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Supplementary cash flow information (Tables)
 12 Months Ended
Dec. 31, 2017
Statement [Line Items]  
Disclosure of detailed information about supplemental cash flow information [Table Text Block]
      Year ended  
      December 31,  
      2017     2016  
               
  Change in:            
       Trade and other receivables $ (8,979 ) $ 68,270  
       Other financial assets/liabilities   6,620     19,181  
       Inventories   (18,690 )   2,653  
       Prepaid expenses and other current assets   (4,619 )   3,646  
       Trade and other payables   (6,336 )   (8,339 )
       Changes in taxes payable/receivable   39,326     3,666  
       Other   1,693     (1,871 )
               
    $ 9,015   $ 87,206