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, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Out Of Accumulated Other Comprehensive Loss
Unrealized (losses) gains on AFS securities before tax	$ (398)			$ 323			$ 197	$ (1,058)
Tax effect	(53,486)			(68,405)			(162,410)	(144,271)
Total net of tax	141,346	$ 139,060	$ 146,551	178,119	$ 96,413	$ 116,728	426,957	391,260
Interest income, interest expense	412,418			453,992			1,268,203	1,189,821
Amortization of actuarial net loss	28,859			22,683			83,824	60,329
Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Out Of Accumulated Other Comprehensive Loss
Total net of tax	30			(107)			(881)	(668)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized (losses) gains on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Unrealized (losses) gains on AFS securities before tax	(6)			16			(6)	30
Tax effect	1			(4)			1	(8)
Total net of tax	(5)			12			(5)	22
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	(20)			(8)			341	112
Total net of tax	43			13			(852)	(293)
Interest income, interest expense	63			21			(1,193)	(405)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	3			51			9	153
Total net of tax	(8)			(132)			(24)	(397)
Amortization of actuarial net loss	$ (11)			$ (183)			$ (33)	$ (550)