FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES, LEVEL THREE INPUTS (Details) - Forward Contracts - Fair Value, Inputs, Level 3 $ in Thousands	Sep. 30, 2015 USD ($) $ / decatherm	Dec. 31, 2014 USD ($) $ / decatherm
Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets	$ 19,113	$ 26,485
Liabilities	35,812	33,882
Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets	21,219	8,020
Liabilities	$ 19,185	$ 6,231
Minimum | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	(0.95)	(2.04)
Maximum | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	9.83	7.83
Weighted Average | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	0.45	(0.30)
On-Peak | Minimum | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	8.47%	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	56.44%	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	91.53%	91.94%
Off-Peak | Weighted Average | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	43.56%	44.03%