Allowance for Credit Losses (By Loan Class) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	$ 112,572	$ 108,281	$ 110,374	$ 109,059
Losses charged to allowance	(2,626)	(2,430)	(7,047)	(6,631)
Recoveries credited to allowance	724	673	2,127	1,760
Net (losses) recoveries charged to allowance	(1,902)	(1,757)	(4,920)	(4,871)
Credit loss expense	8,525	2,801	13,741	5,137
Balance at the end of the period	119,195	109,325	119,195	109,325
Commercial, financial and agricultural | Domestic | Commercial.
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	25,577	23,063	23,178	21,908
Losses charged to allowance	(2,568)	(2,287)	(6,681)	(5,835)
Recoveries credited to allowance	562	473	1,672	1,429
Net (losses) recoveries charged to allowance	(2,006)	(1,814)	(5,009)	(4,406)
Credit loss expense	1,273	1,955	6,675	5,702
Balance at the end of the period	24,844	23,204	24,844	23,204
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	35,270	34,238	35,654	30,000
Losses charged to allowance				(356)
Recoveries credited to allowance	7	141	21	160
Net (losses) recoveries charged to allowance	7	141	21	(196)
Credit loss expense	(303)	871	(701)	5,446
Balance at the end of the period	34,974	35,250	34,974	35,250
Commercial, financial and agricultural | Domestic | Commercial real estate: multifamily
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	2,856	4,206	3,291	5,051
Credit loss expense	237	9	(198)	(836)
Balance at the end of the period	3,093	4,215	3,093	4,215
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	36,713	33,603	35,390	37,612
Losses charged to allowance		(2)	(2)	(2)
Recoveries credited to allowance	100		103
Net (losses) recoveries charged to allowance	100	(2)	101	(2)
Credit loss expense	5,255	503	6,577	(3,506)
Balance at the end of the period	42,068	34,104	42,068	34,104
Real estate - mortgage | Domestic | Residential: first lien
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	4,137	3,916	4,073	3,874
Losses charged to allowance	(3)	(73)	(159)	(262)
Recoveries credited to allowance	13	12	211	47
Net (losses) recoveries charged to allowance	10	(61)	52	(215)
Credit loss expense	540	(110)	562	86
Balance at the end of the period	4,687	3,745	4,687	3,745
Real estate - mortgage | Domestic | Residential Junior Lien
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	6,894	8,196	7,754	9,570
Losses charged to allowance		(4)	(28)	(25)
Recoveries credited to allowance	27	28	89	86
Net (losses) recoveries charged to allowance	27	24	61	61
Credit loss expense	1,351	(496)	457	(1,907)
Balance at the end of the period	8,272	7,724	8,272	7,724
Consumer | Domestic
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	270	268	272	291
Losses charged to allowance	(55)	(64)	(177)	(151)
Recoveries credited to allowance	15	19	31	38
Net (losses) recoveries charged to allowance	(40)	(45)	(146)	(113)
Credit loss expense	62	47	166	92
Balance at the end of the period	292	270	292	270
Foreign. | Foreign
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at the beginning of the period	855	791	762	753
Credit loss expense	110	22	203	60
Balance at the end of the period	$ 965	$ 813	$ 965	$ 813