Accumulated Other Comprehensive Loss - Reclassification from Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains (losses) on securities transactions, net	$ 47			$ (398)			$ 99	$ 197
Interest income	410,498			412,418			1,205,731	1,268,203
Tax effect	(28,818)			(53,486)			(84,898)	(162,410)
Total net of tax	97,856	$ 70,424	$ 96,280	141,346	$ 139,060	$ 146,551	264,560	426,957
Amortization of actuarial net loss	31,249			28,859			90,752	83,824
Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Out Of Accumulated Other Comprehensive Loss
Total net of tax	182			30			534	(881)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized Gains and Losses on AFS Securities
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains (losses) on securities transactions, net	(1)			(6)			(12)	(6)
Tax effect	0			1			3	1
Total net of tax	(1)			(5)			(9)	(5)
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	302			63			899	(1,193)
Tax effect	(83)			(20)			(248)	341
Total net of tax	219			43			651	(852)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	14			3			41	9
Total net of tax	(36)			(8)			(108)	(24)
Amortization of actuarial net loss	$ (50)			$ (11)			$ (149)	$ (33)