Note 9 - Allowance for Loan Losses and Credit Quality Information - Trouble Debt Restructuring (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Troubled debt restructurings	$ 2,575	$ 3,044
Performing Financial Instruments [Member]
Troubled debt restructurings	771	1,129
Nonperforming Financial Instruments [Member]
Troubled debt restructurings	1,804	1,915
Residential Portfolio Segment [Member]
Troubled debt restructurings	486	685
Residential Portfolio Segment [Member] | Performing Financial Instruments [Member]
Troubled debt restructurings	333	573
Residential Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Troubled debt restructurings	153	112
Commercial Real Estate Portfolio Segment [Member]
Troubled debt restructurings	1,193	1,210
Commercial Real Estate Portfolio Segment [Member] | Performing Financial Instruments [Member]
Troubled debt restructurings	0	0
Commercial Real Estate Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Troubled debt restructurings	1,193	1,210
Consumer Portfolio Segment [Member]
Troubled debt restructurings	531	758
Consumer Portfolio Segment [Member] | Performing Financial Instruments [Member]
Troubled debt restructurings	227	327
Consumer Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Troubled debt restructurings	304	431
Commercial Portfolio Segment [Member]
Troubled debt restructurings	365	391
Commercial Portfolio Segment [Member] | Performing Financial Instruments [Member]
Troubled debt restructurings	211	229
Commercial Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Troubled debt restructurings	$ 154	$ 162