Note 9 - Allowance for Loan Losses and Credit Quality Information - Non-accrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Non-accrual loans	$ 3,264	$ 3,144
Residential Portfolio Segment [Member]
Non-accrual loans	839	949
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member]
Non-accrual loans	35	35
Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate Other [Member]
Non-accrual loans	1,489	1,329
Consumer Portfolio Segment [Member]
Non-accrual loans	632	553
Commercial Portfolio Segment [Member]
Non-accrual loans	$ 269	$ 278