Note 11 - Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands	Jun. 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	$ 302,850	$ 291,050
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	302,850	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	4,148	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	928	930
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	5,076	5,099
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	306,998	295,219
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value, recurring	928	930
Available-for-sale Securities [Member]
Assets, fair value, recurring	307,926	296,149
Fair Value, Inputs, Level 3 [Member] | Impaired Loans [Member]
Assets, fair value, nonrecurring	6,628	8,545
Fair Value, Inputs, Level 3 [Member] | Other Real Estate [Member]
Assets, fair value, nonrecurring	2,912	2,536
Impaired Loans [Member]
Assets, fair value, nonrecurring	6,628	8,545
Other Real Estate [Member]
Assets, fair value, nonrecurring	$ 2,912	$ 2,536