DERIVATIVE INSTRUMENTS (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2015 $ / MWh	Dec. 31, 2015 USD ($)
Derivative [Line Items]
Gain (loss) on derivative, net	$ (2,600)	$ 5,276
Not Designated as Hedging Instrument | Power Contract | Derivative loss
Derivative [Line Items]
Gain (loss) on derivative, net	(2,600)	$ 5,276
Not Designated as Hedging Instrument | Power Contract | Other current liabilities
Derivative [Line Items]
Derivative Liability	15,934			$ 13,679
Not Designated as Hedging Instrument | Power Contract | Other liabilities
Derivative [Line Items]
Derivative Liability	$ 23,834			$ 23,656
Minimum | Power Contract
Derivative [Line Items]
Contracted power price notional amount | $ / MWh			41.05
Maximum | 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			43.51