DERIVATIVE INSTRUMENTS (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) $ / MWh	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Derivative [Line Items]
Gain (loss) on derivative, net	$ (5,442)	$ (5,815)	$ (2,164)	$ (6,717)
Not Designated as Hedging Instrument | Power Contract | Derivative loss
Derivative [Line Items]
Gain (loss) on derivative, net	(5,442)	$ (5,815)	(2,164)	$ (6,717)
Not Designated as Hedging Instrument | Power Contract | Other current liabilities
Derivative [Line Items]
Derivative Liability	15,121		15,121		$ 13,679
Not Designated as Hedging Instrument | Power Contract | Other liabilities
Derivative [Line Items]
Derivative Liability	$ 24,043		$ 24,043		$ 23,656
Minimum [Member] | Power Contract
Derivative [Line Items]
Contracted power price notional amount | $ / MWh			41.05
Maximum [Member] | Power Contract
Derivative [Line Items]
Contracted power price notional amount | $ / MWh			55.2
Weighted Average | Power Contract
Derivative [Line Items]
Contracted power price notional amount | $ / MWh			44.00