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Receivables (Details Textual) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Increase in trade receivables $ 55,800    
Increase in trade receivables, percent 34.00%    
Gross trade receivables $ 218,335   $ 162,569
Other receivables $ 17,994   20,643
Sales revenue, net | Customer concentration risk | Sonatrach      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Concentration risk, percentage 10.00% 15.00%  
Receivables, net      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Income taxes receivable     38,000
Nontrade receivables $ 9,600   11,500
Receivables, net | Escrow | Environmental services      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Other receivables $ 8,000   $ 8,000