LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details)	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2025 USD ($) loan	Jun. 30, 2025 loan	Sep. 30, 2025 USD ($) loan	Sep. 30, 2024 loan	Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans (includes $4,208 and $7,283 measured at fair value, respectively)	$ 2,590,846,000		$ 2,590,846,000			$ 2,425,565,000
Loans accounted for under the fair value option	4,208,000		4,208,000			7,283,000
Total, net	2,569,879,000		2,569,879,000			2,407,235,000
Accrued interest receivable	$ 11,100,000		11,100,000			9,800,000
Number of loans modified | loan	0
Other real estate owned, net	$ 4,389,000		4,389,000			35,929,000
Fair Value Carrying Amount	$ 100,000		$ 100,000			100,000
Number of loans more than 90 days delinquent | loan	2		2
90 days or more past due, still accruing						0
Number of loans experiencing default | loan			0	0
Number of OREO loans sold | loan			2
Significant Unobservable Inputs (Level 3)
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss on non-performing loans	$ 3,900,000		$ 3,900,000			100,000
Consumer and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans (includes $4,208 and $7,283 measured at fair value, respectively)	16,557,000		16,557,000			24,765,000
Loans accounted for under the fair value option	4,300,000		4,300,000			7,500,000
Cash, Securities, and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans (includes $4,208 and $7,283 measured at fair value, respectively)	159,182,000		$ 159,182,000			$ 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		1	0
Total, net						$ 1,700,000
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans (includes $4,208 and $7,283 measured at fair value, respectively)	225,119,000		$ 225,119,000			220,326,000
Loans held for sale
Financing Receivable, Allowance for Credit Loss [Line Items]
Carrying value					$ 300,000
Owner Occupied CRE
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans (includes $4,208 and $7,283 measured at fair value, respectively)	190,290,000		190,290,000			172,019,000
90 days or more past due, still accruing	1,000,000		1,000,000
Simmons Bank
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans (includes $4,208 and $7,283 measured at fair value, respectively)	$ 124,100,000		$ 124,100,000			$ 164,300,000