LOANS AND ALLOWANCE FOR CREDIT LOSSES - Analysis of Past-Due Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Total Loans	$ 14,780,791	$ 14,480,925
Loans 90 Days or More Past Due and Still Accruing	4,874	8,326
Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	96,192	134,659
Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	39,025	56,483
Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	12,500	13,582
Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	44,667	64,594
Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	14,684,599	14,346,266
Commercial, financial and agricultural
Financing Receivable, Past Due [Line Items]
Total Loans	1,406,421	1,627,477
Loans 90 Days or More Past Due and Still Accruing	0	0
Commercial, financial and agricultural | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	7,258	12,246
Commercial, financial and agricultural | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	3,070	4,576
Commercial, financial and agricultural | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,012	2,018
Commercial, financial and agricultural | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	3,176	5,652
Commercial, financial and agricultural | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	1,399,163	1,615,231
Consumer installment
Financing Receivable, Past Due [Line Items]
Total Loans	229,411	306,995
Loans 90 Days or More Past Due and Still Accruing	556	1,755
Consumer installment | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	3,471	5,621
Consumer installment | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,575	2,189
Consumer installment | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,027	1,114
Consumer installment | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	869	2,318
Consumer installment | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	225,940	301,374
Indirect automobile
Financing Receivable, Past Due [Line Items]
Total Loans	397,373	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	1,939	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	345	1,006
Indirect automobile | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	895	2,171
Indirect automobile | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	395,434	573,613
Mortgage warehouse
Financing Receivable, Past Due [Line Items]
Total Loans	841,347	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	841,347	916,353
Municipal
Financing Receivable, Past Due [Line Items]
Total Loans	647,578	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	647,578	659,403
Premium finance
Financing Receivable, Past Due [Line Items]
Total Loans	780,328	687,841
Loans 90 Days or More Past Due and Still Accruing	2,669	6,571
Premium finance | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	10,387	17,654
Premium finance | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	3,866	7,188
Premium finance | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	3,853	3,895
Premium finance | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	2,668	6,571
Premium finance | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	769,941	670,187
Real estate – construction and development
Financing Receivable, Past Due [Line Items]
Total Loans	1,527,883	1,606,710
Loans 90 Days or More Past Due and Still Accruing	1,649	0
Real estate – construction and development | Total Loans Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	22,363	19,221
Real estate – construction and development | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	18,562	13,348
Real estate – construction and development | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,037	723
Real estate – construction and development | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	2,764	5,150
Real estate – construction and development | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	1,505,520	1,587,489
Real estate – commercial and farmland
Financing Receivable, Past Due [Line Items]
Total Loans	6,051,472	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	8,190	15,722
Real estate – commercial and farmland | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	1,160	5,370
Real estate – commercial and farmland | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	618	1,701
Real estate – commercial and farmland | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	6,412	8,651
Real estate – commercial and farmland | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	6,043,282	5,284,284
Real estate – residential
Financing Receivable, Past Due [Line Items]
Total Loans	2,898,978	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	42,584	57,725
Real estate – residential | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	10,093	20,519
Real estate – residential | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	4,608	3,125
Real estate – residential | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	27,883	34,081
Real estate – residential | Current Loans
Financing Receivable, Past Due [Line Items]
Total Loans	$ 2,856,394	$ 2,738,332