Comprehensive Income Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Schedule of Comprehensive Income [Line Items]
Net Unrealized Securities Holding Gains 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, before Tax		(3,273)	252
Other Comprehensive Income, Tax		833	(98)
Other Comprehensive Income		(2,440)	154
Unrealized Gains and Losses on Available for Sale Securities
Schedule of Comprehensive Income [Line Items]
Net Unrealized Securities Holding Losses on Securities Available-for-Sale Arising During the Period Before Tax		(3,332)	77
Net Unrealized Securities Holding Losses on Securities Available-for-Sale Arising During the Period, Tax		847	(30)
Net Unrealized Securities Holding Gains Arising During the Period		(2,485)	47
Other Comprehensive Income	[1]	(2,485)	47
Amortization of Net Retirement Plan Actuarial Gain (Loss)
Schedule of Comprehensive Income [Line Items]
Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax		60	178
Reclassification From Accumulated Other Comprehensive Income Current Period Tax (Expense) Benefit		(14)	(69)
Amortization of Net Retirement Plan Actuarial Loss		46	109
Other Comprehensive Income	[1]	46	109
Accretion of Net Retirement Plan Prior Service (Cost) Credit
Schedule of Comprehensive Income [Line Items]
Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax		(1)	(3)
Reclassification From Accumulated Other Comprehensive Income Current Period Tax (Expense) Benefit		0	1
Accretion of Net Retirement Plan Prior Service Credit		(1)	(2)
Other Comprehensive Income	[1]	$ (1)	$ (2)

[1] All amounts are net of tax. Amounts in parentheses indicate debits.