Note 3 - Investment Securities - Scheduled Maturities of Investment Securities Available-for-sale and Held-to-maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale, maturing within one year, amortized cost	$ 378
Available-for-sale, maturing within one year, estimated fair value	382
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	20,702
Available-for-sale, maturing after one to five years, estimated fair value	20,550
Held-to-maturity, maturing after one to five years, amortized cost	1,986
Held-to-maturity, maturing after one to five years, estimated fair value	1,991
Available-for-sale, maturing after five to ten years, amortized cost	61,139
Available-for-sale, maturing after five to ten years, estimated fair value	60,557
Held-to-maturity, maturing after five to ten years, amortized cost	4,298
Held-to-maturity, maturity after five to ten years, estimated fair value	4,253
Available-for-sale, maturing after ten years, amortized cost	73,254
Available-for-sale, maturing after ten years, estimated fair value	72,382
Held-to-maturity, maturing after ten years, amortized cost	19,995
Held-to-maturity, maturing after ten years, estimated fair value	19,705
Available-for-sale, amortized cost	155,473	$ 184,278
Available-for-sale, estimated fair value	153,871	181,910
Held-to-maturity, amortized cost	26,279	25,904
Held-to-maturity, estimated fair value	$ 25,949	$ 25,508