Note 4 - Investments (Details Textual) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	[1]
Available-for-sale Securities, Current, Total	$ 173,000		$ 173,000		$ 335,000
Proceeds from Sale and Maturity of Marketable Securities, Total		$ 0
Debt Securities, Available-for-sale, Realized Gain (Loss), Total	(24,000)		35,000	$ 55,000
Debt Securities, Available-for-sale, Unrealized Gain (Loss), Total	(42,000)		(77,000)	168,000
Debt Securities, Available-for-sale, Realized Gain	18,000
Debt Securities, Available-for-sale, Gain (Loss), Total	$ (24,000)	$ (387,000)	$ (42,000)	$ 223,000

[1] The condensed consolidated balance sheet as of December 31, 2019 has been prepared using information from the audited consolidated balance sheet as of that date.