Note 3 - Available-for-sale Securities - Investment Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale securities in continuous loss position, less than 12 months, fair value	$ 7,724	$ 8,024
Available-for-sale securities in continuous loss position, less than 12 months, unrealized loss	(62)	(38)
Available-for-sale securities in continuous loss position, 12 months or more, fair value	17,081	18,396
Available-for-sale securities in continuous loss position, 12 months or more, unrealized loss	(886)	(1,184)
Available-for-sale securities in continuous loss position, fair value	24,805	26,420
Available-for-sale securities in continuous loss position, unrealized loss	(948)	(1,222)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available-for-sale securities in continuous loss position, less than 12 months, fair value	2,609	8,024
Available-for-sale securities in continuous loss position, less than 12 months, unrealized loss	(20)	(38)
Available-for-sale securities in continuous loss position, 12 months or more, fair value	3,919	5,422
Available-for-sale securities in continuous loss position, 12 months or more, unrealized loss	(48)	(158)
Available-for-sale securities in continuous loss position, fair value	6,528	13,446
Available-for-sale securities in continuous loss position, unrealized loss	(68)	(196)
Corporate Debt Securities [Member]
Available-for-sale securities in continuous loss position, less than 12 months, fair value
Available-for-sale securities in continuous loss position, less than 12 months, unrealized loss
Available-for-sale securities in continuous loss position, 12 months or more, fair value	13,162	12,974
Available-for-sale securities in continuous loss position, 12 months or more, unrealized loss	(838)	(1,026)
Available-for-sale securities in continuous loss position, fair value	13,162	12,974
Available-for-sale securities in continuous loss position, unrealized loss	(838)	$ (1,026)
SBA Loan Pools [Member]
Available-for-sale securities in continuous loss position, less than 12 months, fair value	5,115
Available-for-sale securities in continuous loss position, less than 12 months, unrealized loss	(42)
Available-for-sale securities in continuous loss position, 12 months or more, fair value
Available-for-sale securities in continuous loss position, 12 months or more, unrealized loss
Available-for-sale securities in continuous loss position, fair value	5,115
Available-for-sale securities in continuous loss position, unrealized loss	$ (42)