LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2023 USD ($) loan	Jun. 30, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 2,495,582	$ 2,495,582	$ 2,469,413
Loans accounted for under the fair value option	17,523	17,523	23,321
Total, net	2,473,538	2,473,538	2,452,230
Advances to customers experiencing financial difficulty	300	500
Interest income on nonaccrual loans	200	200
Accrued interest receivable	10,500	10,500	9,800
Payments Received On Financing Receivable, Nonaccrual	$ 1,800
Number of non-accrual loans paid opff | loan	2
Release of provision on pooled loans		800
Allowance increase on analyzed loans	$ 2,195	$ 2,195
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		$ 76,000
Number of loans modified | loan		14
Loan deferral amount	3,100	$ 3,100
Consumer and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	39,285	39,285	49,391
Loans accounted for under the fair value option	18,300	18,300	23,400
PPP Loans | Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 5,400	$ 5,400	$ 6,900
Percent of loans on total loan segment	3.60%	3.60%	4.20%
Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 150,620	$ 150,620	$ 165,559
MSLP loan | COVID-19
Financing Receivable, Allowance for Credit Loss [Line Items]
Percent of loans on total loan segment	1.60%	1.60%	1.60%
Number of loans | loan		4	5
Total, net	$ 5,500	$ 5,500	$ 5,900
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	339,399	339,399	$ 361,791
Number of loans, 90 days delinquent and accruing interest | loan			1
Allowance increase on analyzed loans	2,195	2,195
Simmons Bank
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 221,000	$ 221,000	$ 230,400