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Note 4 - Accounts Receivable (Details Textual) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss, Noncurrent $ 1,720,000 $ 1,720,000
Percentage of Remaining Balance Owned Reserved 100.00% 100.00%