Allowance for Credit Losses - By Loan Class (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	$ 148,609	$ 140,503	$ 157,069	$ 125,972	$ 125,972
Losses charged to allowance	(2,371)	(2,569)	(34,455)	(7,584)
Recoveries credited to allowance	1,259	596	3,134	2,739
Net (losses) recoveries charged to allowance	(1,112)	(1,973)	(31,321)	(4,845)
Credit loss expense	8,602	10,476	30,351	27,879
Balance at the end of the period	156,099	149,006	156,099	149,006	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			4,300
Commercial, financial and agricultural | Domestic | Commercial
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	27,255	27,645	35,550	26,728	26,728
Losses charged to allowance	(2,329)	(2,373)	(32,049)	(7,136)	(9,664)
Recoveries credited to allowance	1,231	518	3,020	1,699
Net (losses) recoveries charged to allowance	(1,098)	(1,855)	(29,029)	(5,437)
Credit loss expense	3,723	8,063	23,359	12,562
Balance at the end of the period	29,880	33,853	29,880	33,853	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	44,888	38,688	42,703	36,474	36,474
Recoveries credited to allowance	6	6	16	17
Net (losses) recoveries charged to allowance	6	6	16	17
Credit loss expense	(510)	3,190	1,665	5,393
Balance at the end of the period	44,384	41,884	44,384	41,884	42,703
Commercial, financial and agricultural | Domestic | Commercial Real Estate Multifamily Receivable [Member]
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	3,528	4,106	5,088	3,794	3,794
Credit loss expense	4	422	(1,556)	734
Balance at the end of the period	3,532	4,528	3,532	4,528	5,088
Real estate - construction | 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	54,840	53,064	55,291	44,684	44,684
Losses charged to allowance			(2,228)
Recoveries credited to allowance				837
Net (losses) recoveries charged to allowance			(2,228)	837
Credit loss expense	5,182	(1,967)	6,959	5,576
Balance at the end of the period	60,022	51,097	60,022	51,097	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	5,806	5,092	5,812	4,759	4,759
Losses charged to allowance		(43)	(46)	(43)	(43)
Recoveries credited to allowance	2	7	38	15
Net (losses) recoveries charged to allowance	2	(36)	(8)	(28)
Credit loss expense	214	481	218	806
Balance at the end of the period	6,022	5,537	6,022	5,537	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	10,639	10,442	11,024	8,284	8,284
Losses charged to allowance		(118)		(283)	(298)
Recoveries credited to allowance	13	63	48	155
Net (losses) recoveries charged to allowance	13	(55)	48	(128)
Credit loss expense	(70)	206	(490)	2,437
Balance at the end of the period	10,582	10,593	10,582	10,593	11,024
Consumer | Domestic
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	314	286	318	281	281
Losses charged to allowance	(42)	(35)	(132)	(122)	(179)
Recoveries credited to allowance	6	2	11	16
Net (losses) recoveries charged to allowance	(36)	(33)	(121)	(106)
Credit loss expense	14	45	95	123
Balance at the end of the period	292	298	292	298	318
Foreign | Foreign
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	1,339	1,180	1,283	968	968
Recoveries credited to allowance	1		1
Net (losses) recoveries charged to allowance	1		1
Credit loss expense	45	36	101	248
Balance at the end of the period	$ 1,385	$ 1,216	$ 1,385	$ 1,216	$ 1,283