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, 2017	Dec. 31, 2016
Available for sale securities, fair value	$ 338,249	$ 323,658
Fair Value, Measurements, Recurring [Member]
Available for sale securities, fair value	338,249	323,658
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available for sale securities, fair value	338,019	323,082
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Available for sale securities, fair value	230	576
Fair Value, Measurements, Nonrecurring [Member]
Impaired Loans	6,446	6,952
Other Real Estate	1,625	2,505
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Impaired Loans	6,446	6,952
Other Real Estate	1,625	2,505
US Government Agencies Debt Securities [Member]
Available for sale securities, fair value	330,658	319,097
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available for sale securities, fair value	330,658	319,097
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available for sale securities, fair value	330,658	319,097
US States and Political Subdivisions Debt Securities [Member]
Available for sale securities, fair value	4,539	4,561
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available for sale securities, fair value	4,539	4,561
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available for sale securities, fair value	4,309	3,985
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Available for sale securities, fair value	230	$ 576
Corporate Debt Securities [Member]
Available for sale securities, fair value	2,060
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available for sale securities, fair value	2,060
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available for sale securities, fair value	2,060
Asset-backed Securities [Member]
Available for sale securities, fair value	992
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available for sale securities, fair value	992
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available for sale securities, fair value	$ 992