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Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2014
Long-term Investment Marketable Period 1 year      
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities $ 0 $ 0 $ 0  
Average Maturity Period of Interest Rate of Auction Securities 1 year 180 days      
Inventories Estimated Useful Lives 2 years      
Inventory, Finished Goods, Gross $ 2,400,000 2,300,000    
Depreciation 841,000 734,000 562,000  
Impairment of Long-Lived Assets Held-for-use 0      
Impairment of Intangible Assets (Excluding Goodwill) 650,000  
Sales Revenue, Services, Net 19,028,000 17,739,000 17,839,000 $ 17,800,000
Advertising Expense $ 1,300,000 $ 1,200,000 $ 1,600,000  
Uncertain Income Tax Position Minimum Rate 50.00%      
Number of Operating Segments 1      
Disclosure on Geographic Areas Long Lived Assets in Entity S Country of Domicile, Percent 98.00%      
End-Customers [Member]        
Standard Warranty Period 1 year      
Minimum [Member]        
Finite-Lived Intangible Asset, Useful Life 330 days      
Minimum [Member] | Distributors [Member]        
Standard Warranty Period 1 year 60 days      
Maximum [Member]        
Finite-Lived Intangible Asset, Useful Life 10 years      
Maximum [Member] | Distributors [Member]        
Standard Warranty Period 1 year 120 days      
Customer Concentration Risk [Member] | Accounts Receivable [Member]        
Concentration Risk, Percentage 12.00% 10.00%    
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | UNITED STATES        
Concentration Risk, Percentage 55.00% 52.00% 45.00%  
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Outside the United States [Member]        
Concentration Risk, Percentage 45.00% 48.00% 55.00%