Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 275,860	$ 280,035	$ 280,035
Provision for loan losses	3,732	(336)
Loans charged off	(3,176)	(2,291)
Recoveries of loans previously charged off	1,303	1,186
Ending balance	277,719	278,594	275,860
Provision Details [Abstract]
Provision for credit losses	0	0
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	51,271	51,640	51,640
Provision for off-balance sheet credit risk	(5,934)	448
Ending balance	45,337	52,088	51,271
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	26,127,389		25,577,102
Individually measured for impairment, recorded investment	60,004		74,360
Total	26,187,393		25,651,462
Related allowance [Abstract]
Collectively measured for impairment, related allowance	274,638		269,672
Individually measured for impairment, related allowance	3,081		6,188
Total	277,719	278,594	275,860
Commercial [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	137,225	145,153	145,153
Provision for loan losses	(875)	(855)
Loans charged off	(1,435)	(1,085)
Recoveries of loans previously charged off	704	292
Ending balance	135,619	143,505	137,225
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	19,723	18,046	18,046
Provision for off-balance sheet credit risk	(1,779)	(1,879)
Ending balance	17,944	16,167	19,723
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	15,547,817		15,244,965
Individually measured for impairment, recorded investment	25,266		36,102
Total	15,573,083		15,281,067
Related allowance [Abstract]
Collectively measured for impairment, related allowance	132,538		133,232
Individually measured for impairment, related allowance	3,081		3,993
Total	135,619	143,505	137,225
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	86,120	91,072	91,072
Provision for loan losses	735	2,467
Loans charged off	0	0	(126)
Recoveries of loans previously charged off	18	185
Ending balance	86,873	93,724	86,120
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	30,086	31,959	31,959
Provision for off-balance sheet credit risk	(4,324)	1,502
Ending balance	25,762	33,461	30,086
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	5,878,078		5,665,309
Individually measured for impairment, recorded investment	6,601		6,697
Total	5,884,679		5,672,006
Related allowance [Abstract]
Collectively measured for impairment, related allowance	86,873		83,925
Individually measured for impairment, related allowance	0		2,195
Total	86,873	93,724	86,120
Loans to individuals [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	52,515	43,810	43,810
Provision for loan losses	3,872	(1,948)
Loans charged off	(1,741)	(1,206)
Recoveries of loans previously charged off	581	709
Ending balance	55,227	41,365	52,515
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	1,462	1,635	1,635
Provision for off-balance sheet credit risk	169	825
Ending balance	1,631	2,460	1,462
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	4,701,494		4,666,828
Individually measured for impairment, recorded investment	28,137		31,561
Total	4,729,631		4,698,389
Related allowance [Abstract]
Collectively measured for impairment, related allowance	55,227		52,515
Individually measured for impairment, related allowance	0		0
Total	$ 55,227	$ 41,365	$ 52,515

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Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

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