Comprehensive Income Changes in Accumulated Other Comprehensive Income By Component (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Loss	[1]	$ (5,436)	$ (6,256)	$ (7,972)	$ (7,166)
Other comprehensive income, before reclassifications, net of tax	[1]	2,437	745
Reclassification from Accumulated Other Comprehensive Income, net of tax	[1]	99	165
Other Comprehensive Income	[1]	2,536	910
Unrealized Gains and Losses on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Loss	[1]	3,066	3,339	629	2,539
Other comprehensive income, before reclassifications, net of tax		2,437	745
Reclassification from Accumulated Other Comprehensive Income, net of tax		0	55
Other Comprehensive Income	[1]	2,437	800
Amortization of Net Retirement Plan Actuarial Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Loss	[1]	(7,792)	(9,138)	(7,893)	(9,255)
Other comprehensive income, before reclassifications, net of tax	[1]	0	0
Reclassification from Accumulated Other Comprehensive Income, net of tax		101	117
Other Comprehensive Income	[1]	101	117
Accretion of Net Retirement Plan Prior Service Credit [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Loss	[1]	(710)	(457)	$ (708)	$ (450)
Other comprehensive income, before reclassifications, net of tax	[1]	0	0
Reclassification from Accumulated Other Comprehensive Income, net of tax		(2)	(7)
Other Comprehensive Income	[1]	$ (2)	$ (7)

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