FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - LEVEL THREE INPUTS (Details) - Forward Contracts - Fair Value, Inputs, Level 3 $ in Thousands	Mar. 31, 2016 USD ($) $ / decatherm	Dec. 31, 2015 USD ($) $ / decatherm
Minimum | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	1.03	(0.77)
Minimum | Electricity | On-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	8.47%	8.47%
Minimum | Electricity | Off-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	0.00%	0.00%
Maximum | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	8.92	10.00
Maximum | Electricity | On-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	100.00%	100.00%
Maximum | Electricity | Off-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	91.53%	91.53%
Weighted Average | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	1.93	(2.15)
Weighted Average | Electricity | On-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	56.83%	56.20%
Weighted Average | Electricity | Off-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	43.17%	43.80%
Discounted Cash Flow | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets	$ 27,715	$ 29,459
Liabilities	15,874	31,733
Discounted Cash Flow | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets	26,458	29,136
Liabilities	$ 25,058	$ 27,494