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Note 2 - Summary of Significant Accounting Policies (Details Textual)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
Jun. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
Jan. 01, 2019
USD ($)
Operating Lease, Right-of-Use Asset $ 515,000   $ 515,000     $ 629,000
Operating Lease, Liability, Total $ 520,000   $ 520,000     $ 629,000
Number of Financial Institutions 1   1      
Accounts Receivable, Allowance for Credit Loss, Ending Balance $ 469,000   $ 469,000   $ 284,000  
Contract with Customer, Asset, after Allowance for Credit Loss, Total 0   0   0  
Contract with Customer, Liability, Total 552,000   552,000   $ 686,000  
Equity Method Investment, Other than Temporary Impairment $ 0 $ 0 $ 0 $ 0    
Minimum [Member]            
Warranty Period     1 year      
Maximum [Member]            
Warranty Period     3 years      
Customer Concentration Risk [Member] | Revenue Benchmark [Member]            
Concentration Risk, Number of Customers 3 1 2 1    
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Three Customers [Member]            
Concentration Risk, Percentage 55.00%          
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | One Customer [Member]            
Concentration Risk, Percentage   13.00%   23.00%    
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Two Customers [Member]            
Concentration Risk, Percentage     32.00%      
Customer Concentration Risk [Member] | Accounts Receivable [Member]            
Concentration Risk, Number of Customers     4   3  
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Three Customers [Member]            
Concentration Risk, Percentage         54.00%  
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Four Customers [Member]            
Concentration Risk, Percentage     64.00%