LOANS AND THE ALLOWANCE FOR LOAN LOSSES - Summary of loans (Details) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2022 USD ($) loan	Dec. 31, 2021 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	$ 2,354,898	$ 1,954,168
Deferred fees and unamortized premiums/(unaccreted discounts), net	(3,576)	(5,031)
Allowance for loan losses	(16,081)	(13,732)
Loans, net	2,335,241	1,935,405
Loan measured at fair value	22,871	0
Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	248,600	356,700
Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	154,748	261,190
Consumer and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	50,429	34,758
Loan measured at fair value	22,600
Construction and Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	228,060	178,716
1-4 Family Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	822,796	580,872
Non-Owner Occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	527,836	482,622
Owner Occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	220,075	212,426
Commercial. and Industrial.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	350,954	203,584
PPP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	7,700	46,800
PPP Loans \| Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	$ 7,700	$ 46,800
Percent of Loans on Total Loan Segment	5.00%	17.90%
MSLP loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	$ 6,800	$ 6,800
COVID-19 \| MSLP loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	$ 6,800	$ 6,800
Percent of Loans on Total Loan Segment	1.90%	3.30%
Number of loans \| loan	5	5

Amount of loans held for investment under the fair value option.

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Percentage of class of loan on a particular portfolio segment.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount, before allowance and fees, of loans and leases receivable. Excludes loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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