Carrying values and estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Carrying Reported Amount Fair Value Disclosure S A L [Member]
Financial Assets
Cash and cash equivalents	$ 175,335	$ 93,162
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale	202,396	98,411
CRA mutual fund	901	917
Federal Home Loan Bank of Boston stock	1,397	1,713
Loans held-for-sale	2,684	2,735
Loans receivable, net	1,066,750	1,027,738
Accrued interest receivable	6,260	6,373
Cash surrender value of life insurance policies	27,738	21,182
Derivative financial instruments	18	4
Financial Liabilities
Demand (non-interest-bearing)	416,073	310,769
Demand (interest-bearing)	233,600	218,869
Money market	330,436	278,146
Savings and other	237,075	189,776
Certificates of deposit	119,009	131,514
Deposits	1,336,193	1,129,074
Repurchase agreements	11,430	7,116
FHLBB advances	7,656	12,639
Subordinated debt	24,474	9,883
Note payable	170	208
Finance lease liability	4,107	1,673
Accrued interest payable	49	43
Estimate Of Fair Value Fair Value Disclosure S A L [Member]
Financial Assets
Cash and cash equivalents	175,335	93,162
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale	202,396	98,411
CRA mutual fund	901	917
Federal Home Loan Bank of Boston stock	1,397	1,713
Loans held-for-sale	2,721	2,790
Loans receivable, net	1,066,733	1,057,606
Accrued interest receivable	6,260	6,373
Cash surrender value of life insurance policies	27,738	21,182
Derivative financial instruments	18	4
Financial Liabilities
Demand (non-interest-bearing)	416,073	310,769
Demand (interest-bearing)	233,600	218,869
Money market	330,436	278,146
Savings and other	237,075	189,776
Certificates of deposit	119,716	132,875
Deposits	1,336,900	1,130,435
Repurchase agreements	11,430	7,116
FHLBB advances	7,714	12,786
Subordinated debt	24,409	10,027
Note payable	171	212
Finance lease liability	4,223	1,920
Accrued interest payable	49	43
Fair Value Inputs Level 1 S A L [Member]
Financial Assets
Cash and cash equivalents	175,335	93,162
Interest bearing time deposits with financial institutions	750	750
Securities available-for-sale
CRA mutual fund	901	917
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	202,396	98,411
CRA mutual fund
Federal Home Loan Bank of Boston stock	1,397	1,713
Loans held-for-sale
Loans receivable, net
Accrued interest receivable	6,260	6,373
Cash surrender value of life insurance policies	27,738	21,182
Derivative financial instruments	18	4
Financial Liabilities
Demand (non-interest-bearing)	416,073	310,769
Demand (interest-bearing)	233,600	218,869
Money market	330,436	278,146
Savings and other	237,075	189,776
Certificates of deposit	119,716	132,875
Deposits	1,336,900	1,130,435
Repurchase agreements	11,430	7,116
FHLBB advances	7,714	12,786
Subordinated debt	24,409	10,027
Note payable	171	212
Finance lease liability
Accrued interest payable	49	43
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	2,721	2,790
Loans receivable, net	1,066,733	1,057,606
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	4,223	1,920
Accrued interest payable