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Note 3 - Investments (Details Textual) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Available-for-sale Securities, Current, Total $ 0 $ 335,000
Debt Securities, Available-for-sale, Gain (Loss), Total (62,000) 231,000
Debt Securities, Available-for-sale, Unrealized Gain (Loss), Total 98,000 170,000
Debt Securities, Available-for-sale, Realized Loss $ 160,000  
Debt Securities, Available-for-sale, Realized Gain   $ 61,000