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Schedule II - Valuation and Qualifying Accounts (Tables)
 12 Months Ended
Dec. 31, 2019
Notes Tables  
Summary of Allowance for Doubtful Accounts and Revenue Adjustments [Table Text Block]
    2019   2018   2017
Balance at beginning of year   $
564
     $
652
     $
567
  
Provision for bad debt    
(52
 )    
(50
 )    
116
  
Write-offs, net of recoveries    
(26
 )    
(38
 )    
(31
 )
Balance at end of year   $
486
     $
564
     $
652