LOANS AND THE ALLOWANCE FOR LOAN LOSSES - Summary of loans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) loan	May 15, 2020 USD ($)	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 1,534,185		$ 996,559
Deferred costs, net	(1,352)		1,448
Allowance for loan losses	(12,539)		(7,875)
Net loans	1,520,294		990,132
Loans, net	1,520,294		990,132
Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	127,200	$ 120,642
Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	357,020		146,701
Cash, Securities and Other | Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		13,457
Construction and Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	131,111		28,120
Construction and Development | Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		40,407
1-4 Family Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	455,038		400,134
1-4 Family Residential | Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		7,252
Non-Owner Occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	281,943		165,179
Non-Owner Occupied CRE | Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		545
Owner Occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	163,042		127,968
Owner Occupied CRE | Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		321
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	146,031		$ 128,457
Commercial and Industrial | Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		58,660
PPP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	142,900
PPP Loans | Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		$ 12,900
PPP Loans | Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 142,900
Percent of Loans on Total Loan Segment	40.00%
MSLP loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 6,600
Percent of Loans on Total Loan Segment	4.50%
COVID-19
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 1,534,185
COVID-19 | Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	357,020
COVID-19 | Construction and Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	131,111
COVID-19 | 1-4 Family Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	455,038
COVID-19 | Non-Owner Occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	281,943
COVID-19 | Owner Occupied CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	163,042
COVID-19 | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	146,031
COVID-19 | MSLP loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net loans	6,600
Loans, net	$ 6,600
Number of loans | loan	6