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)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Measurements, Nonrecurring [Member]
Impaired loans	$ 14,102,000	$ 16,027,000
Other Repossessed Assets	$ 35,000
Valuation, Income Approach [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	0.15	0.15
Valuation, Income Approach [Member] | Minimum [Member] | Measurement Input, Cap Rate [Member]
Impaired loans, Measurement Input	0.065	0.065
Valuation, Income Approach [Member] | Maximum [Member] | Measurement Input, Cap Rate [Member]
Impaired loans, Measurement Input	0.075	0.075
Valuation, Income Approach [Member] | Weighted Average [Member] | Measurement Input, Cap Rate [Member]
Impaired loans, Measurement Input	0.07	0.068
Valuation, Income Approach [Member] | Weighted Average [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	0.15	0.15
Valuation, Income Approach [Member] | Fair Value, Measurements, Nonrecurring [Member]
Impaired loans	$ 1,531,000	$ 1,818,000
Valuation, Market Approach [Member] | Measurement Input, Loss Severity [Member]
Other repossesed assets, Measurement Input	0.15
Valuation, Market Approach [Member] | Minimum [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	(0.406)	(0.309)
Valuation, Market Approach [Member] | Minimum [Member] | Measurement Input, Comparability Adjustment [Member]
Impaired loans, Measurement Input	(0.5)	(0.5)
Valuation, Market Approach [Member] | Maximum [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	0.15	0.15
Valuation, Market Approach [Member] | Maximum [Member] | Measurement Input, Comparability Adjustment [Member]
Impaired loans, Measurement Input	0.162	0.162
Valuation, Market Approach [Member] | Weighted Average [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	0.104	0.087
Other repossesed assets, Measurement Input	0.15
Valuation, Market Approach [Member] | Weighted Average [Member] | Measurement Input, Comparability Adjustment [Member]
Impaired loans, Measurement Input	(0.015)	(0.008)
Valuation, Market Approach [Member] | Fair Value, Measurements, Nonrecurring [Member]
Impaired loans	$ 8,655,000	$ 10,003
Other Repossessed Assets	$ 35,000
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] | Minimum [Member] | Measurement Input, Cap Rate [Member]
Impaired loans, Measurement Input	0.05	0.05
Blended Income and Sales Approach [Member] | Minimum [Member] | Measurement Input, Comparability Adjustment [Member]
Impaired loans, Measurement Input	(0.3)	(0.3)
Blended Income and Sales Approach [Member] | Maximum [Member] | Measurement Input, Cap Rate [Member]
Impaired loans, Measurement Input	0.098	0.098
Blended Income and Sales Approach [Member] | Maximum [Member] | Measurement Input, Comparability Adjustment [Member]
Impaired loans, Measurement Input	0.25	0.25
Blended Income and Sales Approach [Member] | Weighted Average [Member] | Measurement Input, Cap Rate [Member]
Impaired loans, Measurement Input	0.071	0.072
Blended Income and Sales Approach [Member] | Weighted Average [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	0.15	0.15
Blended Income and Sales Approach [Member] | Weighted Average [Member] | Measurement Input, Comparability Adjustment [Member]
Impaired loans, Measurement Input	(0.008)	(0.012)
Blended Income and Sales Approach [Member] | Fair Value, Measurements, Nonrecurring [Member]
Impaired loans	$ 3,916,000	$ 4,206,000