LOANS AND THE ALLOWANCE FOR LOAN LOSSES - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Loan measured at fair value	$ 20,807	$ 23,321
Total loans held for investment	2,469,038	2,469,413
Loans, net	2,449,195	2,452,230
Accrued interest receivable	$ 10,000	9,800
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	45
Outstanding balance of modified loans	$ 76,400
Number of loans modified | loan	14
Loan deferral amount	$ 3,100
Consumer and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loan measured at fair value	21,100	23,400
Total loans held for investment	$ 42,503	$ 49,391
PPP Loans | Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Percent of loans on total loan segment	3.80%	4.20%
Total loans held for investment	$ 6,000	$ 6,900
MSLP loan | COVID-19
Financing Receivable, Allowance for Credit Loss [Line Items]
Percent of loans on total loan segment	1.60%	1.60%
Number of loans | loan	4	5
Loans, net	$ 5,400	$ 5,900
Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Total loans held for investment	157,264	165,559
Loans past due over 89 days still accruing	$ 1,700
Number of loans, 90 days delinquent and accruing interest | loan	2
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Total loans held for investment	$ 341,424	$ 361,791
Loans past due over 89 days still accruing	$ 3,000
Number of loans, 90 days delinquent and accruing interest | loan	1	1
Simmons Bank
Financing Receivable, Allowance for Credit Loss [Line Items]
Total loans held for investment	$ 228,800	$ 230,400