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Allowance for Credit Losses - By Loan Class (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	$ 157,069	$ 125,972	$ 125,972
Losses charged to allowance	(27,824)	(2,033)
Recoveries credited to allowance	575	1,031
Net losses charged to allowance	(27,249)	(1,002)
Provision (credit) charged to operations	12,978	8,587
Balance at the end of the period	142,798	133,557	157,069
Commercial, financial and agricultural | Commercial.
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Charge-down due to customer filing bankruptcy	25,600
Impact on credit loss expense due to customer filing bankruptcy	4,400
Commercial, financial and agricultural | Domestic | Commercial.
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	35,550	26,728	26,728
Losses charged to allowance	(27,741)	(1,971)	(9,664)
Recoveries credited to allowance	555	625
Net losses charged to allowance	(27,186)	(1,346)
Provision (credit) charged to operations	18,312	2,406
Balance at the end of the period	26,676	27,788	35,550
Commercial, financial and agricultural | Domestic | Commercial real estate: farmland & commercial
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	42,703	36,474	36,474
Recoveries credited to allowance	4	5
Net losses charged to allowance	4	5
Provision (credit) charged to operations	(3,305)	77
Balance at the end of the period	39,402	36,556	42,703
Commercial, financial and agricultural | Domestic | Commercial real estate: multifamily
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	5,088	3,794	3,794
Provision (credit) charged to operations	(1,320)	190
Balance at the end of the period	3,768	3,984	5,088
Obligations of states and political subdivisions | Domestic | Commercial Real Estate: other construction and land development
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	55,291	44,684	44,684
Recoveries credited to allowance		311
Net losses charged to allowance		311
Provision (credit) charged to operations	(194)	5,938
Balance at the end of the period	55,097	50,933	55,291
Real estate - mortgage | Domestic | Residential: first lien
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	5,812	4,759	4,759
Losses charged to allowance	(45)		(43)
Recoveries credited to allowance	2	7
Net losses charged to allowance	(43)	7
Provision (credit) charged to operations	(12)	(207)
Balance at the end of the period	5,757	4,559	5,812
Real estate - mortgage | Domestic | Residential Junior Lien
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	11,024	8,284	8,284
Losses charged to allowance		(1)	(298)
Recoveries credited to allowance	9	77
Net losses charged to allowance	9	76
Provision (credit) charged to operations	(385)	(3)
Balance at the end of the period	10,648	8,357	11,024
Consumer | Domestic
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	318	281	281
Losses charged to allowance	(38)	(61)	(179)
Recoveries credited to allowance	5	6
Net losses charged to allowance	(33)	(55)
Provision (credit) charged to operations	28	65
Balance at the end of the period	313	291	318
Foreign. | Foreign
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	1,283	968	968
Provision (credit) charged to operations	(146)	121
Balance at the end of the period	$ 1,137	$ 1,089	$ 1,283

X

- Definition

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

+ References

No definition available.

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Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable, due to bankruptcy of customer.

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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
-URI https://asc.fasb.org//1943274/2147479344/326-20-45-1

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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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+ References

Reference 1: 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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+ 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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+ References

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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

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