Accumulated Other Comprehensive Income (Loss) (Reclassifications out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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	$ 15,830	$ 13,752	$ 25,037	$ 33,547
Amounts reclassified from accumulated other comprehensive income, net of tax	(7,389)	(5,663)	(9,817)	(16,082)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	1,614	1,472	3,116	2,913
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(5,404)	(4,926)	(10,431)	(9,749)
Tax effect	3,641	3,163	5,759	7,716
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	15,830	13,752	25,037	33,547
Amounts reclassified from accumulated other comprehensive income, net of tax	(12,189)	(10,589)	(19,278)	(25,831)
Tax effect	3,641	3,163	5,759	7,716
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	12,189	10,589	19,278	25,831
Defined Benefit Pension Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before taxes	(7,018)	(6,398)	(13,547)	(12,662)
Amounts reclassified from accumulated other comprehensive income, net of tax	5,404	4,926	10,431	9,749
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	1,614	1,472	3,116	2,913
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(5,404)	(4,926)	(10,431)	(9,749)
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	(604)	$ 0	(970)	$ 0
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Before Tax	785		1,260
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Tax	(181)		(290)
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Net Of Tax	$ 604		$ 970