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Note 3 - Revenue From Contracts With Customers (Details Textual) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Capitalized Contract Cost, Amortization Period 4 years  
Contract with Customer, Liability, Revenue Recognized $ 76,000 $ 0
Contract with Customer, Liability, Total $ 333,240 $ 196,609