composition of securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Cost of Security Sold or Transferred, Method, Specific Identification [Member]
Available-for-sale
U.S. Government Agency notes	$ 19,095	$ 7,735
Municipal bonds	27,500	25,831
U.S. Government agencies and U.S. Government - sponsored enterprises	55,435	35,240
U.S. Government agencies	14,590	17,054
Corporate bonds	8,750	8,750
Total securities available-for-sale	125,370	94,610
Non-marketable securities
Federal Home Loan Bank of Boston stock	1,713	1,713
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Available-for-sale
U.S. Government Agency notes	133	153
Municipal bonds	1,293	1,787
U.S. Government agencies and U.S. Government - sponsored enterprises	786	1,376
U.S. Government agencies	321	400
Corporate bonds	161	166
Total securities available-for-sale	2,694	3,882
Non-marketable securities
Federal Home Loan Bank of Boston stock
Accumulated Net Unrealized Investment Gain Loss 1 [Member]
Available-for-sale
U.S. Government Agency notes	86	37
Municipal bonds	74	1
U.S. Government agencies and U.S. Government - sponsored enterprises	499	43
U.S. Government agencies	62
Corporate bonds
Total securities available-for-sale	721	81
Non-marketable securities
Federal Home Loan Bank of Boston stock
Securities Financing Transaction, Fair Value [Member]
Available-for-sale
U.S. Government Agency notes	19,142	7,851
Municipal bonds	28,719	27,617
U.S. Government agencies and U.S. Government - sponsored enterprises	55,722	36,573
U.S. Government agencies	14,849	17,454
Corporate bonds	8,911	8,916
Total securities available-for-sale	127,343	98,411
CRA mutual fund	904	917
Non-marketable securities
Federal Home Loan Bank of Boston stock	$ 1,713	$ 1,713