LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	$ 2,530,915	$ 2,469,413
Loans accounted for under the fair value option	13,726	23,321
Loans, net	2,506,984	2,452,230
Write offs after recoveries	8,800	200
Accrued interest receivable	10,800	9,800
Release of provision on pooled loans	500
Interest income on nonaccrual loans	200	0
Nonperforming Financial Instruments
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss	$ 3,800
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	41
Outstanding balance of modified loans	$ 71,300
Number of loans modified | loan	14
Loan deferral amount	$ 2,900
Consumer and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	40,754	49,391
Loans accounted for under the fair value option	$ 14,100	$ 23,400
PPP Loans | Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Percent of loans on total loan segment	3.00%	4.20%
Loans, net	$ 4,200	$ 6,900
Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	$ 139,947	$ 165,559
MSLP loan | COVID-19
Financing Receivable, Allowance for Credit Loss [Line Items]
Percent of loans on total loan segment	1.50%	1.60%
Number of loans | loan	3	5
Loans, net	$ 5,100	$ 5,900
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	337,180	$ 361,791
Number of loans, 90 days delinquent and accruing interest | loan		1
1-4 Family Residential
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	$ 927,965	$ 899,722
Number of loans, 90 days delinquent and accruing interest | loan	1
Total Loans Past Due	$ 300
Simmons Bank
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable loan	$ 208,200	$ 230,400