Accumulated Other Comprehensive Income (Loss) - AOCI Components Pre Post & Tax Effect (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Comprehensive Income (Loss), Before Tax:
Net Unrealized Gains (Losses) Arising During the Period	$ (6,771)			$ 7,314			$ 60,177	$ 38,077
(Gain) Loss on sale, before tax							(77)	(63)
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	104			39			289	804
Net Unrealized Gains (Losses) on Investment Securities	(6,667)			7,353			60,389	38,818
Amortization of Net Actuarial Losses (Gains)	570			406			1,711	1,218
Amortization of Prior Service Credit	(61)			(72)			(184)	(216)
Defined Benefit Plans, Net	509			334			1,527	1,002
Other Comprehensive Income (Loss)	(6,158)			7,687			61,916	39,820
Other Comprehensive Income (Loss), Tax Effect:
Net Unrealized Gains (Losses) Arising During the Period	(1,795)			1,938			15,945	10,090
(Gain) Loss on Sale, Tax Effect							(21)	(17)
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	28			10			76	212
Net Unrealized Gains (Losses) on Investment Securities	(1,767)			1,948			16,000	10,285
Amortization of Net Actuarial Losses (Gains)	151			108			454	323
Amortization of Prior Service Credit	(16)			(19)			(49)	(57)
Defined Benefit Plans, Net	135			89			405	266
Other Comprehensive Income (Loss)	(1,632)			2,037			16,405	10,551
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) Arising During the Period	(4,976)			5,376			44,232	27,987
(Gain) Loss on sale, Net of Tax							(56)	(46)
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	76			29			213	592
Net Unrealized Gains (Losses) on Investment Securities	(4,900)			5,405			44,389	28,533
Amortization of Net Actuarial Losses (Gains)	419			298			1,257	895
Amortization of Prior Service Credit	(45)			(53)			(135)	(159)
Defined Benefit Plans, Net	374			245			1,122	736
Total Other Comprehensive Income (Loss)	$ (4,526)	$ 8,104	$ 41,933	$ 5,650	$ 16,454	$ 7,165	$ 45,511	$ 29,269