Carrying values and estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Carrying Reported Amount Fair Value Disclosure S A L [Member]
Financial Assets
Cash and cash equivalents	$ 56,297	$ 175,335
Securities available-for-sale	189,161	202,396
Mutual funds	1,882	901
Federal Home Loan Bank of Boston stock	1,487	1,397
Loans receivable, net	1,176,493	1,066,750
Accrued interest receivable	6,012	6,260
Cash surrender value of life insurance policies	30,187	27,738
Financial Liabilities
Demand (non-interest-bearing)	413,584	416,073
Demand (interest-bearing)	241,236	233,600
Money market	313,987	330,436
Savings and other	246,538	237,075
Certificates of deposit	109,859	119,009
Deposits	1,325,204	1,336,193
Repurchase agreements	7,109	11,430
FHLBB advances	20,000	7,656
Subordinated debt	24,517	24,474
Note payable	139	170
Finance lease liability	4,296	4,107
Accrued interest payable	18	49
Interest bearing time deposits with financial institutions		750
Loans held-for-sale		2,684
Derivative financial instruments		18
Estimate Of Fair Value Fair Value Disclosure S A L [Member]
Financial Assets
Cash and cash equivalents	56,297	175,335
Securities available-for-sale	189,161	202,396
Mutual funds	1,882	901
Federal Home Loan Bank of Boston stock	1,487	1,397
Loans receivable, net	1,154,834	1,066,733
Accrued interest receivable	6,012	6,260
Cash surrender value of life insurance policies	30,187	27,738
Financial Liabilities
Demand (non-interest-bearing)	413,584	416,073
Demand (interest-bearing)	241,236	233,600
Money market	313,987	330,436
Savings and other	246,538	237,075
Certificates of deposit	109,536	119,716
Deposits	1,324,881	1,336,900
Repurchase agreements	7,109	11,430
FHLBB advances	20,000	7,714
Subordinated debt	21,514	24,409
Note payable	135	171
Finance lease liability	3,916	4,223
Accrued interest payable	18	49
Interest bearing time deposits with financial institutions		750
Loans held-for-sale		2,721
Derivative financial instruments		18
Fair Value Inputs Level 1 S A L [Member]
Financial Assets
Cash and cash equivalents	56,297	175,335
Securities available-for-sale
Mutual funds	1,882	901
Federal Home Loan Bank of Boston stock
Loans receivable, net
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
Accrued interest payable
Interest bearing time deposits with financial institutions		750
Loans held-for-sale
Derivative financial instruments
Fair Value Inputs Level 2 S A L [Member]
Financial Assets
Cash and cash equivalents
Securities available-for-sale	189,161	202,396
Mutual funds
Federal Home Loan Bank of Boston stock	1,487	1,397
Loans receivable, net
Accrued interest receivable	6,012	6,260
Cash surrender value of life insurance policies	30,187	27,738
Financial Liabilities
Demand (non-interest-bearing)	413,584	416,073
Demand (interest-bearing)	241,236	233,600
Money market	313,987	330,436
Savings and other	246,538	237,075
Certificates of deposit	109,536	119,716
Deposits	1,324,881	1,336,900
Repurchase agreements	7,109	11,430
FHLBB advances	20,000	7,714
Subordinated debt	21,517	24,409
Note payable	135	171
Finance lease liability
Accrued interest payable	18	49
Interest bearing time deposits with financial institutions
Loans held-for-sale
Derivative financial instruments		18
Fair Value Inputs Level 3 S A L [Member]
Financial Assets
Cash and cash equivalents
Securities available-for-sale
Mutual funds
Federal Home Loan Bank of Boston stock
Loans receivable, net	1,154,834	1,066,733
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	3,916	4,223
Accrued interest payable
Interest bearing time deposits with financial institutions
Loans held-for-sale		2,721
Derivative financial instruments