LOANS AND ALLOWANCE FOR LOAN LOSSES - Analysis of Past-Due Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	$ 134,659	$ 184,006
Financing receivable, not past due	14,346,266	12,634,470
Loans, net of unearned income	14,480,925	12,818,476	$ 8,511,914
Loans 90 Days or More Past Due and Still Accruing	8,326	5,754
Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	56,483	88,291
Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	13,582	32,582
Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	64,594	63,133
Commercial, financial and agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	12,246	12,344
Financing receivable, not past due	1,615,231	789,827
Loans, net of unearned income	1,627,477	802,171	680,720
Loans 90 Days or More Past Due and Still Accruing	0	0
Commercial, financial and agricultural | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	4,576	3,609
Commercial, financial and agricultural | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	2,018	2,251
Commercial, financial and agricultural | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	5,652	6,484
Consumer installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	5,621	6,276
Financing receivable, not past due	301,374	492,301
Loans, net of unearned income	306,995	498,577	482,559
Loans 90 Days or More Past Due and Still Accruing	1,755	922
Consumer installment | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	2,189	3,488
Consumer installment | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	1,114	1,336
Consumer installment | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	2,318	1,452
Indirect automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	6,470	8,567
Financing receivable, not past due	573,613	1,053,257
Loans, net of unearned income	580,083	1,061,824	0
Loans 90 Days or More Past Due and Still Accruing	0	21
Indirect automobile | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	3,293	5,978
Indirect automobile | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	1,006	1,067
Indirect automobile | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	2,171	1,522
Mortgage warehouse
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	0	0
Financing receivable, not past due	916,353	526,369
Loans, net of unearned income	916,353	526,369	360,922
Loans 90 Days or More Past Due and Still Accruing	0	0
Mortgage warehouse | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	0	0
Mortgage warehouse | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	0	0
Mortgage warehouse | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	0	0
Municipal
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	0	0
Financing receivable, not past due	659,403	564,304
Loans, net of unearned income	659,403	564,304	597,945
Loans 90 Days or More Past Due and Still Accruing	0	0
Municipal | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	0	0
Municipal | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	0	0
Municipal | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	0	0
Premium finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	17,654	27,234
Financing receivable, not past due	670,187	627,435
Loans, net of unearned income	687,841	654,669	410,381
Loans 90 Days or More Past Due and Still Accruing	6,571	4,811
Premium finance | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	7,188	13,801
Premium finance | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	3,895	8,022
Premium finance | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	6,571	5,411
Real estate – construction and development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	19,221	10,592
Financing receivable, not past due	1,587,489	1,538,470
Loans, net of unearned income	1,606,710	1,549,062	899,097
Loans 90 Days or More Past Due and Still Accruing	0	0
Real estate – construction and development | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	13,348	7,785
Real estate – construction and development | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	723	1,224
Real estate – construction and development | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	5,150	1,583
Real estate – commercial and farmland
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	15,722	26,407
Financing receivable, not past due	5,284,284	4,326,632
Loans, net of unearned income	5,300,006	4,353,039	3,152,388
Loans 90 Days or More Past Due and Still Accruing	0	0
Real estate – commercial and farmland | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	5,370	7,404
Real estate – commercial and farmland | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	1,701	3,405
Real estate – commercial and farmland | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	8,651	15,598
Real estate – residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	57,725	92,586
Financing receivable, not past due	2,738,332	2,715,875
Loans, net of unearned income	2,796,057	2,808,461	$ 1,927,902
Loans 90 Days or More Past Due and Still Accruing	0	0
Real estate – residential | Loans 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	20,519	46,226
Real estate – residential | Loans 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	3,125	15,277
Real estate – residential | Loans 90 or More Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable, past due	$ 34,081	$ 31,083