FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES, LEVEL THREE INPUTS (Details) (Forward Contracts [Member], Fair Value, Inputs, Level 3 [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Natural Gas [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets	$ 17,019	$ 4,340
Liabilities	28,069	4,986
Electricity [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets	7,194	6,590
Liabilities	$ 4,659	$ 3,182
Minimum [Member] | Natural Gas [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt)	(1.20)	(0.35)
Maximum [Member] | Natural Gas [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt)	3.58	2.92
Weighted Average [Member] | Natural Gas [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt)	(0.49)	(0.12)
On-Peak [Member] | Minimum [Member] | Electricity [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	19.72%	21.62%
On-Peak [Member] | Maximum [Member] | Electricity [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	100.00%	100.00%
On-Peak [Member] | Weighted Average [Member] | Electricity [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	60.44%	53.64%
Off-Peak [Member] | Minimum [Member] | Electricity [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	0.00%	0.00%
Off-Peak [Member] | Maximum [Member] | Electricity [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	80.28%	78.38%
Off-Peak [Member] | Weighted Average [Member] | Electricity [Member]
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	39.56%	46.36%