Accumulated Other Comprehensive Loss - Reclassifications from AOCI (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Out Of Accumulated Other Comprehensive Loss
Losses on securities transactions, net	$ (46)			$ (93)			$ (127)	$ (114)
Tax effect	(38,891)			(25,307)			(101,486)	(110,035)
Total net of tax	102,374	$ 95,601	$ 87,268	81,891	$ 76,468	$ 113,330	285,243	271,689
Interest expense	(54,257)			(108,636)			(218,677)	(317,720)
Total reclassifications, net of tax	(1,334)			(452)			(1,866)	(1,062)
Unrealized losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(36)						(94)
Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(1,127)						(1,257)
Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of actuarial net loss	(234)			(79)			(699)	(235)
Tax effect	63			23			184	69
Total reclassifications, net of tax	(171)			(56)			(515)	(166)
Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(1,586)			(453)			(1,763)	(1,126)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Losses on securities transactions, net	(46)			(93)			(127)	(114)
Tax effect	10			21			33	24
Total net of tax	(36)			(72)			(94)	(90)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	459			129			506	320
Total net of tax	(1,127)			(324)			(1,257)	(806)
Interest expense	$ (1,586)			$ (453)			$ (1,763)	$ (1,126)