Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 8,531	$ 6,631
Other Comprehensive Income, Net of Tax:
Net Unrealized Securities Holding Gains (Losses) Arising During the Period	(2,485)	47
Amortization of Net Retirement Plan Actuarial Loss	46	109
Accretion of Net Retirement Plan Prior Service Credit	(1)	(2)
Other Comprehensive Income (Loss)	(2,440)	154
Comprehensive Income	$ 6,091	$ 6,785