Note 3 - Investment Securities - Scheduled Maturities of Investment Securities Available-for-sale and Held-to-maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale, maturing within one year, amortized cost	$ 490
Available-for-sale, maturing within one year, estimated fair value	496
Held-to-maturity, maturing within one year, amortized cost
Held-to-maturity, maturing within one year, estimated fair value
Available-for-sale, maturing after one to five years, amortized cost	8,674
Available-for-sale, maturing after one to five years, estimated fair value	8,723
Held-to-maturity, maturing after one to five years, amortized cost	2,048
Held-to-maturity, maturing after one to five years, estimated fair value	2,079
Available-for-sale, maturing after five to ten years, amortized cost	71,462
Available-for-sale, maturing after five to ten years, estimated fair value	71,596
Held-to-maturity, maturing after five to ten years, amortized cost	2,904
Held-to-maturity, maturity after five to ten years, estimated fair value	2,899
Available-for-sale, maturing after ten years, amortized cost	78,050
Available-for-sale, maturing after ten years, estimated fair value	77,610
Held-to-maturity, maturing after ten years, amortized cost	22,425
Held-to-maturity, maturing after ten years, estimated fair value	22,325
Available-for-sale, amortized cost	158,676	$ 184,278
Available-for-sale, estimated fair value	158,425	181,910
Held-to-maturity, amortized cost	27,377	25,904
Held-to-maturity, estimated fair value	$ 27,303	$ 25,508