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Fair Value of Financial Instruments and Concentrations of Credit Risk (Details Textual)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
customer
Dec. 31, 2016
USD ($)
customer
Dec. 31, 2015
customer
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Increase (decrease) trade receivables $ 94.3    
Increase (decrease) in trade receivables, percent 58.00%    
Number of major customers | customer 20 20,000 20,000
Receivables, net [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Increase (decrease) in income taxes receivable   $ 38.0  
Nontrade receivables $ 10.8 11.5  
Environmental services [Member] | Receivables, net [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Escrow deposit $ 8.0 $ 8.0  
Sonatrach [Member] | Customer concentration risk [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Concentration risk, percentage   14.00%  
Sales revenue, net [Member] | Twenty largest customers [Member] | Customer concentration risk [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Concentration risk, percentage 45.00% 53.00% 49.00%
Convertible Notes due 2021 [Member] | Senior notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt, fair value $ 127.3 $ 110.5  
Convertible Notes due 2017 [Member] | Senior notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt, fair value   $ 84.4