DERIVATIVE INSTRUMENTS (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Not Designated as Hedging Instrument | Foreign Exchange Forward
Derivative [Line Items]
Number of foreign currency exchange forward contracts	2
Notional amount	$ 348,300,000
Not Designated as Hedging Instrument | Foreign Exchange Forward | Gain (loss) on foreign exchange
Derivative [Line Items]
Gain (loss) on derivative, net	0	(6,790,000)
Not Designated as Hedging Instrument | Power Contract | Derivative gain
Derivative [Line Items]
Gain (loss) on derivative, net	5,276,000	0
Not Designated as Hedging Instrument | Power Contract | Other current liabilities
Derivative [Line Items]
Derivative Liability	6,546,000		8,265,000
Not Designated as Hedging Instrument | Power Contract | Other liabilities
Derivative [Line Items]
Derivative Liability	$ 21,666,000		$ 21,103,000
Minimum | Power Contract
Derivative [Line Items]
Contracted power price notional amount	41.05
Maximum | Power Contract
Derivative [Line Items]
Contracted power price notional amount	56.33
Weighted Average | Power Contract
Derivative [Line Items]
Contracted power price notional amount	43.39