7,103
Number of items for which the Company was unable to make a reasonable estimate for the effects of the tax law change | item											0
Deferred tax (benefit):
Federal											$ 1,193	(1,029)	2,029
Due to enactment of Tax Reform	$ 7,103	7,103									7,103
State											574	(504)	86
Total deferred tax											8,870	(1,533)	2,115
Income tax expense		$ 12,719	$ 5,249	$ 4,569	$ 3,934	$ 4,431	$ 4,054	$ 4,377	$ 3,726		$ 26,471	$ 16,588	$ 10,104
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate											35.00%	35.00%	35.00%
Forecast
Deferred tax (benefit):
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate										21.00%