Accumulated Other Comprehensive Loss - Reclassification from Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains on securities transactions, net	$ 3		$ 217		$ 52	$ 595
Interest income	401,685		419,765		795,233	855,785
Tax effect	(22,907)		(51,759)		(56,080)	(108,924)
Total net of tax	70,424	$ 96,280	139,060	$ 146,551	166,704	285,611
Amortization of actuarial net loss	30,484		28,290		59,503	54,965
Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Out Of Accumulated Other Comprehensive Loss
Total net of tax	165		(524)		352	(911)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized Gains and Losses on AFS Securities
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains on securities transactions, net	(11)		0		(11)	0
Tax effect	3		0		3	0
Total net of tax	(8)		0		(8)	0
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized gains (losses) on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest income	299		(725)		597	(1,256)
Tax effect	(89)		209		(165)	361
Total net of tax	210		(516)		432	(895)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	13		3		27	6
Total net of tax	(37)		(8)		(72)	(16)
Amortization of actuarial net loss	$ (50)		$ (11)		$ (99)	$ (22)