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, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains (losses) on securities transactions, net	$ 217		$ (309)		$ 595	$ (1,381)
Tax effect	(51,759)		(36,552)		(108,924)	(75,866)
Net interest income	(419,765)		(418,160)		(855,785)	(735,829)
Net income	139,060	$ 146,551	96,413	$ 116,728	285,611	213,141
Amortization of actuarial net loss	28,290		22,284		54,965	37,646
Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Out Of Accumulated Other Comprehensive Loss
Net income	(524)		(53)		(911)	(561)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized gains on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains (losses) on securities transactions, net	0		0		0	14
Tax effect	0		0		0	(4)
Net income	0		0		0	10
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized gains (losses) on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	209		(36)		361	120
Net interest income	(725)		116		(1,256)	(426)
Net income	(516)		80		(895)	(306)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	3		51		6	102
Net income	(8)		(133)		(16)	(265)
Amortization of actuarial net loss	$ (11)		$ (184)		$ (22)	$ (367)