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DERIVATIVES AND RISK MANAGEMENT ACTIVITIES Table 1 - Fair Values of Derivative Instruments (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Derivatives, Fair Value    
Asset Derivatives $ 742 $ 10,851
Liability Derivatives (11,608) (17,066)
Designated as Hedging Instrument    
Derivatives, Fair Value    
Asset Derivatives 0 1,458
Liability Derivatives (10,100) (6,198)
Designated as Hedging Instrument | Commodity contracts | Accrued liabilities    
Derivatives, Fair Value    
Asset Derivatives 0 144
Liability Derivatives (112) (3,566)
Designated as Hedging Instrument | Interest rate swaps | Other long-term assets, net    
Derivatives, Fair Value    
Asset Derivatives 0 1,314
Liability Derivatives 0 0
Designated as Hedging Instrument | Interest rate swaps | Accrued liabilities    
Derivatives, Fair Value    
Asset Derivatives 0 0
Liability Derivatives (5,394) 0
Designated as Hedging Instrument | Interest rate swaps | Other long-term liabilities    
Derivatives, Fair Value    
Asset Derivatives 0 0
Liability Derivatives (4,594) (2,632)
Not Designated as Hedging Instrument    
Derivatives, Fair Value    
Asset Derivatives 742 9,393
Liability Derivatives (1,508) (10,868)
Not Designated as Hedging Instrument | Commodity contracts | Other current assets    
Derivatives, Fair Value    
Asset Derivatives 0 265
Liability Derivatives 0 (110)
Not Designated as Hedging Instrument | Commodity contracts | Accrued liabilities    
Derivatives, Fair Value    
Asset Derivatives 742 9,128
Liability Derivatives $ (1,508) $ (10,758)