Allowance for loan losses and credit quality Troubled Debt Restructured Loans (Details) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($) loans	Dec. 31, 2015 USD ($) loans
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans, Number of Loans \| loans	33	19
Troubled Debt Restructured Loans, Principal Balance \| $	$ 3,419	$ 2,732
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans, Number of Loans \| loans	20	11
Troubled Debt Restructured Loans, Principal Balance \| $	$ 1,448	$ 1,197
Construction Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans, Number of Loans \| loans	1	1
Troubled Debt Restructured Loans, Principal Balance \| $	$ 88	$ 92
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans, Number of Loans \| loans	10	5
Troubled Debt Restructured Loans, Principal Balance \| $	$ 1,452	$ 950
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans, Number of Loans \| loans	2	2
Troubled Debt Restructured Loans, Principal Balance \| $	$ 431	$ 493

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953676-111524

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- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

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