Note 4 - Investment Securities - Investment Securities by Contractual Maturity (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
After one year through five years, amortized cost	$ 3,142,000
After one year through five years, estimated fair value	3,243,000
After five years through ten years, amortized cost	6,178,000
After five years through ten years, estimated fair value	6,370,000
After ten years, amortized cost	23,150,000
After ten years, estimated fair value	24,029,000
Amortized cost	156,410,000
Estimated fair value	159,320,000	$ 171,507,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Government-sponsored mortgage-backed securities, amortized cost	123,940,000
Government-sponsored mortgage-backed securities, estimated fair value	$ 125,678,000