Comprehensive Income Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2017		Jun. 30, 2016		Jun. 30, 2017	Jun. 30, 2016
Schedule of Comprehensive Income [Line Items]
Net Unrealized Securities Holding Gains Arising During the Period		$ 409	[1]	$ 682	[1]	$ 456	$ 3,119	[1]
Amortization of Net Retirement Plan Actuarial Loss		72	[1]	102	[1]	181	203	[1]
Accretion of Net Retirement Plan Prior Service Credit		(1)	[1]	(2)	[1]	(3)	(4)	[1]
Other Comprehensive Income, before Tax		844		1,143		1,096	5,315
Other Comprehensive Income, Tax		(364)		(449)		(462)	(2,085)
Other Comprehensive Income	[2]	480		694		634	3,230
Unrealized Gains and Losses on Available for Sale Securities
Schedule of Comprehensive Income [Line Items]
Other Comprehensive Income Gain (Loss) Before Reclassifications Before Tax		666		1,123		743	5,132
Other Comprehensive Income Gain (Loss) Before Reclassifications Tax (Expense) Benefit		(257)		(441)		(287)	(2,013)
Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax				(144)			(144)
Reclassification From Accumulated Other Comprehensive Income Current Period Tax (Expense) Benefit				56			56
Other Comprehensive Income	[1]	409		594		456	3,031
Amortization of Net Retirement Plan Actuarial Loss
Schedule of Comprehensive Income [Line Items]
Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax		181		168		359	334
Reclassification From Accumulated Other Comprehensive Income Current Period Tax (Expense) Benefit		(109)		(66)		(178)	(131)
Other Comprehensive Income	[1]	72		102		181	203
Accretion of Net Retirement Plan Prior Service Credit
Schedule of Comprehensive Income [Line Items]
Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax		(3)		(4)		(6)	(7)
Reclassification From Accumulated Other Comprehensive Income Current Period Tax (Expense) Benefit		2		2		3	3
Other Comprehensive Income	[1]	$ (1)		$ (2)		$ (3)	$ (4)

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

[2] These accumulated other comprehensive income components are included in the computation of net periodic pension cost.