Note 6 - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Due in one year or less, Fair value	$ 9,443
Due after one year through five years, Fair value	198,468
Due after five years through ten years, Fair value	119,065
Due after ten years, Fair value	20,416
Total investment securities available-for-sale, Fair value	347,392	$ 374,570
Due in one year or less, Amortized cost	9,431
Due after one year through five years, Amortized cost	206,465
Due after five years through ten years, Amortized cost	124,327
Due after ten years, Amortized cost	21,074
Investment securities available-for-sale, debt securities amortized cost	$ 361,297	$ 380,440

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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