Allowance for loan losses and credit quality Loan Ratings by Class (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 536,200	$ 533,290
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	421,097	443,132
Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	106,635	80,807
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	8,468	9,351
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	175,322	172,727
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	161,187	158,140
Residential Real Estate [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	10,535	10,641
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,600	3,946
Construction Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	40,735	34,189
Construction Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	30,693	29,248
Construction Real Estate [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	9,893	4,830
Construction Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	149	111
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	252,354	249,063
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	166,271	182,247
Commercial Real Estate [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	82,212	62,193
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,871	4,623
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	46,598	41,999
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	41,817	38,219
Commercial [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,933	3,109
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	848	671
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,537	3,962
Consumer [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,475	3,928
Consumer [Member] | Satisfactory/Monitor [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	62	34
Consumer [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Municipal [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	17,654	31,350
Municipal [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	17,654	31,350
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