Accumulated Other Comprehensive Income (Loss) (Reclassifications out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	$ 13,752	$ 5,719	$ 33,547	$ 5,719
Amounts reclassified from accumulated other comprehensive income, net of tax	(5,663)	2,281	(16,082)	8,993
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	1,472	629	2,913	1,263
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(4,926)	(2,106)	(9,749)	(4,227)
Tax effect	3,163	1,315	7,716	1,315
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	13,752	5,719	33,547	5,719
Amounts reclassified from accumulated other comprehensive income, net of tax	(10,589)	(4,404)	(25,831)	(4,404)
Tax effect	3,163	1,315	7,716	1,315
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	10,589	4,404	25,831	4,404
Defined Benefit Pension Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses and prior service cost		(2,721)		(5,462)
Total before taxes	(6,398)	(2,735)	(12,662)	(5,490)
Amounts reclassified from accumulated other comprehensive income, net of tax	4,926	2,106	9,749	4,227
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax		(14)		(28)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	1,472	629	2,913	1,263
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(4,926)	(2,106)	(9,749)	(4,227)
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	$ 0	4,579	$ 0	9,170
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Before Tax		(5,947)		(11,909)
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Tax		1,368		2,739
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Net Of Tax		$ (4,579)		$ (9,170)