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DERIVATIVES AND RISK MANAGEMENT ACTIVITIES Table 3 - Impact of Derivatives on Earnings (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Derivative Instruments, Gain (Loss)      
Gain (loss) to be reclassified during next 12 months, forward starting interest rate swaps $ (5,100)    
Designated as Hedging Instrument | Fair Value Hedges | Commodity contracts | Cost of product sales      
Derivative Instruments, Gain (Loss)      
Gain (loss) recognized in income on derivative 806 $ (11,254) $ 21,589
Gain (loss) recognized in income on hedged item (656) 15,295 (18,047)
Gain (loss) recognized in income on derivative (ineffective portion) 150 4,041 3,542
Designated as Hedging Instrument | Cash Flow Hedges | Interest rate swaps | Other comprehensive income (loss)      
Derivative Instruments, Gain (Loss)      
Gain (loss) recognized in other comprehensive income on derivative (effective portion) (8,670) (2,621) 1,303
Designated as Hedging Instrument | Cash Flow Hedges | Interest rate swaps | Interest expense, net      
Derivative Instruments, Gain (Loss)      
Gain (loss) reclassified from AOCI into income (effective portion) (6,624) (8,331) (9,802)
Not Designated as Hedging Instrument | Commodity contracts | Cost of product sales      
Derivative Instruments, Gain (Loss)      
Gain (loss) recognized in income on derivative $ (668) $ 225 $ 2,208