LOANS AND ALLOWANCE FOR CREDIT LOSSES - Analysis of Past-Due Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Total Loans	$ 14,824,539	$ 14,480,925
Loans 90 Days or More Past Due and Still Accruing	7,472	8,326
Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	110,052	134,659
Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	46,803	56,483
Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	17,180	13,582
Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	46,069	64,594
Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	14,714,487	14,346,266
Commercial, financial and agricultural
Financing Receivable, Past Due [Line Items]
Total Loans	1,217,575	1,627,477
Loans 90 Days or More Past Due and Still Accruing	2	0
Commercial, financial and agricultural | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	5,900	12,246
Commercial, financial and agricultural | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	2,271	4,576
Commercial, financial and agricultural | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,569	2,018
Commercial, financial and agricultural | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	2,060	5,652
Commercial, financial and agricultural | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	1,211,675	1,615,231
Consumer installment
Financing Receivable, Past Due [Line Items]
Total Loans	207,111	306,995
Loans 90 Days or More Past Due and Still Accruing	569	1,755
Consumer installment | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	3,263	5,621
Consumer installment | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,549	2,189
Consumer installment | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	804	1,114
Consumer installment | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	910	2,318
Consumer installment | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	203,848	301,374
Indirect automobile
Financing Receivable, Past Due [Line Items]
Total Loans	325,057	580,083
Loans 90 Days or More Past Due and Still Accruing	0	0
Indirect automobile | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,498	6,470
Indirect automobile | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	699	3,293
Indirect automobile | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	284	1,006
Indirect automobile | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	515	2,171
Indirect automobile | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	323,559	573,613
Mortgage warehouse
Financing Receivable, Past Due [Line Items]
Total Loans	768,577	916,353
Loans 90 Days or More Past Due and Still Accruing	0	0
Mortgage warehouse | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Mortgage warehouse | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Mortgage warehouse | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Mortgage warehouse | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Mortgage warehouse | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	768,577	916,353
Municipal
Financing Receivable, Past Due [Line Items]
Total Loans	624,430	659,403
Loans 90 Days or More Past Due and Still Accruing	0	0
Municipal | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Municipal | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Municipal | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Municipal | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Municipal | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	624,430	659,403
Premium finance
Financing Receivable, Past Due [Line Items]
Total Loans	840,737	687,841
Loans 90 Days or More Past Due and Still Accruing	5,881	6,571
Premium finance | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	18,112	17,654
Premium finance | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	7,264	7,188
Premium finance | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	4,967	3,895
Premium finance | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	5,881	6,571
Premium finance | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	822,625	670,187
Real estate – construction and development
Financing Receivable, Past Due [Line Items]
Total Loans	1,454,824	1,606,710
Loans 90 Days or More Past Due and Still Accruing	1,020	0
Real estate – construction and development | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	27,370	19,221
Real estate – construction and development | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	22,290	13,348
Real estate – construction and development | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	3,181	723
Real estate – construction and development | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,899	5,150
Real estate – construction and development | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	1,427,454	1,587,489
Real estate – commercial and farmland
Financing Receivable, Past Due [Line Items]
Total Loans	6,409,704	5,300,006
Loans 90 Days or More Past Due and Still Accruing	0	0
Real estate – commercial and farmland | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	16,949	15,722
Real estate – commercial and farmland | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	9,373	5,370
Real estate – commercial and farmland | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,166	1,701
Real estate – commercial and farmland | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	6,410	8,651
Real estate – commercial and farmland | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	6,392,755	5,284,284
Real estate – residential
Financing Receivable, Past Due [Line Items]
Total Loans	2,976,524	2,796,057
Loans 90 Days or More Past Due and Still Accruing	0	0
Real estate – residential | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	36,960	57,725
Real estate – residential | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	3,357	20,519
Real estate – residential | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	5,209	3,125
Real estate – residential | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	28,394	34,081
Real estate – residential | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	$ 2,939,564	$ 2,738,332