Note 6 - Investment Securities - The Amortized Cost and Estimated Fair Value of the Securities Portfolio by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Available-for-sale, amortized cost, due in one year or less	$ 46,954
Available-for-sale, estimated fair value, due in one year or less	46,994
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	84,708
Available-for-sale, estimated fair value, due after one year through five years	84,923
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	80,396
Available-for-sale, estimated fair value, due after five years through ten years	79,302
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	621
Available-for-sale, amortized cost, due after ten years	21,101
Available-for-sale, estimated fair value, due after ten years	20,652
Held-to-maturity, amortized cost, due after ten years	2,905
Held-to-maturity, estimated fair value, due after ten years	2,979
Available-for-sale, amortized cost, mortgage-backed securities	262,627
Available-for-sale, estimated fair value, mortgage-backed securities	260,174
Held-to-maturity, amortized cost, mortgage-backed securities	0
Held-to-maturity, estimated fair value, mortgage-backed securities	0
Available-for-sale, amortized cost	495,786
Available-for-sale, estimated fair value	492,045
Held-to-maturity, amortized cost	3,475	$ 3,488
Held-to-maturity, estimated fair value	$ 3,600	$ 3,597