Note 10 - Fair Value Measurement - Quantitative Information About Level 3 Fair Value Measurements for Financial Instruments Measured at Fair Value on a Non-recurring Basis (Details) $ in Thousands	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commercial Portfolio Segment [Member] | Real Estate Loan [Member] | Measurement Input, Cost to Sell [Member]
Impaired loans, Measurement Input	0.1
Commercial Portfolio Segment [Member] | Real Estate Loan [Member] | Measurement Input, Cost to Sell [Member] | Weighted Average [Member]
Impaired loans, Measurement Input	0.1
Other real estate, Measurement Input	0.16	0.16
Commercial Portfolio Segment [Member] | Real Estate Loan [Member] | Measurement Input, Cost to Sell [Member] | Minimum [Member]
Other real estate, Measurement Input	0.16	0.16
Commercial Portfolio Segment [Member] | Real Estate Loan [Member] | Measurement Input, Cost to Sell [Member] | Maximum [Member]
Other real estate, Measurement Input	0.17	0.17
Commercial Portfolio Segment [Member] | Construction Loans [Member] | Measurement Input, Cost to Sell [Member] | Weighted Average [Member]
Other real estate, Measurement Input	0.24	0.24
Commercial Portfolio Segment [Member] | Construction Loans [Member] | Measurement Input, Cost to Sell [Member] | Minimum [Member]
Other real estate, Measurement Input	0.1	0.1
Commercial Portfolio Segment [Member] | Construction Loans [Member] | Measurement Input, Cost to Sell [Member] | Maximum [Member]
Other real estate, Measurement Input	0.51	0.51
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Measurement Input, Cost to Sell [Member] | Weighted Average [Member]
Other real estate, Measurement Input	0.16	0.16
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Measurement Input, Cost to Sell [Member] | Minimum [Member]
Other real estate, Measurement Input	0.1	0.1
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Measurement Input, Cost to Sell [Member] | Maximum [Member]
Other real estate, Measurement Input	0.34	0.34
Fair Value, Nonrecurring [Member]
Other real estate	$ 1,170	$ 1,170
Fair Value, Nonrecurring [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Impaired loans	418
Other real estate	347	347
Fair Value, Nonrecurring [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Impaired loans	418
Other real estate	455	455
Fair Value, Nonrecurring [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Other real estate	$ 368	$ 368