Note 4 - Realized Gain (Loss) on Investments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Gross realized gains	$ 18,000	$ 28,000	$ 169,000
Gross realized losses	0	(4,000)	(195,000)
Other-than-temporary impairment	0	0	0
Total net gains (losses) on AFS debt securities	$ 18,000	$ 24,000	$ (26,000)