Note 11 - 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, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Other real estate owned	$ 239,000	$ 0	$ 0	$ 0	$ 638,000	$ 0
Fair Value, Nonrecurring [Member]
Impaired loans	1,458,000		$ 4,111,000
Impaired loans, Measurement Input			10.4
Fair Value, Nonrecurring [Member] | Valuation, Market Approach [Member]
Impaired loans			$ 2,724,000
Fair Value, Nonrecurring [Member] | Valuation, Market Approach [Member] | Measurement Input, Loss Severity [Member]
Impaired loans	$ 896,000
Impaired loans, Measurement Input	0.592
Other repossessed assets			$ 35,000
Other repossessed assets, Measurement Input			0.0
Fair Value, Nonrecurring [Member] | Valuation, Market Approach [Member] | Measurement Input, Loss Severity [Member] | Minimum [Member]
Impaired loans, Measurement Input	0.466		(0.365)
Fair Value, Nonrecurring [Member] | Valuation, Market Approach [Member] | Measurement Input, Loss Severity [Member] | Maximum [Member]
Impaired loans, Measurement Input	0.898		0.150
Fair Value, Nonrecurring [Member] | Valuation, Market Approach [Member] | Measurement Input, Comparability Adjustment [Member]
Impaired loans, Measurement Input			0.000
Other real estate owned	$ 239,000
Other real estate owned, Measurement Input	0.065
Fair Value, Nonrecurring [Member] | Valuation, Market Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Minimum [Member]
Impaired loans, Measurement Input			0.0
Other real estate owned, Measurement Input	0.005
Fair Value, Nonrecurring [Member] | Valuation, Market Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Maximum [Member]
Other real estate owned, Measurement Input	0.125
Fair Value, Nonrecurring [Member] | Valuation, Income Approach [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input			0.150
Fair Value, Nonrecurring [Member] | Valuation, Income Approach [Member] | Measurement Input, Loss Severity [Member] | Minimum [Member]
Impaired loans, Measurement Input			15.0
Fair Value, Nonrecurring [Member] | Valuation, Income Approach [Member] | Measurement Input, Cap Rate [Member]
Impaired loans			$ 204,000
Impaired loans, Measurement Input			0.085
Fair Value, Nonrecurring [Member] | Valuation, Income Approach [Member] | Measurement Input, Cap Rate [Member] | Minimum [Member]
Impaired loans, Measurement Input			8.5
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member]
Impaired loans			$ 1,183,000
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Minimum [Member]
Impaired loans, Measurement Input			15.0
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Measurement Input, Loss Severity [Member]
Impaired loans, Measurement Input	0.150		0.150
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Measurement Input, Loss Severity [Member] | Minimum [Member]
Impaired loans, Measurement Input	0.150
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Measurement Input, Cap Rate [Member]
Impaired loans, Measurement Input	0.092		8.7
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Measurement Input, Cap Rate [Member] | Minimum [Member]
Impaired loans, Measurement Input	0.090		0.074
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Measurement Input, Cap Rate [Member] | Maximum [Member]
Impaired loans, Measurement Input	0.095		0.098
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Measurement Input, Comparability Adjustment [Member]
Impaired loans	$ 562,000
Impaired loans, Measurement Input	(0.032)		(7.8)
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Minimum [Member]
Impaired loans, Measurement Input	(0.150)		(0.300)
Fair Value, Nonrecurring [Member] | Blended Income and Sales Approach [Member] | Measurement Input, Comparability Adjustment [Member] | Maximum [Member]
Impaired loans, Measurement Input	0.150		0.100