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DERIVATIVES AND RISK MANAGEMENT ACTIVITIES Table 1 - Fair Values of Derivative Instruments (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Derivatives, Fair Value    
Asset Derivatives $ 8,064 $ 742
Liability Derivatives (309) (11,608)
Designated as Hedging Instruments    
Derivatives, Fair Value    
Asset Derivatives 8,059 0
Liability Derivatives (296) (10,100)
Designated as Hedging Instruments | Commodity contracts | Accrued liabilities    
Derivatives, Fair Value    
Asset Derivatives 28 0
Liability Derivatives (296) (112)
Designated as Hedging Instruments | Interest rate swaps | Other long-term assets, net    
Derivatives, Fair Value    
Asset Derivatives 8,031 0
Liability Derivatives 0 0
Designated as Hedging Instruments | Interest rate swaps | Accrued liabilities    
Derivatives, Fair Value    
Asset Derivatives 0 0
Liability Derivatives 0 (5,394)
Designated as Hedging Instruments | Interest rate swaps | Other long-term liabilities    
Derivatives, Fair Value    
Asset Derivatives 0 0
Liability Derivatives 0 (4,594)
Not Designated as Hedging Instruments | Commodity contracts | Accrued liabilities    
Derivatives, Fair Value    
Asset Derivatives 5 742
Liability Derivatives $ (13) $ (1,508)