Carrying values and estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Carrying Reported Amount Fair Value Disclosure S A L [Member]
Financial Assets
Cash and cash equivalents	$ 98,861	$ 175,335
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale	215,652	202,396
CRA mutual fund	862	901
Federal Home Loan Bank of Boston stock	1,077	1,397
Loans held-for-sale	1,070	2,684
Loans receivable, net	1,066,216	1,066,750
Accrued interest receivable	5,895	6,260
Cash surrender value of life insurance policies	27,900	27,738
Derivative financial instruments	47	18
Financial Liabilities
Demand (non-interest-bearing)	370,082	416,073
Demand (interest-bearing)	233,893	233,600
Money market	317,462	330,436
Savings and other	240,824	237,075
Certificates of deposit	128,213	119,009
Deposits	1,290,474	1,336,193
Repurchase agreements	8,161	11,430
FHLBB advances	419	7,656
Subordinated debt	24,488	24,474
Note payable	159	170
Finance lease liability	4,363	4,107
Accrued interest payable	37	49
Estimate Of Fair Value Fair Value Disclosure S A L [Member]
Financial Assets
Cash and cash equivalents	98,861	175,335
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale	215,652	202,396
CRA mutual fund	862	901
Federal Home Loan Bank of Boston stock	1,077	1,397
Loans held-for-sale	1,077	2,721
Loans receivable, net	1,055,745	1,066,733
Accrued interest receivable	5,895	6,260
Cash surrender value of life insurance policies	27,900	27,738
Derivative financial instruments	47	18
Financial Liabilities
Demand (non-interest-bearing)	370,082	416,073
Demand (interest-bearing)	233,893	233,600
Money market	317,462	330,436
Savings and other	240,824	237,075
Certificates of deposit	128,663	119,716
Deposits	1,290,924	1,336,900
Repurchase agreements	8,161	11,430
FHLBB advances	419	7,714
Subordinated debt	24,409	24,409
Note payable	162	171
Finance lease liability	4,312	4,223
Accrued interest payable	37	49
Fair Value Inputs Level 1 S A L [Member]
Financial Assets
Cash and cash equivalents	98,861	175,335
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale
CRA mutual fund	862	901
Federal Home Loan Bank of Boston stock
Loans held-for-sale
Loans receivable, net
Accrued interest receivable
Cash surrender value of life insurance policies
Derivative financial instruments
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
Accrued interest payable
Fair Value Inputs Level 2 S A L [Member]
Financial Assets
Cash and cash equivalents
Interest bearing time deposits with financial institutions
Securities available-for-sale	215,652	202,396
CRA mutual fund
Federal Home Loan Bank of Boston stock	1,077	1,397
Loans held-for-sale
Loans receivable, net
Accrued interest receivable	5,895	6,260
Cash surrender value of life insurance policies	27,900	27,738
Derivative financial instruments	47	18
Financial Liabilities
Demand (non-interest-bearing)	370,082	416,073
Demand (interest-bearing)	233,893	233,600
Money market	317,462	330,436
Savings and other	240,824	237,075
Certificates of deposit	128,663	119,716
Deposits	1,290,924	1,336,900
Repurchase agreements	8,161	11,430
FHLBB advances	419	7,714
Subordinated debt	24,409	24,409
Note payable	162	171
Finance lease liability
Accrued interest payable	37	49
Fair Value Inputs Level 3 S A L [Member]
Financial Assets
Cash and cash equivalents
Interest bearing time deposits with financial institutions
Securities available-for-sale
CRA mutual fund
Federal Home Loan Bank of Boston stock
Loans held-for-sale	1,077	2,721
Loans receivable, net	1,055,745	1,066,733
Accrued interest receivable
Cash surrender value of life insurance policies
Derivative financial instruments
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	4,312	4,223
Accrued interest payable