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Note 4 - Investments (Details Textual) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Marketable Securities, Total $ 0   $ 0  
Proceeds from Sale and Maturity of Marketable Securities, Total 0      
Debt Securities, Available-for-sale, Realized Gain (Loss), Total   $ (24,000)   $ 35,000
Debt Securities, Available-for-sale, Unrealized Gain (Loss), Total   (42,000)   (77,000)
Debt Securities, Available-for-sale, Realized Gain   18,000    
Debt Securities, Available-for-sale, Gain (Loss), Total $ 0 $ (24,000) $ 0 $ (42,000)