LOANS AND ALLOWANCE FOR CREDIT LOSSES - Loans Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 14,824,539	$ 14,480,925
Commercial, financial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,217,575	1,627,477
Consumer installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	207,111	306,995
Indirect automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	325,057	580,083
Mortgage warehouse
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	768,577	916,353
Municipal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	624,430	659,403
Premium finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	840,737	687,841
Real estate – construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	1,454,824	1,606,710
Real estate – commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	6,409,704	5,300,006
Real estate – residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 2,976,524	$ 2,796,057