Note 6 - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Due in one year or less, Fair value	$ 6,938
Due after one year through five years, Fair value	185,003
Due after five years through ten years, Fair value	131,117
Due after ten years, Fair value	21,136
Total investment securities available-for-sale, Fair value	344,194	$ 374,570
Due in one year or less, Amortized cost	6,922
Due after one year through five years, Amortized cost	191,920
Due after five years through ten years, Amortized cost	135,913
Due after ten years, Amortized cost	21,574
Investment securities available-for-sale, debt securities amortized cost	$ 356,329	$ 380,440