Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS (Derivative Instruments in Financial Position) (Details)

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DERIVATIVE INSTRUMENTS (Derivative Instruments in Financial Position) (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
General Discussion of Derivative Instruments and Hedging Activities [Abstract]    
Short-term derivative instruments - asset $ 19,809 $ 78,847
Long-term derivative instruments - asset 3,530 8,685
Short-term derivative instruments - liability 62,601 32,534
Long-term derivative instruments - liability $ 15,101 $ 2,989