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, 2016	Dec. 31, 2015
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	$ 281,381	$ 291,050
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	281,381	291,050
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	4,112	4,169
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value, recurring	596	930
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	4,708	5,099
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	285,493	295,219
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value, recurring	596	930
Available-for-sale Securities [Member]
Assets, fair value, recurring	286,089	296,149
Fair Value, Inputs, Level 3 [Member] | Impaired Loans [Member]
Assets, fair value, nonrecurring	6,662	8,545
Fair Value, Inputs, Level 3 [Member] | Other Real Estate [Member]
Assets, fair value, nonrecurring	2,850	2,536
Impaired Loans [Member]
Assets, fair value, nonrecurring	6,662	8,545
Other Real Estate [Member]
Assets, fair value, nonrecurring	$ 2,850	$ 2,536