Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 40,676	$ 35,184	$ 30,064
Unrealized Gains (Losses) on Securities:
Unrealized Holding Gain (Loss) Arising During the Period	7,364	(13,830)	2,153
Reclassification Adjustment for Gains Included in Net Income	(596)	(1,979)	(725)
Tax Effect	(2,377)	5,607	(496)
Net of Tax	4,391	(10,202)	932
Defined Benefit Pension Plans and Postretirement Benefit Obligation
Net (Loss) Arising During the Period	(226)	(24)	(22)
Reclassification Adjustment for Amortization of Prior Service Cost and Net Loss Included in Net Periodic Pension Cost	8	6	5
Tax Effect	80	4	7
Net of Tax	(138)	(14)	(10)
Total Other Comprehensive Income (Loss)	4,253	(10,216)	922
COMPREHENSIVE INCOME	$ 44,929	$ 24,968	$ 30,986