Note 9 - Quantitative Information about Assets Measured at Fair Value (Details) - USD ($) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2018		Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements		$ 452		$ 1,101
Impaired Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements		446		1,067
Mortgage Servicing Rights [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements		6		34
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements		452		1,101
Fair Value, Inputs, Level 3 [Member] | Impaired Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements		446		1,067
Fair Value, Inputs, Level 3 [Member] | Mortgage Servicing Rights [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements		6		34
Fair Value, Inputs, Level 3 [Member] | Appraisal Valuation Technique [Member] | Impaired Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements	[1]	$ 299		$ 943
Nonrecurring fair value liquidation inputs	[2]	(10.00%)	[1]	(10.00%)
Fair Value, Inputs, Level 3 [Member] | Appraisal Valuation Technique [Member] | Impaired Loans [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value range of value inputs	[3]	(20.00%)	[1]	(15.00%)
Fair Value, Inputs, Level 3 [Member] | Appraisal Valuation Technique [Member] | Impaired Loans [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value range of value inputs	[3]	(80.00%)	[1]	(90.00%)
Fair Value, Inputs, Level 3 [Member] | Market Approach Valuation Technique [Member] | Impaired Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements	[4]	$ 147		$ 124
Fair Value, Inputs, Level 3 [Member] | Market Approach Valuation Technique [Member] | Impaired Loans [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value range of value inputs	[4]	(20.00%)		(25.00%)
Fair Value, Inputs, Level 3 [Member] | Market Approach Valuation Technique [Member] | Impaired Loans [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value range of value inputs	[4]	(50.00%)		(50.00%)
Fair Value, Inputs, Level 3 [Member] | Discounted Cash Flow Valuation Technique [Member] | Mortgage Servicing Rights [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value measurements		$ 6		$ 34
Nonrecurring fair value range of value inputs		12.50%
Fair Value, Inputs, Level 3 [Member] | Discounted Cash Flow Valuation Technique [Member] | Mortgage Servicing Rights [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value range of value inputs				13.00%
Nonrecurring fair value expected term		2 years		2 years
Fair Value, Inputs, Level 3 [Member] | Discounted Cash Flow Valuation Technique [Member] | Mortgage Servicing Rights [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Nonrecurring fair value range of value inputs				15.00%
Nonrecurring fair value expected term		27 years		26 years

[1] Fair value is primarily determined through appraisals of the underlying collateral by independent parties, which generally includes various level 3 inputs which are not always identifiable.

[2] Appraisals and pending agreements of sale are adjusted by management for estimated liquidation expenses. The range is presented as a percent of the initial appraised value.

[3] Appraisals may be adjusted by management for qualitative factors such as economic conditions and the age of the appraisal. The range is presented as a percent of the initial appraised value.

[4] Values obtained from financial statements for UCC collateral (fixed assets and inventory) are discounted to estimated realizable liquidation value.