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, 2017	Dec. 31, 2016
Impaired Loans [Member]
Assets, fair value, nonrecurring	$ 2,274	$ 6,952
Other Real Estate [Member]
Assets, fair value, nonrecurring	2,231	2,505
Fair Value, Inputs, Level 3 [Member] | Impaired Loans [Member]
Assets, fair value, nonrecurring	2,274	6,952
Fair Value, Inputs, Level 3 [Member] | Other Real Estate [Member]
Assets, fair value, nonrecurring	2,231	2,505
Available-for-sale Securities [Member]
Assets, fair value, recurring	341,932	323,658
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	341,355	323,082
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value, recurring	577	576
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	335,451	319,097
US Government Agencies Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	335,451	319,097
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	4,456	4,561
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	3,879	3,985
US States and Political Subdivisions Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, fair value, recurring	577	$ 576
Corporate Debt Securities [Member] | Available-for-sale Securities [Member]
Assets, fair value, recurring	2,025
Corporate Debt Securities [Member] | Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, fair value, recurring	$ 2,025