LOANS AND ALLOWANCE FOR LOAN LOSSES - Loans Receivable, Excluding Purchased Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 14,480,925	$ 12,818,476	$ 8,511,914
Nonaccrual loans	76,457	75,124
Financing receivable, nonaccrual, no allowance	13,494
Balance	123,082
Allowance for Credit Losses	24,656
Commercial, financial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,627,477	802,171	680,720
Nonaccrual loans	9,836	9,236
Financing receivable, nonaccrual, no allowance	764
Balance	5,490
Allowance for Credit Losses	2,252
Consumer installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	306,995	498,577	482,559
Nonaccrual loans	709	831
Indirect automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	580,083	1,061,824	0
Nonaccrual loans	2,831	1,746
Mortgage warehouse
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	916,353	526,369	360,922
Municipal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	659,403	564,304	597,945
Premium finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	687,841	654,669	410,381
Nonaccrual loans	0	600
Balance	3,523
Allowance for Credit Losses	0
Real estate – construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,606,710	1,549,062	899,097
Nonaccrual loans	5,407	1,988
Financing receivable, nonaccrual, no allowance	416
Balance	4,173
Allowance for Credit Losses	512
Real estate – commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	5,300,006	4,353,039	3,152,388
Nonaccrual loans	18,517	23,797
Financing receivable, nonaccrual, no allowance	7,015
Balance	100,180
Allowance for Credit Losses	21,001
Real estate – residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	2,796,057	2,808,461	$ 1,927,902
Nonaccrual loans	39,157	$ 36,926
Financing receivable, nonaccrual, no allowance	5,299
Balance	9,716
Allowance for Credit Losses	$ 891