Allowance for loan losses and credit quality New Troubled Debt Restructured Loans (Details) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017 USD ($) loans	Sep. 30, 2016 USD ($) loans	Sep. 30, 2017 USD ($) loans	Sep. 30, 2016 USD ($) loans
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
New TDRs, Number of Loans \| loans	3	3	9	6
New TDRs, Pre-Modification Outstanding Recorded Investment	$ 269	$ 89	$ 649	$ 278
New TDRs, Post-Modification Outstanding Recorded Investment	$ 276	$ 99	$ 673	$ 295
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
New TDRs, Number of Loans \| loans	1	4	2	6
New TDRs, Pre-Modification Outstanding Recorded Investment	$ 149	$ 643	$ 293	$ 803
New TDRs, Post-Modification Outstanding Recorded Investment	$ 149	$ 647	$ 293	$ 807

Number of financing receivables that have been modified by troubled debt restructurings during the reporting period.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Post-modification amount of investment in financing receivables 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=66008989&loc=SL6953676-111524

+ Details

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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

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