Note 4 - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Due in one year or less, Fair value	$ 9,925
Due after one year through five years, Fair value	206,877
Due after five years through ten years, Fair value	133,454
Due after ten years, Fair value	24,314
Equity securities, Fair value	4,975
Total investment securities available-for-sale, Fair value	379,545	$ 390,475
Due in one year or less, Amortized cost	9,924
Due after one year through five years, Amortized cost	210,575
Due after five years through ten years, Amortized cost	135,725
Due after ten years, Amortized cost	24,216
Equity securities, Amortized cost	5,296
Investment securities available-for-sale, amortized cost	$ 385,736	$ 396,168