Allowance for Credit Losses - Roll Forward Of the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2021
Allowance for loan losses:
Beginning balance	$ 164,171	$ 176,144
Charge-offs	(3,057)	(5,370)
Recoveries	2,206	2,332
Net (charge-offs) recoveries	(851)	(3,038)
Provision for credit losses on loans	1,500	0	$ 0
Ending balance	166,468	173,106
Individually evaluated	12,851	15,593
Collectively evaluated	153,617	157,513
Loans:
Individually evaluated	33,581	40,875
Collectively evaluated	10,279,878	10,647,533
Gross loans	10,313,459	10,688,408		$ 10,020,914
Nonaccruing loans with no allowance for credit losses	8,349	8,656
Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	33,922	39,031
Charge-offs	(2,102)	(3,498)
Recoveries	1,136	289
Net (charge-offs) recoveries	(966)	(3,209)
Provision for credit losses on loans	(998)	1,770
Ending balance	33,606	37,592
Individually evaluated	9,225	9,908
Collectively evaluated	24,381	27,684
Loans:
Individually evaluated	13,070	15,435
Collectively evaluated	1,432,537	2,233,852
Gross loans	1,445,607	2,249,287
Nonaccruing loans with no allowance for credit losses	435	1,848
Real estate – construction:
Allowance for loan losses:
Beginning balance	16,419	16,047
Charge-offs	0	(52)
Recoveries	0	13
Net (charge-offs) recoveries	0	(39)
Provision for credit losses on loans	1,992	(1,031)
Ending balance	18,411	14,977
Individually evaluated	0	0
Collectively evaluated	18,411	14,977
Loans:
Individually evaluated	0	0
Collectively evaluated	1,222,052	955,918
Gross loans	1,222,052	955,918
Nonaccruing loans with no allowance for credit losses	0	0
Real estate – 1-4 family mortgage:
Allowance for loan losses:
Beginning balance	32,356	32,165
Charge-offs	(163)	(101)
Recoveries	178	261
Net (charge-offs) recoveries	15	160
Provision for credit losses on loans	4,477	(631)
Ending balance	36,848	31,694
Individually evaluated	396	232
Collectively evaluated	36,452	31,462
Loans:
Individually evaluated	4,477	6,311
Collectively evaluated	2,836,502	2,679,750
Gross loans	2,840,979	2,686,061
Nonaccruing loans with no allowance for credit losses	2,614	4,695
Real estate – commercial mortgage:
Allowance for loan losses:
Beginning balance	68,940	76,127
Charge-offs	(6)	(61)
Recoveries	155	171
Net (charge-offs) recoveries	149	110
Provision for credit losses on loans	(3,858)	(12)
Ending balance	65,231	76,225
Individually evaluated	2,660	4,846
Collectively evaluated	62,571	71,379
Loans:
Individually evaluated	15,464	18,508
Collectively evaluated	4,562,400	4,530,519
Gross loans	4,577,864	4,549,027
Nonaccruing loans with no allowance for credit losses	5,298	2,113
Lease financing
Allowance for loan losses:
Beginning balance	1,486	1,624
Charge-offs	(7)	0
Recoveries	12	11
Net (charge-offs) recoveries	5	11
Provision for credit losses on loans	91	(89)
Ending balance	1,582	1,546
Individually evaluated	0	0
Collectively evaluated	1,582	1,546
Loans:
Individually evaluated	0	0
Collectively evaluated	89,842	75,256
Gross loans	89,842	75,256
Nonaccruing loans with no allowance for credit losses	0	0
Installment Loans to Individuals
Allowance for loan losses:
Beginning balance	11,048	11,150
Charge-offs	(779)	(1,658)
Recoveries	725	1,587
Net (charge-offs) recoveries	(54)	(71)
Provision for credit losses on loans	(204)	(7)
Ending balance	10,790	11,072
Individually evaluated	570	607
Collectively evaluated	10,220	10,465
Loans:
Individually evaluated	570	621
Collectively evaluated	136,545	172,238
Gross loans	137,115	172,859
Nonaccruing loans with no allowance for credit losses	2	$ 0
Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses:
Beginning balance	1,648
Cumulative Effect, Period Of Adoption, Adjustment | Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	1,648
Cumulative Effect, Period Of Adoption, Adjustment | Real estate – construction:
Allowance for loan losses:
Beginning balance	0
Cumulative Effect, Period Of Adoption, Adjustment | Real estate – 1-4 family mortgage:
Allowance for loan losses:
Beginning balance	0
Cumulative Effect, Period Of Adoption, Adjustment | Real estate – commercial mortgage:
Allowance for loan losses:
Beginning balance	0
Cumulative Effect, Period Of Adoption, Adjustment | Lease financing
Allowance for loan losses:
Beginning balance	0
Cumulative Effect, Period Of Adoption, Adjustment | Installment Loans to Individuals
Allowance for loan losses:
Beginning balance	$ 0