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	Sep. 30, 2018	Dec. 31, 2017
Recurring Securities Available for Sale	$ 318,032	$ 354,247
Fair Value, Measurements, Recurring [Member]
Recurring Securities Available for Sale	318,032	354,247
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale	311,402	346,949
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Recurring Securities Available for Sale	6,630	7,298
Fair Value, Measurements, Nonrecurring [Member]
Impaired Loans	5,185	4,876
Other Real Estate	1,468	2,015
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Impaired Loans
Other Real Estate
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Impaired Loans
Other Real Estate
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Impaired Loans	5,185	4,876
Other Real Estate	1,468	2,015
US Government Agencies Debt Securities [Member]
Recurring Securities Available for Sale	311,178	346,723
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Recurring Securities Available for Sale	311,178	346,723
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale	306,763	341,701
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Recurring Securities Available for Sale	4,415	5,022
US States and Political Subdivisions Debt Securities [Member]
Recurring Securities Available for Sale	3,972	4,493
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Recurring Securities Available for Sale	3,972	4,493
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale	3,757	4,277
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Recurring Securities Available for Sale	215	216
Corporate Debt Securities [Member]
Recurring Securities Available for Sale	2,882	2,060
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Recurring Securities Available for Sale	2,882	2,060
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale	882
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Recurring Securities Available for Sale	$ 2,000	2,060
Asset-backed Securities [Member]
Recurring Securities Available for Sale		971
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Recurring Securities Available for Sale		971
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Recurring Securities Available for Sale
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Recurring Securities Available for Sale		$ 971