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FINANCIAL RISK MANAGEMENT (Credit risk narrative) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Disclosure of credit risk exposure [line items]    
Trade receivables $ 1,011,430  
Credit risk    
Disclosure of credit risk exposure [line items]    
Financial assets, investments assessed as investment grade, percent 75.70% 65.70%
Trade receivables $ 1,011,400 $ 635,000
Allowance for doubtful account 16,500 6,000
Financing Receivables, Equal to Greater than 1 Day Past Due | Credit risk    
Disclosure of credit risk exposure [line items]    
Trade receivables 117,300 69,100
Performing Financial Instruments | Credit risk    
Disclosure of credit risk exposure [line items]    
Trade receivables 910,700 571,900
Performance Guarantee | Credit risk    
Disclosure of credit risk exposure [line items]    
Trade receivables 2,600 2,400
Credit Insurance | Credit risk    
Disclosure of credit risk exposure [line items]    
Trade receivables 380,000 326,900
Guarantee Type, Other | Credit risk    
Disclosure of credit risk exposure [line items]    
Trade receivables $ 15,000 $ 7,600