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Note 2 - Allowance for Doubtful Accounts Receivable (Tables)
 12 Months Ended
Dec. 31, 2017
Notes Tables  
Allowance for Credit Losses on Financing Receivables [Table Text Block]
   
201
7
    
201
6
    
201
5
  
Balance at the beginning of yea
r
   $
1,276
     $
848
     $
680
  
                         
Provision for bad debt
s
    
1,002
      
523
      
266
  
                         
Charge-off
s
    
(901
 )    
(96
 )    
(98
 )
                         
Recoverie
s
    
5
      
1
      
-
  
                         
Balance at the end of yea
r
   $
1,382
     $
1,276
     $
848