Note 5 - Allowances for Loan Losses (Details Textual)	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Impaired Financing Receivable, Average Recorded Investment	$ 25,387,000	$ 25,695,000	$ 29,535,000
Impaired Financing Receivable, Interest Income, Accrual Method	607,000	502,000	516,000
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	590,000	$ 1,000,000	$ 765,000
Financing Receivable, Modifications, Number of Contracts		0
Financing Receivable, Modifications, Recorded Investment	8,218,000	$ 6,246,000
Financing Receivable, Modifications, Increase in Principal Balance	$ 421,000
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0	0
Mortgage Loans in Process of Foreclosure, Amount	$ 0	$ 0
Real Estate Acquired Through Foreclosure	6,966,000	10,174,000
Commercial Portfolio Segment [Member]
Impaired Financing Receivable, Average Recorded Investment	$ 4,787,000	5,185,000	$ 5,812,000
Financing Receivable, Modifications, Number of Contracts	1
Financing Receivable, Modifications, Recorded Investment	$ 1,524,000	577,000
Commercial Portfolio Segment [Member] \| Converted From Line of Credit to Term Loan With Five Year Maturity [Member]
Financing Receivable, Modifications, Recorded Investment	975,000
Owner Occupied Real Estate [Member]
Impaired Financing Receivable, Average Recorded Investment	$ 3,284,000	2,746,000	4,343,000
Financing Receivable, Modifications, Number of Contracts	1
Financing Receivable, Modifications, Recorded Investment	$ 242,000
Commercial Real Estate Portfolio Segment [Member]
Impaired Financing Receivable, Average Recorded Investment	16,069,000	16,488,000	18,340,000
Financing Receivable, Modifications, Recorded Investment	6,452,000	5,669,000
Commercial Real Estate Portfolio Segment [Member] \| Increase in Principal Blance and Reduction in Interest Rate [Member]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	6,500,000
Residential Portfolio Segment [Member]
Impaired Financing Receivable, Average Recorded Investment	26,000	26,000
Financing Receivable, Modifications, Recorded Investment
Real Estate Acquired Through Foreclosure	$ 42,000	$ 126,000

Amount of investment in financing receivables increased in related to the modification.

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
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Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

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

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Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

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Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

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Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

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