LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details)	12 Months Ended
	Dec. 31, 2024 USD ($) loan	Dec. 31, 2023 USD ($) loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	$ 2,425,565,000	$ 2,530,915,000
Loans, net	$ 2,407,235,000	$ 2,506,984,000
Number of loans, 90 days delinquent and accruing interest | loan	0
Number of loans experiencing default | loan	0	0
Interest income on nonaccrual loans	$ 0	$ 200,000
OREO carrying amount	37,000,000
OREO provision amount	1,100,000
Other real estate owned, gross	35,900,000
Other real estate owned, net	35,929,000	0
Other real estate owned, operating expense	$ 200,000	$ 0
Loans secured by real estate | loan	0	0
Accrued interest receivable	$ 9,800,000	$ 10,800,000
Decrease in allowance for credit loss	$ 5,600,000
COVID-19
Financing Receivable, Allowance for Credit Loss [Line Items]
Delinquent over period (in days)	30 days
Payments period (in years)	2 years
Number of loans modified | loan	36	41
Outstanding balance of modified loans	$ 56,400,000	$ 71,300,000
Number of loans modified | loan	11	14
Loan deferral amount	$ 2,500,000	$ 2,900,000
MSLP loan | COVID-19
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, net	$ 1,700,000	$ 5,100,000
Percent of loans on total loan segment	0.80%	1.50%
Number of loans | loan	1	3
1-4 Family Residential
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	$ 962,901,000	$ 927,965,000
Total Loans Past Due		$ 300,000
Number of loans, 90 days delinquent and accruing interest | loan		1
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	220,326,000	$ 337,180,000
Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	119,834,000	139,947,000
Cash, Securities, and Other | PPP Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, net	$ 2,000,000	$ 4,200,000
Percent of loans on total loan segment	1.70%	3.00%
Simmons Bank
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	$ 164,300,000	$ 208,200,000