Note 3 - Investment Securities (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Maturity Period of Mutual Funds (Year)	1 year
Term of Mutual Fund (Month)	180 days
Percentage of Holdings Non-investment Grade Rated	0.00%
Realized Investment Gains (Losses), Total	$ (412)
Mutual Fund [Member] | Fitch, AAA Rating [Member]
Percentage of Investment Holdings Grade Rated	24.00%