Note 11 - Fair Value of Financial Instruments and Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Recurring Securities Available for Sale	$ 357,889	$ 353,066
US Government Agencies Debt Securities [Member]
Recurring Securities Available for Sale	351,138	346,205
US States and Political Subdivisions Debt Securities [Member]
Recurring Securities Available for Sale	3,895	3,989
Corporate Debt Securities [Member]
Recurring Securities Available for Sale	2,856	2,872
Fair Value, Recurring [Member]
Recurring Securities Available for Sale	357,889	353,066
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale	353,992	348,789
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Recurring Securities Available for Sale	3,897	4,277
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Recurring Securities Available for Sale	351,138	346,205
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale	347,456	342,142
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Recurring Securities Available for Sale	3,682	4,063
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Recurring Securities Available for Sale	3,895	3,989
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale	3,680	3,775
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Recurring Securities Available for Sale	215	214
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Recurring Securities Available for Sale	2,856	2,872
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale	2,856	2,872
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Recurring Securities Available for Sale
Fair Value, Nonrecurring [Member]
Impaired Loans	1,708	3,352
Other Real Estate	1,123	1,183
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Impaired Loans
Other Real Estate
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Impaired Loans
Other Real Estate
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Impaired Loans	1,708	3,352
Other Real Estate	$ 1,123	$ 1,183