FAIR VALUE OF ASSETS AND LIABILITIES - Carrying value and estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Carrying value
Financial Assets
Cash and cash equivalents	$ 84,495	$ 26,885
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale, net	89,452	91,801
CRA mutual fund	912	882
Federal Home Loan Bank of Boston stock	3,353	3,242
Loans held-for-sale	5,313	332
Loans receivable, net	1,040,358	927,413
Accrued interest receivable	3,988	3,415
Cash surrender value of life insurance policies	20,846	20,580
Financial Liabilities
Demand (non-interest-bearing)	325,531	237,852
Demand (interest-bearing)	188,487	153,314
Money market	251,242	239,504
Savings and other	170,537	161,112
Certificates of deposit	149,802	127,724
Deposits	1,085,599	919,506
Repurchase agreements	7,809	8,530
FHLBB advances	55,118	50,887
Subordinated debt	9,871	9,859
Note payable	228	246
Finance lease liability	1,696	1,718
Accrued interest payable	187	78
Estimated fair value
Financial Assets
Cash and cash equivalents	84,495	26,885
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale, net	89,452	91,801
CRA mutual fund	912	882
Federal Home Loan Bank of Boston stock	3,353	3,242
Loans held-for-sale	5,392	334
Loans receivable, net	1,062,289	933,287
Accrued interest receivable	3,988	3,415
Cash surrender value of life insurance policies	20,846	20,580
Financial Liabilities
Demand (non-interest-bearing)	325,531	237,852
Demand (interest-bearing)	188,487	153,314
Money market	251,242	239,504
Savings and other	170,537	161,112
Certificates of deposit	151,315	128,629
Deposits	1,087,112	920,411
Repurchase agreements	7,809	8,530
FHLBB advances	55,377	51,028
Subordinated debt	9,910	10,113
Note payable	231	251
Finance lease liability	1,902	1,967
Accrued interest payable	187	78
Fair Value Measurements Using - Level 1
Financial Assets
Cash and cash equivalents	84,495	26,885
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale, net
CRA mutual fund	912	882
Federal Home Loan Bank of Boston stock	3,353	3,242
Loans held-for-sale
Loans receivable, net
Accrued interest receivable	3,988	3,415
Cash surrender value of life insurance policies	20,846	20,580
Financial Liabilities
Demand (non-interest-bearing)
Demand (interest-bearing)
Money market
Savings and other
Certificates of deposit
Deposits
Repurchase agreements
FHLBB advances
Subordinated debt	9,910	10,113
Note payable
Finance lease liability
Accrued interest payable	187	78
Fair Value Measurements Using - Level 2
Financial Assets
Cash and cash equivalents
Interest bearing time deposits with financial institutions
Securities available-for-sale, net	89,452	91,801
CRA mutual fund
Federal Home Loan Bank of Boston stock
Loans held-for-sale
Loans receivable, net
Accrued interest receivable
Cash surrender value of life insurance policies
Financial Liabilities
Demand (non-interest-bearing)	325,531	237,852
Demand (interest-bearing)	188,487	153,314
Money market	251,242	239,504
Savings and other	170,537	161,112
Certificates of deposit	151,315	128,629
Deposits	1,087,112	920,411
Repurchase agreements	7,809	8,530
FHLBB advances	55,377	51,028
Subordinated debt
Note payable	231	251
Finance lease liability
Accrued interest payable
Fair Value Measurements Using - Level 3
Financial Assets
Cash and cash equivalents
Interest bearing time deposits with financial institutions
Securities available-for-sale, net
CRA mutual fund
Federal Home Loan Bank of Boston stock
Loans held-for-sale	5,392	334
Loans receivable, net	1,062,289	933,287
Accrued interest receivable
Cash surrender value of life insurance policies
Financial Liabilities
Demand (non-interest-bearing)
Demand (interest-bearing)
Money market
Savings and other
Certificates of deposit
Deposits
Repurchase agreements
FHLBB advances
Subordinated debt
Note payable
Finance lease liability	1,902	1,967
Accrued interest payable