Accumulated Other Comprehensive Income (Loss) (Reclassifications out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	$ 8,082	$ 21,425	$ 33,119	$ 54,972
Amounts reclassified from accumulated other comprehensive income, net of tax	(1,340)	(11,622)	(11,157)	(27,704)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	1,558	1,457	4,674	4,370
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(5,215)	(4,875)	(15,646)	(14,624)
Tax effect	1,858	4,928	7,617	12,644
Unrealized Losses on Investment Securities Available for Sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	8,082	21,425	33,119	54,972
Amounts reclassified from accumulated other comprehensive income, net of tax	(6,224)	(16,497)	(25,502)	(42,328)
Tax effect	1,858	4,928	7,617	12,644
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	6,224	16,497	25,502	42,328
Defined Benefit Pension Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before taxes	(6,773)	(6,332)	(20,320)	(18,994)
Amounts reclassified from accumulated other comprehensive income, net of tax	5,215	4,875	15,646	14,624
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	1,558	1,457	4,674	4,370
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(5,215)	(4,875)	(15,646)	(14,624)
Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive income, net of tax	(331)	$ 0	(1,301)	$ 0
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Before Tax	430		1,690
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Tax	(99)		(389)
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Net Of Tax	$ 331		$ 1,301