Note 3 - Investment Securities - Gross Unrealized Losses and Fair Value by Investment Category and Continuous Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Securities in continuous unrealized loss position, less than twelve months, number of securities		13
Securities in continuous unrealized loss position, less than twelve months, fair value		$ 36,119
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses		$ (187)
Securities in continuous unrealized loss position, twelve months or more, number of securities		8
Securities in continuous unrealized loss position, twelve months or more, fair value		$ 16,158
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses		$ (86)
Securities in continuous unrealized loss position, number of securities		21
Securities in continuous unrealized loss position, fair value		$ 52,277
Securities in continuous unrealized loss position, gross unrealized losses		$ (273)
US States and Political Subdivisions Debt Securities [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	1
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 509
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (1)
Securities in continuous unrealized loss position, twelve months or more, number of securities		1
Securities in continuous unrealized loss position, twelve months or more, fair value		$ 509
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses		$ (2)
Securities in continuous unrealized loss position, number of securities	1	1
Securities in continuous unrealized loss position, fair value	$ 509	$ 509
Securities in continuous unrealized loss position, gross unrealized losses	$ (1)	$ (2)
US Government Agencies Debt Securities [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities		6
Securities in continuous unrealized loss position, less than twelve months, fair value		$ 16,116
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses		$ (83)
Securities in continuous unrealized loss position, twelve months or more, number of securities		6
Securities in continuous unrealized loss position, twelve months or more, fair value		$ 13,938
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses		$ (81)
Securities in continuous unrealized loss position, number of securities		12
Securities in continuous unrealized loss position, fair value		$ 30,054
Securities in continuous unrealized loss position, gross unrealized losses		$ (164)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities		7
Securities in continuous unrealized loss position, less than twelve months, fair value		$ 20,003
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses		$ (104)
Securities in continuous unrealized loss position, twelve months or more, number of securities		1
Securities in continuous unrealized loss position, twelve months or more, fair value		$ 1,711
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses		$ (3)
Securities in continuous unrealized loss position, number of securities		8
Securities in continuous unrealized loss position, fair value		$ 21,714
Securities in continuous unrealized loss position, gross unrealized losses		$ (107)