Note 9 - Allowance for Loan Losses and Credit Quality Information - Aging of Past Due Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Loans past due	$ 2,384	$ 2,990
Current loans	598,154	591,808
Loans receivable	600,538	594,798
Loans 90 days or more past due and still accruing	0	0
Residential Portfolio Segment [Member]
Loans past due	1,209	1,690
Current loans	105,846	105,315
Loans receivable	107,055	107,005
Loans 90 days or more past due and still accruing	0	0
Commercial Real Estate Portfolio Segment [Member]
Loans receivable	343,831	334,117
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member]
Loans past due	0	0
Current loans	188,450	175,177
Loans receivable	188,450	175,177
Loans 90 days or more past due and still accruing	0	0
Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate Other [Member]
Loans past due	22	0
Current loans	155,359	158,940
Loans receivable	155,381	158,940
Loans 90 days or more past due and still accruing	0	0
Consumer Portfolio Segment [Member]
Loans past due	796	1,086
Current loans	71,974	72,681
Loans receivable	72,770	73,767
Loans 90 days or more past due and still accruing	0	0
Commercial Portfolio Segment [Member]
Loans past due	357	214
Current loans	76,525	79,695
Loans receivable	76,882	79,909
Loans 90 days or more past due and still accruing	0	0
Financing Receivables, 30 to 59 Days Past Due [Member]
Loans past due	1,286	1,495
Financing Receivables, 30 to 59 Days Past Due [Member] | Residential Portfolio Segment [Member]
Loans past due	685	727
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member]
Loans past due	0	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate Other [Member]
Loans past due	0	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Loans past due	359	734
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Loans past due	242	34
Financing Receivables, 60 to 89 Days Past Due [Member]
Loans past due	88	411
Financing Receivables, 60 to 89 Days Past Due [Member] | Residential Portfolio Segment [Member]
Loans past due	0	294
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member]
Loans past due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate Other [Member]
Loans past due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Loans past due	88	117
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Loans past due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans past due	1,010	1,084
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Residential Portfolio Segment [Member]
Loans past due	524	669
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member]
Loans past due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate Other [Member]
Loans past due	22	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Loans past due	349	235
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Loans past due	$ 115	$ 180