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DERIVATIVE AND HEDGING ACTIVITIES - Realized Unrealized (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Derivative and hedging activities    
Total net gain (loss) on derivative contracts $ (64,799) $ 5,903
Derivatives not designated as hedging contracts | Commodity contracts | Other Income Expense    
Derivative and hedging activities    
Unrealized gain (loss) on commodity contracts (68,169) 11,113,000
Realized gain (loss) on commodity contracts 3,370 (5,210,000)
Total net gain (loss) on derivative contracts $ (64,799) $ 5,903,000