Income Taxes Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Computed Tax Expense at Statutory Rate	$ 13,949	$ 13,212	$ 12,345
Tax Cuts and Jobs Act impact on deferred remeasurement	(1,116)	0	0
Tax-Exempt Income	(2,537)	(2,437)	(2,292)
Nondeductible Interest Expense	52	40	36
State Taxes, Net of Federal Income Tax Benefit	698	554	805
Tax benefit from stock based compensation	(134)	0	0
Other Items, Net	(383)	(154)	(284)
Income Tax Expense (Benefit), Continuing Operations	10,529	$ 11,215	$ 10,610
Tax Cuts And Jobs Act Of 2017, deferred tax asset, provisional income tax expense	$ 1,100