Comprehensive Income Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Schedule of Comprehensive Income [Line Items]
Net Unrealized Securities Holding Gains Arising During the Period		$ 9	[1]	$ (810)	[1]	$ 465		$ 2,309	[1]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		6	[1]	0	[1]	6	[2]	88	[1]
Amortization of Net Retirement Plan Actuarial Loss		(64)	[1]	(111)	[1]	(245)		(314)	[1]
Accretion of Net Retirement Plan Prior Service Credit		2	[1]	1	[1]	5		5	[1]
Other Comprehensive Income, before Tax		172		(1,086)		1,268		4,220
Other Comprehensive Income, Tax		(107)		386		(569)		(1,690)
Other Comprehensive Income	[2]	65		(700)		699		2,530
Unrealized Gains and Losses on Available for Sale Securities
Schedule of Comprehensive Income [Line Items]
Other Comprehensive Income Gain (Loss) Before Reclassifications Before Tax		6		(1,264)		749		3,868
Other Comprehensive Income Gain (Loss) Before Reclassifications Tax (Expense) Benefit		3		454		(284)		(1,559)
Net Unrealized Securities Holding Gains Arising During the Period		9		(810)		465		2,309
Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax		(10)		0		(10)		(144)
Reclassification From Accumulated Other Comprehensive Income Current Period Tax (Expense) Benefit		4		0		4		56
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		(6)		0		(6)		(88)
Other Comprehensive Income		3		(810)		459		2,221
Amortization of Net Retirement Plan Actuarial Loss
Schedule of Comprehensive Income [Line Items]
Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax		179		181		537		503
Reclassification From Accumulated Other Comprehensive Income Current Period Tax (Expense) Benefit		(115)		(70)		(292)		(189)
Amortization of Net Retirement Plan Actuarial Loss		64		111		245		314
Other Comprehensive Income		64		111		245		314
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)		(3)		(8)		(7)
Reclassification From Accumulated Other Comprehensive Income Current Period Tax (Expense) Benefit		1		2		3		2
Accretion of Net Retirement Plan Prior Service Credit		(2)		(1)		(5)		(5)
Other Comprehensive Income		$ (2)		$ (1)		$ (5)		$ (5)

[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.