Allowance for loan losses and credit quality Allocation of Investment in Loans, by Impairment Methodology (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 3,900	$ 5,296
Collectively evaluated for impairment	575,002	527,994
Loans	578,902	533,290
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,939	1,448
Collectively evaluated for impairment	174,460	171,279
Loans	176,399	172,727
Construction Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	84	88
Collectively evaluated for impairment	36,712	34,101
Loans	36,796	34,189
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,484	3,328
Collectively evaluated for impairment	255,708	245,735
Loans	257,192	249,063
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	393	432
Collectively evaluated for impairment	47,773	41,567
Loans	48,166	41,999
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	3,832	3,962
Loans	3,832	3,962
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	56,517	31,350
Loans	$ 56,517	$ 31,350

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.

No definition available.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

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- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

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- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

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