Note 6 - Investment Securities - The Amortized Cost and Estimated Fair Value of the Securities Portfolio by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale, amortized cost, due in one year or less	$ 32,117
Available-for-sale, estimated fair value, due in one year or less	32,149
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	72,712
Available-for-sale, estimated fair value, due after one year through five years	73,016
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	84,313
Available-for-sale, estimated fair value, due after five years through ten years	84,005
Held-to-maturity, amortized cost, due after five years through ten years	1,302
Held-to-maturity, estimated fair value, due after five years through ten years	1,407
Available-for-sale, amortized cost, due after ten years	24,475
Available-for-sale, estimated fair value, due after ten years	24,586
Held-to-maturity, amortized cost, due after ten years	2,159
Held-to-maturity, estimated fair value, due after ten years	2,210
Available-for-sale, amortized cost, mortgage-backed securities	250,828
Available-for-sale, estimated fair value, mortgage-backed securities	248,989
Held-to-maturity, amortized cost, mortgage-backed securities	0
Held-to-maturity, estimated fair value, mortgage-backed securities	0
Available-for-sale, amortized cost	464,445
Available-for-sale, estimated fair value	462,745
Held-to-maturity, amortized cost	3,461	$ 3,488
Held-to-maturity, estimated fair value	$ 3,617	$ 3,597