Note 3 - Investment Securities Available for Sale - Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Within one year, amortized cost	$ 120
Within one year, estimated fair value	120
After one year through five years, amortized cost	3,903
After one year through five years, estimated fair value	4,076
After five years through ten years, amortized cost	5,552
After five years through ten years, estimated fair value	5,893
After ten years, amortized cost	30,950
After ten years, estimated fair value	32,488
Amortized cost	151,850
Estimated fair value	158,002	$ 159,320
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Investment securities not due at a single maturity date, amortized cost	5,400
Investment securities not due at a single maturity date, estimated fair value	5,416
Commercial Mortgage Backed Securities Issued by US Government Agencies [Member]
Investment securities not due at a single maturity date, amortized cost	105,925
Investment securities not due at a single maturity date, estimated fair value	$ 110,009