Allowance for loan losses and credit quality Loan Ratings by Class (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 657,916	$ 642,461
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	494,441	496,721
Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	154,539	138,569
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	8,936	7,171
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	192,617	187,320
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	172,225	170,416
Residential Real Estate [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	17,177	14,008
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,215	2,896
Construction Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	63,245	55,322
Construction Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	43,262	41,141
Construction Real Estate [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	19,749	14,053
Construction Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	234	128
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	284,271	276,500
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	174,061	174,802
Commercial Real Estate [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	105,849	98,327
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,361	3,371
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	44,536	47,228
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	31,718	34,303
Commercial [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	11,695	12,150
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,123	775
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,566	3,241
Consumer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,494	3,209
Consumer [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	69	31
Consumer [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3	1
Municipal [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	69,681	72,850
Municipal [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	69,681	72,850
Municipal [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Municipal [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0