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Allowance for Credit Losses - By Loan Class (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period		$ 154,983	$ 148,609	$ 156,537	$ 157,069	$ 157,069
Losses charged to allowance		(2,025)	(2,371)	(14,002)	(34,455)
Recoveries credited to allowance		721	1,259	3,417	3,134
Net (losses) recoveries charged to allowance		(1,304)	(1,112)	(10,585)	(31,321)
Credit loss expense		1,827	8,602	9,554	30,351
Balance at the end of the period		155,506	156,099	155,506	156,099	156,537
Commercial, financial and agricultural | Commercial
Rollforward of transactions in the allowance for credit loan losses by loan class
Charge-down due to customer filing bankruptcy	$ 25,600
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		28,414	27,255	29,853	35,550	35,550
Losses charged to allowance		(1,968)	(2,329)	(5,505)	(32,049)	(34,149)
Recoveries credited to allowance		625	1,231	3,072	3,020
Net (losses) recoveries charged to allowance		(1,343)	(1,098)	(2,433)	(29,029)
Credit loss expense		1,585	3,723	1,236	23,359
Balance at the end of the period		28,656	29,880	28,656	29,880	29,853
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		46,660	44,888	43,990	42,703	42,703
Recoveries credited to allowance		71	6	183	16
Net (losses) recoveries charged to allowance		71	6	183	16
Credit loss expense		3,471	(510)	6,029	1,665
Balance at the end of the period		50,202	44,384	50,202	44,384	43,990
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		8,000	3,528	4,869	5,088	5,088
Credit loss expense		2,740	4	5,871	(1,556)
Balance at the end of the period		10,740	3,532	10,740	3,532	4,869
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		54,065	54,840	60,639	55,291	55,291
Losses charged to allowance				(8,121)	(2,228)	(2,228)
Net (losses) recoveries charged to allowance				(8,121)	(2,228)
Credit loss expense		(7,019)	5,182	(5,472)	6,959
Balance at the end of the period		47,046	60,022	47,046	60,022	60,639
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		6,242	5,806	5,528	5,812	5,812
Losses charged to allowance				(49)	(46)	(46)
Recoveries credited to allowance		9	2	24	38
Net (losses) recoveries charged to allowance		9	2	(25)	(8)
Credit loss expense		210	214	958	218
Balance at the end of the period		6,461	6,022	6,461	6,022	5,528
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		9,998	10,639	10,031	11,024	11,024
Losses charged to allowance		(1)		(203)
Recoveries credited to allowance		8	13	124	48
Net (losses) recoveries charged to allowance		7	13	(79)	48
Credit loss expense		(185)	(70)	(132)	(490)
Balance at the end of the period		9,820	10,582	9,820	10,582	10,031
Consumer | Domestic
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period		273	314	281	318	318
Losses charged to allowance		(56)	(42)	(124)	(132)	(185)
Recoveries credited to allowance		8	6	14	11
Net (losses) recoveries charged to allowance		(48)	(36)	(110)	(121)
Credit loss expense		46	14	100	95
Balance at the end of the period		271	292	271	292	281
Foreign | Foreign
Rollforward of transactions in the allowance for credit loan losses by loan class
Balance at the beginning of the period		1,331	1,339	1,346	1,283	1,283
Recoveries credited to allowance			1		1
Net (losses) recoveries charged to allowance			1		1
Credit loss expense		979	45	964	101
Balance at the end of the period		$ 2,310	$ 1,385	$ 2,310	$ 1,385	$ 1,346

X

- Definition

Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff due to bankruptcy of customer.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
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- Definition

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.

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

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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.

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

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