Allowance for loan losses and credit quality Loan Ratings by Class (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 533,290	$ 500,506
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	443,132	422,391
Satisfactory and Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	80,807	68,487
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	9,351	9,628
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	172,727	165,396
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	158,140	150,535
Residential Real Estate [Member] | Satisfactory and Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	10,641	11,329
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,946	3,532
Construction Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	34,189	42,889
Construction Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	29,248	37,750
Construction Real Estate [Member] | Satisfactory and Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,830	4,968
Construction Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	111	171
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	249,063	230,442
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	182,247	175,438
Commercial Real Estate [Member] | Satisfactory and Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	62,193	49,745
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,623	5,259
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	41,999	21,397
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	38,219	18,347
Commercial [Member] | Satisfactory and Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,109	2,384
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	671	666
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,962	3,963
Consumer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,928	3,902
Consumer [Member] | Satisfactory and Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	34	61
Consumer [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Municipal [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	31,350	36,419
Municipal [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	31,350	36,419
Municipal [Member] | Satisfactory and Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Municipal [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0