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Note 3 - Investments (Details Textual) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Available-for-sale Securities, Current, Total $ 258,000 $ 343,000
Proceeds from Sale and Maturity of Marketable Securities, Total   0
Debt Securities, Available-for-sale, Realized Gain (Loss), Total (50,000)
Debt Securities, Available-for-sale, Realized Loss 57,000  
Debt Securities, Available-for-sale, Realized Gain 7,000  
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax (254,000)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax   $ 10,000