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Note 2 - Certificates of Deposit (Details Textual) - USD ($)
9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Certificates Of Deposit Maximum Value Per Deposit $ 250,000    
Certificates of Deposit, at Carrying Value, Current and Noncurrent 3,173,000   $ 4,095,000
Payments to Acquire Investments, Total 4,365  
Certificates of Deposit [Member]      
Payments to Acquire Investments, Total 1,468,000 3,145,000  
Proceeds from Sale, Maturity and Collection of Investments, Total $ 2,390,000 $ 2,662,890