composition of securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Cost of Security Sold or Transferred, Method, Specific Identification [Member]
Available-for-sale
U.S. Government Agency notes		$ 4,520
Municipal bonds		26,562
U.S. Government agencies and U.S. Government sponsored enterprises		28,961
U.S. Government agencies		25,041
Corporate bonds		5,000
Total securities available-for-sale		90,084
Non-marketable securities
Federal Home Loan Bank of Boston stock		3,242
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Available-for-sale
U.S. Government Agency notes		125
Municipal bonds		704
U.S. Government agencies and U.S. Government sponsored enterprises		420
U.S. Government agencies		468
Corporate bonds		108
Total securities available-for-sale		1,825
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		1
Municipal bonds		73
U.S. Government agencies and U.S. Government sponsored enterprises		24
U.S. Government agencies		10
Corporate bonds
Total securities available-for-sale		108
Non-marketable securities
Federal Home Loan Bank of Boston stock
Securities Financing Transaction, Fair Value [Member]
Available-for-sale
U.S. Government Agency notes		4,644
Municipal bonds		27,193
U.S. Government agencies and U.S. Government sponsored enterprises		29,357
U.S. Government agencies		25,499
Corporate bonds		5,108
Total securities available-for-sale		91,801
CRA mutual fund		882
Non-marketable securities
Federal Home Loan Bank of Boston stock		$ 3,242
Debt Securities, Available-for-sale, Cost of Security Sold or Transferred, Method, Specific Identification [Member]
Available-for-sale
U.S. Government Agency notes	$ 7,735
Municipal bonds	25,831
U.S. Government agencies and U.S. Government sponsored enterprises	35,240
U.S. Government agencies	17,054
Corporate bonds	8,750
Total securities available-for-sale	94,610
Non-marketable securities
Federal Home Loan Bank of Boston stock	1,713
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Available-for-sale
U.S. Government Agency notes	153
Municipal bonds	1,787
U.S. Government agencies and U.S. Government sponsored enterprises	1,376
U.S. Government agencies	400
Corporate bonds	166
Total securities available-for-sale	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	37
Municipal bonds	1
U.S. Government agencies and U.S. Government sponsored enterprises	43
U.S. Government agencies
Corporate bonds
Total securities available-for-sale	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	7,851
Municipal bonds	27,617
U.S. Government agencies and U.S. Government sponsored enterprises	36,573
U.S. Government agencies	17,454
Corporate bonds	8,916
Total securities available-for-sale	98,411
CRA mutual fund	917
Non-marketable securities
Federal Home Loan Bank of Boston stock	$ 1,713