Note 4 - Investments (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Available-for-sale Securities, Current, Total	$ 228,000		$ 335,000
Debt Securities, Available-for-sale, Realized Gain (Loss), Total	(59,000)	$ 170,000
Debt Securities, Available-for-sale, Unrealized Gain (Loss), Total	(76,000)	167,000
Debt Securities, Available-for-sale, Realized Gain (Loss), Total	$ 17,000	$ 3,000