Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive loss	$ (10,419)	$ 6,712
Net current period other comprehensive income	101,111	28,327
Unrealized Losses on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	5,792
Net unrealized gains arising during period	111,530	21,615
Amounts reclassified from accumulated other comprehensive loss	(15,242)	0
Net current period other comprehensive income	96,288	21,615
Ending balance	102,080	(16,890)
Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	0
Net unrealized gains arising during period	0	0
Amounts reclassified from accumulated other comprehensive loss	0	4,591
Net current period other comprehensive income	0	4,591
Ending balance	0	(66,558)
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(132,515)
Net unrealized gains arising during period	0	0
Amounts reclassified from accumulated other comprehensive loss	4,823	2,121
Net current period other comprehensive income	4,823	2,121
Ending balance	(127,692)	(123,412)
Accumulated Other Comprehensive (Loss) Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(126,723)
Net unrealized gains arising during period	111,530	21,615
Amounts reclassified from accumulated other comprehensive loss	(10,419)	6,712
Net current period other comprehensive income	101,111	28,327
Ending balance	$ (25,612)	(206,860)
Previously Reported | Unrealized Losses on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(38,505)
Previously Reported | Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(71,149)
Previously Reported | Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(125,533)
Previously Reported | Accumulated Other Comprehensive (Loss) Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ (235,187)