Allowance for Credit Losses (By Loan Class) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	$ 110,227	$ 108,408	$ 110,374	$ 109,059
Losses charged to allowance	(2,092)	(1,848)	(4,421)	(4,201)
Recoveries credited to allowance	702	577	1,403	1,087
Net (losses) recoveries charged to allowance	(1,390)	(1,271)	(3,018)	(3,114)
Credit loss expense	3,735	1,144	5,216	2,336
Balance at the end of the period	112,572	108,281	112,572	108,281
Commercial, financial and agricultural | Domestic | Commercial.
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	23,901	22,163	23,178	21,908
Losses charged to allowance	(2,001)	(1,655)	(4,113)	(3,548)
Recoveries credited to allowance	508	498	1,110	956
Net (losses) recoveries charged to allowance	(1,493)	(1,157)	(3,003)	(2,592)
Credit loss expense	3,169	2,057	5,402	3,747
Balance at the end of the period	25,577	23,063	25,577	23,063
Commercial, financial and agricultural | Domestic | Commercial real estate: farmland & commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	34,854	32,203	35,654	30,000
Losses charged to allowance				(356)
Recoveries credited to allowance	6	7	14	19
Net (losses) recoveries charged to allowance	6	7	14	(337)
Credit loss expense	410	2,028	(398)	4,575
Balance at the end of the period	35,270	34,238	35,270	34,238
Commercial, financial and agricultural | Domestic | Commercial real estate: multifamily
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	3,062	5,935	3,291	5,051
Credit loss expense	(206)	(1,729)	(435)	(845)
Balance at the end of the period	2,856	4,206	2,856	4,206
Obligations of states and political subdivisions | Domestic | Commercial Real Estate: other construction and land development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	36,372	34,406	35,390	37,612
Losses charged to allowance			(2)
Recoveries credited to allowance	1		3
Net (losses) recoveries charged to allowance	1		1
Credit loss expense	340	(803)	1,322	(4,009)
Balance at the end of the period	36,713	33,603	36,713	33,603
Real estate - mortgage | Domestic | Residential: first lien
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	4,016	3,917	4,073	3,874
Losses charged to allowance	(57)	(117)	(156)	(189)
Recoveries credited to allowance	168	24	198	35
Net (losses) recoveries charged to allowance	111	(93)	42	(154)
Credit loss expense	10	92	22	196
Balance at the end of the period	4,137	3,916	4,137	3,916
Real estate - mortgage | Domestic | Residential Junior Lien
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	7,046	8,736	7,754	9,570
Losses charged to allowance		(21)	(28)	(21)
Recoveries credited to allowance	14	37	62	58
Net (losses) recoveries charged to allowance	14	16	34	37
Credit loss expense	(166)	(556)	(894)	(1,411)
Balance at the end of the period	6,894	8,196	6,894	8,196
Consumer | Domestic
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	264	279	272	291
Losses charged to allowance	(34)	(55)	(122)	(87)
Recoveries credited to allowance	5	11	16	19
Net (losses) recoveries charged to allowance	(29)	(44)	(106)	(68)
Credit loss expense	35	33	104	45
Balance at the end of the period	270	268	270	268
Foreign. | Foreign
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	712	769	762	753
Credit loss expense	143	22	93	38
Balance at the end of the period	$ 855	$ 791	$ 855	$ 791