Comprehensive Income/Loss (Comprehensive Income/(Loss) Presented Net of Taxes) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Equity [Abstract]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, before Tax		$ (9,159)	$ 31,981
Other Comprehensive Income (Loss), Derivative, Excluded Component, Increase (Decrease), after Adjustments, Tax		2,576	(8,997)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax		(6,583)	22,984
COMPREHENSIVE INCOME
Change in fair value of securities available for sale, pre tax amount		(10,361)	12,123
Change in fair value of securities available for sale, tax (expense) benefit		2,587	(2,776)
Change in fair value of securities available for sale, after tax amount		(7,774)	9,347
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax		0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax		0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		0	0
Change in fair value of securities available for sale, pre tax amount		(10,361)	12,123
Change in fair value of securities available for sale, tax (expense) benefit		2,587	(2,776)
Change in fair value of securities available for sale, after tax amount		(7,774)	9,347
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax		(4,779)	33,567
Other Comprehensive Income (Loss), Derivative, Excluded Component, Increase (Decrease), before Adjustments, Tax		1,344	(9,443)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax		(3,435)	24,124
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax		4,380	1,586
Other Comprehensive Income (Loss), Derivative, Excluded Component, Increase (Decrease), Adjustments, Tax		(1,232)	(446)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax		3,148	1,140
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax		653	(1,389)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax		(184)	391
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax		469	(998)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax		442	245
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, Tax		(124)	(69)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax		318	176
Amortization of certain costs included in net periodic retirement costs, pre tax amount		44	69
Amortization of certain costs included in net periodic retirement costs, tax (expense) benefit		(12)	(19)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax		32	50
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	[1]	1,139	(1,075)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	[1]	(320)	303
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	[1]	819	(772)
Total other comprehensive income, pre tax amount		(18,381)	43,029
Total other comprehensive income, tax (expense) benefit		4,843	(11,470)
Total other comprehensive income, after tax amount		(13,538)	31,559
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Loss on Termination of Derivatives, before Tax		0	0
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Loss on Termination of Derivatives, before Tax		$ 0	$ 0

[1] The amortization of prior service costs is included in the computation of net periodic pension cost as disclosed in Note 15 "Employee Benefit Plans" within the Notes to the Consolidated Financial Statements included in Item 8 of the Company's 2020 Form 10-K.