Note 10 - Fair Value of Financial Instruments - Quantitative Information About Non-recurring Level 3 Fair Value of Financial Instruments and the Fair Value Measurements (Details) $ in Thousands	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Measurements, Nonrecurring [Member]
Impaired loans	$ 12,798	$ 16,027
Other Repossessed Assets	$ 35
Valuation, Income Approach [Member] | Measurement Input, Cap Rate [Member] | Minimum [Member]
Impaired loans, Measurement Input	0.065	0.065
Valuation, Income Approach [Member] | Measurement Input, Cap Rate [Member] | Maximum [Member]
Impaired loans, Measurement Input	0.075	0.075
Valuation, Income Approach [Member] | Measurement Input, Cap Rate [Member] | Weighted Average [Member]
Impaired loans, Measurement Input	0.07	0.068
Valuation, Income Approach [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	0.15	0.15
Valuation, Income Approach [Member] | Measurement Input, Loss Severity [Member] | Weighted Average [Member]
Impaired loans, Measurement Input	0.15	0.15
Valuation, Income Approach [Member] | Fair Value, Measurements, Nonrecurring [Member] | Measurement Input, Cap Rate [Member]
Impaired loans	$ 1,525	$ 1,818
Valuation, Market Approach [Member] | Measurement Input, Loss Severity [Member]
Other repossesed assets, Measurement Input	0.15
Valuation, Market Approach [Member] | Measurement Input, Loss Severity [Member] | Minimum [Member]
Impaired loans, Measurement Input	(0.386)	(0.309)
Valuation, Market Approach [Member] | Measurement Input, Loss Severity [Member] | Maximum [Member]
Impaired loans, Measurement Input	0.15	0.15
Valuation, Market Approach [Member] | Measurement Input, Loss Severity [Member] | Weighted Average [Member]
Impaired loans, Measurement Input	0.111	0.087
Other repossesed assets, Measurement Input	0.15
Valuation, Market Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Minimum [Member]
Impaired loans, Measurement Input	(0.5)	(0.5)
Valuation, Market Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Maximum [Member]
Impaired loans, Measurement Input	0.15	0.162
Valuation, Market Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Weighted Average [Member]
Impaired loans, Measurement Input	0.021	0.008
Valuation, Market Approach [Member] | Fair Value, Measurements, Nonrecurring [Member]
Impaired loans	$ 8,358	$ 10,003
Other Repossessed Assets	$ 35
Blended Income and Sales Approach [Member] | Measurement Input, Cap Rate [Member] | Minimum [Member]
Impaired loans, Measurement Input	0.05	0.05
Blended Income and Sales Approach [Member] | Measurement Input, Cap Rate [Member] | Maximum [Member]
Impaired loans, Measurement Input	0.098	0.098
Blended Income and Sales Approach [Member] | Measurement Input, Cap Rate [Member] | Weighted Average [Member]
Impaired loans, Measurement Input	0.075	0.072
Blended Income and Sales Approach [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	0.15	0.15
Blended Income and Sales Approach [Member] | Measurement Input, Loss Severity [Member] | Weighted Average [Member]
Impaired loans, Measurement Input	0.15	0.15
Blended Income and Sales Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Minimum [Member]
Impaired loans, Measurement Input	(0.3)	(0.3)
Blended Income and Sales Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Maximum [Member]
Impaired loans, Measurement Input	0.25	0.25
Blended Income and Sales Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Weighted Average [Member]
Impaired loans, Measurement Input	0.012	0.012
Blended Income and Sales Approach [Member] | Fair Value, Measurements, Nonrecurring [Member]
Impaired loans	$ 2,915	$ 4,206