Carrying values and estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Carrying Reported Amount Fair Value Disclosure S A L [Member]
Financial Assets
Cash and cash equivalents	$ 71,467	$ 175,335
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale	203,110	202,396
Mutual funds	1,672	901
Federal Home Loan Bank of Boston stock	945	1,397
Loans held-for-sale		2,684
Loans receivable, net	1,135,758	1,066,750
Accrued interest receivable	6,123	6,260
Cash surrender value of life insurance policies	28,063	27,738
Derivative financial instruments	49	18
Financial Liabilities
Demand (non-interest-bearing)	383,674	416,073
Demand (interest-bearing)	233,947	233,600
Money market	314,244	330,436
Savings and other	231,322	237,075
Certificates of deposit	153,352	119,009
Deposits	1,316,539	1,336,193
Repurchase agreements	16,574	11,430
FHLBB advances		7,656
Subordinated debt	24,502	24,474
Note payable	149	170
Finance lease liability	4,329	4,107
Accrued interest payable	44	49
Estimate Of Fair Value Fair Value Disclosure S A L [Member]
Financial Assets
Cash and cash equivalents	71,467	175,335
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale	203,110	202,396
Mutual funds	1,672	901
Federal Home Loan Bank of Boston stock	945	1,397
Loans held-for-sale		2,721
Loans receivable, net	1,112,258	1,066,733
Accrued interest receivable	6,123	6,260
Cash surrender value of life insurance policies	28,063	27,738
Derivative financial instruments	49	18
Financial Liabilities
Demand (non-interest-bearing)	383,674	416,073
Demand (interest-bearing)	233,947	233,600
Money market	314,244	330,436
Savings and other	231,322	237,075
Certificates of deposit	153,321	119,716
Deposits	1,316,508	1,336,900
Repurchase agreements	16,574	11,430
FHLBB advances		7,714
Subordinated debt	22,428	24,409
Note payable	151	171
Finance lease liability	4,267	4,223
Accrued interest payable	44	49
Fair Value Inputs Level 1 S A L [Member]
Financial Assets
Cash and cash equivalents	71,467	175,335
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale
Mutual funds	1,672	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	203,110	202,396
Mutual funds
Federal Home Loan Bank of Boston stock	945	1,397
Loans held-for-sale
Loans receivable, net
Accrued interest receivable	6,123	6,260
Cash surrender value of life insurance policies	28,063	27,738
Derivative financial instruments	49	18
Financial Liabilities
Demand (non-interest-bearing)	383,674	416,073
Demand (interest-bearing)	233,947	233,600
Money market	314,244	330,436
Savings and other	231,322	237,075
Certificates of deposit	153,321	119,716
Deposits	1,316,508	1,336,900
Repurchase agreements	16,574	11,430
FHLBB advances		7,714
Subordinated debt	22,428	24,409
Note payable	151	171
Finance lease liability
Accrued interest payable	44	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
Mutual funds
Federal Home Loan Bank of Boston stock
Loans held-for-sale		2,721
Loans receivable, net	1,112,258	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	4,267	4,223
Accrued interest payable