Accumulated Other Comprehensive Income (Loss) - AOCI Components Pre Post & Tax Effect (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Other Comprehensive Income (Loss), Before Tax:
Net Unrealized Gains (Losses) Arising During the Period	$ (38,035)			$ (111,338)			$ (36,702)	$ (523,365)
(Gain) Loss on Sale	4,582						4,582
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	6,787			3,037			20,500	3,100
Net Unrealized Gains (Losses) on Investment Securities	(26,666)			(108,301)			(11,620)	(520,265)
Amortization of Net Actuarial Losses (Gains)	177			542			528	1,626
Amortization of Prior Service Credit	(62)			(61)			(184)	(184)
Defined Benefit Plans, Net	115			481			344	1,442
Other Comprehensive Income (Loss)	(26,551)			(107,820)			(11,276)	(518,823)
Other Comprehensive Income (Loss), Tax Effect:
Net Unrealized Gains (Losses) Arising During the Period	(11,439)			(29,506)			(11,086)	(138,715)
(Gain) Loss on Sale	1,237						1,237
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	1,800			805			5,434	821
Net Unrealized Gains (Losses) on Investment Securities	(8,402)			(28,701)			(4,415)	(137,894)
Amortization of Net Actuarial Losses (Gains)	46			143			140	431
Amortization of Prior Service Credit	(15)			(16)			(48)	(48)
Defined Benefit Plans, Net	31			127			92	383
Other Comprehensive Income (Loss)	(8,371)			(28,574)			(4,323)	(137,511)
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) Arising During the Period	(26,596)			(81,832)			(25,616)	(384,650)
(Gain) Loss on Sale	3,345						3,345
Amortization of Unrealized Holding (Gains) Losses on HTM Securities	4,987			2,232			15,066	2,279
Net Unrealized Gains (Losses) on Investment Securities	(18,264)			(79,600)			(7,205)	(382,371)
Amortization of Net Actuarial Losses (Gains)	131			399			388	1,195
Amortization of Prior Service Credit	(47)			(45)			(136)	(136)
Defined Benefit Plans, Net	84			354			252	1,059
Total Other Comprehensive Income (Loss)	$ (18,180)	$ (18,133)	$ 29,360	$ (79,246)	$ (122,295)	$ (179,771)	$ (6,953)	$ (381,312)

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