LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2025 USD ($) loan	Mar. 31, 2024 loan	Dec. 31, 2024 USD ($) loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 2,425,367,000		$ 2,425,565,000
Loans accounted for under the fair value option	6,112,000		7,283,000
Total, net	2,407,411,000		2,407,235,000
Interest income on nonaccrual loans	0
Accrued interest receivable	$ 9,900,000		9,800,000
Number of loans modified | loan	0
Other real estate owned, net	$ 4,385,000		35,929,000
Fair Value Carrying Amount	$ 10,000		$ 100,000
Number of loans more than 90 days delinquent | loan	0		0
Number of loans experiencing default | loan	0	0
Number of OREO loans sold | loan	2
Decrease in allowance for credit loss	$ 400,000
Significant Unobservable Inputs (Level 3)
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss on non-performing loans	45,000		$ 100,000
Consumer and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	22,941,000		24,765,000
Loans accounted for under the fair value option	6,300,000		7,500,000
Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 100,994,000		$ 119,834,000
MSLP loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Percent of loans on total loan segment			0.80%
Number of loans | loan	0		1
Total, net			$ 1,700,000
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 222,756,000		220,326,000
Loans held for sale
Financing Receivable, Allowance for Credit Loss [Line Items]
Carrying value	300,000
Simmons Bank
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 154,200,000		$ 164,300,000