ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Additional Information (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) SecurityLoan loan	Mar. 31, 2020 USD ($) loan	Dec. 31, 2020 USD ($) SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income on impaired loans	$ 200,000	$ 200,000
Loan workout and other credit costs	1,120,000	453,000
Troubled debt restructuring related reserves (less than)	$ 200,000		$ 100,000
Usual sustained repayment performance period	6 months
Increase (decrease) in allowance for loan losses (less than)	$ 100,000	100,000
Troubled debt restructurings charged off	$ 0	$ 0
TRD defaulted | loan	0	0
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of residential loans in the process of foreclosure | SecurityLoan	24		27
Total loans outstanding, residential loans	$ 1,400,000		$ 1,900,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of residential loans in the process of foreclosure | SecurityLoan	26		23
Total loans outstanding, residential loans	$ 12,600,000		$ 12,800,000
Residential and Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan workout and other credit costs	$ 500,000	$ 700,000
Impairment loans, charge off period	90 days