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Note 3 - Concentration of Credit Risk (Details Textual)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2019
USD ($)
Sep. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Cash and Cash Equivalents, at Carrying Value, Ending Balance $ 6,739,065 $ 14,192,180 $ 6,739,065 $ 14,192,180 $ 11,439,361 $ 14,210,909
Cash Equivalents, at Carrying Value, Total 5,800,000   5,800,000   8,900,000  
Cash, Uninsured Amount $ 5,017,000   $ 5,017,000   $ 6,920,000  
Customer Concentration Risk [Member] | Revenue Benchmark [Member]            
Number Of Major Customers 2   2      
Concentration Risk, Percentage 42.80% 27.10% 28.10% 34.70%    
Customer Concentration Risk [Member] | Accounts Receivable [Member]            
Number Of Major Customers     2   2  
Concentration Risk, Percentage     47.90%   42.00%