Note 3 - Investment Securities - The Amortized Cost and Estimated Fair Value of the Securities Portfolio by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale, amortized cost, due in one year or less	$ 19,743
Available-for-sale, estimated fair value, due in one year or less	19,762
Held-to-maturity, amortized cost, due in one year or less	0
Held-to-maturity, estimated fair value, due in one year or less	0
Available-for-sale, amortized cost, due after one year through five years	87,628
Available-for-sale, estimated fair value, due after one year through five years	87,504
Held-to-maturity, amortized cost, due after one year through five years	0
Held-to-maturity, estimated fair value, due after one year through five years	0
Available-for-sale, amortized cost, due after five years through ten years	85,007
Available-for-sale, estimated fair value, due after five years through ten years	83,317
Held-to-maturity, amortized cost, due after five years through ten years	570
Held-to-maturity, estimated fair value, due after five years through ten years	630
Available-for-sale, amortized cost, due after ten years	20,183
Available-for-sale, estimated fair value, due after ten years	19,528
Held-to-maturity, amortized cost, due after ten years	2,918
Held-to-maturity, estimated fair value, due after ten years	2,967
Available-for-sale, amortized cost, mortgage-backed securities	272,653
Available-for-sale, estimated fair value, mortgage-backed securities	269,920
Held-to-maturity, amortized cost, mortgage-backed securities	0
Held-to-maturity, estimated fair value, mortgage-backed securities	0
Available-for-sale, amortized cost	485,214
Available-for-sale, estimated fair value	480,031
Held-to-maturity, amortized cost	3,488	$ 3,611
Held-to-maturity, estimated fair value	$ 3,597	$ 3,809