LOANS AND THE ALLOWANCE FOR LOAN LOSSES - Summary of loans (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) loan	May 15, 2020 USD ($)	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 1,507,484		$ 996,559
Deferred costs, net	(1,408)		1,448
Allowance for loan losses	(11,845)		(7,875)
Net loans	1,494,231		990,132
Loans, net	1,494,231		990,132
Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	124,700	$ 120,642
Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	371,481		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	105,717		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	446,959		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	243,564		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	154,138		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	185,625		$ 128,457
Commercial and Industrial | Simmons Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		$ 58,660
Paycheck Protection Program Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	206,100
Paycheck Protection Program Loan [Member] | Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 206,100
Percent of Loans on Total Loan Segment	55.50%
COVID-19 [Member] | MSLP loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net loans	$ 2,400
Loans, net	$ 2,400
Number of loans | loan	1