Accumulated Other Comprehensive Income (Loss) - AOCI Components Pre Post & Tax Effect (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Other Comprehensive Income (Loss), Before Tax:
Net Unrealized Gains (Losses) Arising During the Period	$ (10,263)			$ (6,771)			$ (75,360)	$ 60,177
(Gain) Loss on sale, before tax	(83)						(3,758)	(77)
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	87			103			593	289
Net Unrealized Gains (Losses) on Investment Securities	(10,259)			(6,668)			(78,525)	60,389
Amortization of Net Actuarial Losses (Gains)	662			570			1,985	1,711
Amortization of Prior Service Credit	(62)			(61)			(185)	(184)
Defined Benefit Plans, Net	600			509			1,800	1,527
Other Comprehensive Income (Loss)	(9,659)			(6,159)			(76,725)	61,916
Other Comprehensive Income (Loss), Tax Effect:
Net Unrealized Gains (Losses) Arising During the Period	(2,719)			(1,795)			(19,954)	15,945
(Gain) Loss on Sale, Tax Effect	(22)						(1,014)	(21)
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	23			27			157	76
Net Unrealized Gains (Losses) on Investment Securities	(2,718)			(1,768)			(20,811)	16,000
Amortization of Net Actuarial Losses (Gains)	175			151			525	454
Amortization of Prior Service Credit	(16)			(16)			(49)	(49)
Defined Benefit Plans, Net	159			135			476	405
Other Comprehensive Income (Loss)	(2,559)			(1,633)			(20,335)	16,405
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) Arising During the Period	(7,544)			(4,976)			(55,406)	44,232
(Gain) Loss on Sale	(61)						(2,744)	(56)
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	64			76			436	213
Net Unrealized Gains (Losses) on Investment Securities	(7,541)			(4,900)			(57,714)	44,389
Amortization of Net Actuarial Losses (Gains)	487			419			1,460	1,257
Amortization of Prior Service Credit	(46)			(45)			(136)	(135)
Defined Benefit Plans, Net	441			374			1,324	1,122
Total Other Comprehensive Income (Loss)	$ (7,100)	$ 319	$ (49,609)	$ (4,526)	$ 8,104	$ 41,933	$ (56,390)	$ 45,511