DERIVATIVE INSTRUMENTS - FAIR VALUE OF ALL DERIVATIVE INSTRUMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	$ 4,127	$ 1,141
Fair value Derivative Liabilities	15,060	13,471
Commodity Contract
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	4,127	1,141
Fair value Derivative Liabilities	0	0
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	4,127	1,141
Fair value Derivative Liabilities	15,060	13,471
Not Designated as Hedging Instrument | Commodity Contract | Derivatives-Energy Related-Current
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	3,573	1,077
Fair value Derivative Liabilities	4,694	5,489
Not Designated as Hedging Instrument | Commodity Contract | Derivatives-Energy Related-NonCurrent
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	554	64
Fair value Derivative Liabilities	3	351
Not Designated as Hedging Instrument | Interest Rate Contract | Derivatives-Other Current
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	0	0
Fair value Derivative Liabilities	529	0
Not Designated as Hedging Instrument | Interest Rate Contract | Derivatives-Other Noncurrent
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	0
Fair value Derivative Liabilities	$ 9,834	$ 7,631