LOANS AND THE ALLOWANCE FOR LOAN LOSSES - Summary of unpaid principal balance of loans classified as TDRs (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) loan	Mar. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Recorded Investment	$ 4,058,000	$ 4,021,000
Allowance for loan associated with TDR	(1,621,000)	(1,755,000)
Net recorded investment	1,958,000	1,787,000
Additional funds to loans classified as TDRs	$ 0	0
Number of contracts modified | loan	1
Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Recorded Investment	$ 50,000	23,000
Allowance for loan associated with TDR	(2,000)	(4,000)
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Recorded Investment	3,529,000	3,519,000
Allowance for loan associated with TDR	(1,619,000)	(1,751,000)
Loans on nonaccrual status
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans classified as TDRs		3,538,000
Total Recorded Investment	3,577,000
Loans on nonaccrual status | Cash, Securities and Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Recorded Investment	48,000	19,000
Loans on nonaccrual status | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Recorded Investment	$ 3,529,000	$ 3,519,000