Allowance for Credit Losses - By Loan Class (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	$ 170,014	$ 154,983	$ 159,174	$ 156,537	$ 156,537
Losses charged to allowance	(2,392)	(2,025)	(7,087)	(14,002)
Recoveries credited to allowance	709	721	2,115	3,417
Net (losses) recoveries charged to allowance	(1,683)	(1,304)	(4,972)	(10,585)
Provision (credit) charged to operations	1,625	1,827	15,754	9,554
Balance at the end of the period	169,956	155,506	169,956	155,506	159,174
Commercial, financial and agricultural \| Domestic \| Commercial
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	35,011	28,414	27,929	29,853	29,853
Losses charged to allowance	(1,954)	(1,968)	(6,189)	(5,505)	(7,673)
Recoveries credited to allowance	634	625	1,853	3,072
Net (losses) recoveries charged to allowance	(1,320)	(1,343)	(4,336)	(2,433)
Provision (credit) charged to operations	3,197	1,585	13,295	1,236
Balance at the end of the period	36,888	28,656	36,888	28,656	27,929
Commercial, financial and agricultural \| Domestic \| Commercial real estate: farmland & commercial
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	47,016	46,660	46,413	43,990	43,990
Losses charged to allowance	(47)		(47)
Recoveries credited to allowance	8	71	8	183
Net (losses) recoveries charged to allowance	(39)	71	(39)	183
Provision (credit) charged to operations	(2,685)	3,471	(2,082)	6,029
Balance at the end of the period	44,292	50,202	44,292	50,202	46,413
Commercial, financial and agricultural \| Domestic \| Commercial Real Estate Multifamily Receivable [Member]
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	18,355	8,000	14,713	4,869	4,869
Provision (credit) charged to operations	1,091	2,740	4,733	5,871
Balance at the end of the period	19,446	10,740	19,446	10,740	14,713
Commercial real estate \| Domestic \| Commercial
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period			48,907	60,639	60,639
Losses charged to allowance				(8,121)
Net (losses) recoveries charged to allowance				(8,121)
Provision (credit) charged to operations			(57)	(5,472)
Balance at the end of the period	48,850	47,046	48,850	47,046	48,907
Commercial real estate \| Domestic \| Commercial real estate construction development
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	48,563	54,065
Losses charged to allowance					(8,122)
Provision (credit) charged to operations	287	(7,019)
Balance at the end of the period	48,850	47,046	48,850	47,046
Real estate - mortgage \| Domestic \| Residential First Lien
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	7,034	6,242	6,725	5,528	5,528
Losses charged to allowance	(165)		(369)	(49)	(104)
Recoveries credited to allowance		9	142	24
Net (losses) recoveries charged to allowance	(165)	9	(227)	(25)
Provision (credit) charged to operations	312	210	683	958
Balance at the end of the period	7,181	6,461	7,181	6,461	6,725
Real estate - mortgage \| Domestic \| Residential Junior Lien
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	8,929	9,998	9,420	10,031	10,031
Losses charged to allowance	(105)	(1)	(218)	(203)	(260)
Recoveries credited to allowance	65	8	106	124
Net (losses) recoveries charged to allowance	(40)	7	(112)	(79)
Provision (credit) charged to operations	(192)	(185)	(611)	(132)
Balance at the end of the period	8,697	9,820	8,697	9,820	9,420
Consumer \| Domestic
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	251	273	279	281	281
Losses charged to allowance	(121)	(56)	(264)	(124)	(200)
Recoveries credited to allowance	2	8	6	14
Net (losses) recoveries charged to allowance	(119)	(48)	(258)	(110)
Provision (credit) charged to operations	114	46	225	100
Balance at the end of the period	246	271	246	271	279
Foreign \| Foreign
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period	4,855	1,331	4,788	1,346	1,346
Provision (credit) charged to operations	(499)	979	(432)	964
Balance at the end of the period	$ 4,356	$ 2,310	$ 4,356	$ 2,310	$ 4,788

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

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Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

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Amount, excluding accrued interest, of decrease (increase) in allowance for credit loss on financing receivable from writeoff (recovery). Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
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