Note 4 - Investment Securities - Scheduled Maturities of Investment Securities Available-for-sale and Held-to-maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale, maturing within one year, amortized cost	$ 1,083
Available-for-sale, maturing within one year, estimated fair value	1,084
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	36,800
Available-for-sale, maturing after one to five years, estimated fair value	36,227
Held-to-maturity, maturing after one to five years, amortized cost	1,081
Held-to-maturity, maturing after one to five years, estimated fair value	1,077
Available-for-sale, maturing after five to ten years, amortized cost	57,729
Available-for-sale, maturing after five to ten years, estimated fair value	56,065
Held-to-maturity, maturing after five to ten years, amortized cost	10,390
Held-to-maturity, maturity after five to ten years, estimated fair value	10,076
Available-for-sale, maturing after ten years, amortized cost	40,044
Available-for-sale, maturing after ten years, estimated fair value	39,111
Held-to-maturity, maturing after ten years, amortized cost	9,991
Held-to-maturity, maturing after ten years, estimated fair value	9,699
Available-for-sale, amortized cost	135,656	$ 155,473
Available-for-sale, estimated fair value	132,487	153,871
Held-to-maturity, amortized cost	21,462	26,279
Held-to-maturity, estimated fair value	$ 20,852	$ 25,949