Allowance for Loan Losses and Credit Quality Allowance for Loan Losses, by Class of Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	$ 6,122	$ 5,739
Provision (credit) for loan losses	2,200	775
Recoveries of amounts charged off	29	10
Balance, before amounts charged off	8,351	6,524
Amounts charged off	(80)	(402)
Balance, end of year	8,271	6,122
Residential loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	1,392	1,368
Provision (credit) for loan losses	376	150
Recoveries of amounts charged off	28	5
Balance, before amounts charged off	1,796	1,523
Amounts charged off	(20)	(131)
Balance, end of year	1,776	1,392
Construction real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	774	617
Provision (credit) for loan losses	(11)	157
Recoveries of amounts charged off	0	0
Balance, before amounts charged off	763	774
Amounts charged off	0	0
Balance, end of year	763	774
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	3,178	2,933
Provision (credit) for loan losses	1,075	305
Recoveries of amounts charged off	0	0
Balance, before amounts charged off	4,253	3,238
Amounts charged off	(54)	(60)
Balance, end of year	4,199	3,178
Commercial loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	394	354
Provision (credit) for loan losses	64	239
Recoveries of amounts charged off	0	1
Balance, before amounts charged off	458	594
Amounts charged off	0	(200)
Balance, end of year	458	394
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	23	23
Provision (credit) for loan losses	(3)	7
Recoveries of amounts charged off	1	4
Balance, before amounts charged off	21	34
Amounts charged off	(6)	(11)
Balance, end of year	15	23
Municipal
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	76	82
Provision (credit) for loan losses	138	(6)
Recoveries of amounts charged off	0	0
Balance, before amounts charged off	214	76
Amounts charged off	0	0
Balance, end of year	214	76
Unallocated
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of year	285	362
Provision (credit) for loan losses	561	(77)
Recoveries of amounts charged off	0	0
Balance, before amounts charged off	846	285
Amounts charged off	0	0
Balance, end of year	$ 846	$ 285