FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES, LEVEL THREE INPUTS (Details) (Forward Contracts, Fair Value, Inputs, Level 3, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets	$ 19,557	$ 26,485
Liabilities	38,607	33,882
Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets	6,451	8,020
Liabilities	$ 4,712	$ 6,231
Minimum | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt)	(1.61)	(2.04)
Maximum | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt)	7.25	7.83
Weighted Average | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt)	(0.28)	(0.30)
On-Peak | Minimum | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	8.06%	8.06%
On-Peak | Maximum | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	100.00%	100.00%
On-Peak | Weighted Average | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	56.75%	55.97%
Off-Peak | Minimum | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	0.00%	0.00%
Off-Peak | Maximum | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	91.94%	91.94%
Off-Peak | Weighted Average | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	43.25%	44.03%