FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) $ / decatherm	Dec. 31, 2015 USD ($) $ / decatherm
Liabilities
Net derivative assets (liabilities) transferred	$ 4,100	$ 7,400
Changes in significant unobservable inputs [Roll forward]
Balance at beginning of period	(632)	(5,608)
Other changes in fair value from continuing and new contracts, net	5,657	(5,069)
Transfers in to/(out of) of Level 3	4,116	7,402
Settlements	(106)	2,643
Balance at end of period	$ 9,035	$ (632)
Level 3 | Forward Contract | Minimum
Liabilities
Forward price (in USD per dt) | $ / decatherm	1.03	(0.77)
Level 3 | Forward Contract | Maximum
Liabilities
Forward price (in USD per dt) | $ / decatherm	11.33	10.00
Level 3 | Forward Contract | Weighted Average
Liabilities
Forward price (in USD per dt) | $ / decatherm	2.71	2.15
Level 3 | Forward Contract | Natural Gas
Liabilities
Assets	$ 23,301	$ 29,459
Liabilities	18,109	31,733
Level 3 | Forward Contract | Electric
Liabilities
Assets	11,784	29,136
Liabilities	$ 7,941	$ 27,494
Level 3 | Forward Contract | Electric | Minimum | On-peak
Liabilities
Fixed electric load profile	21.43%	8.47%
Level 3 | Forward Contract | Electric | Minimum | Off-peak
Liabilities
Fixed electric load profile	0.00%	0.00%
Level 3 | Forward Contract | Electric | Maximum | On-peak
Liabilities
Fixed electric load profile	100.00%	100.00%
Level 3 | Forward Contract | Electric | Maximum | Off-peak
Liabilities
Fixed electric load profile	78.57%	91.53%
Level 3 | Forward Contract | Electric | Weighted Average | On-peak
Liabilities
Fixed electric load profile	55.14%	56.20%
Level 3 | Forward Contract | Electric | Weighted Average | Off-peak
Liabilities
Fixed electric load profile	44.86%	43.80%
Measurement at fair value on recurring basis
Assets
Available-for-Sale Securities	$ 32	$ 14,810
Derivatives - Energy Related Assets	80,893	99,331
Assets	80,925	114,141
Liabilities
Derivatives - Energy Related Liabilities	64,622	112,405
Derivatives - Other	10,030	10,943
Liabilities	74,652	123,348
Measurement at fair value on recurring basis | Level 1
Assets
Available-for-Sale Securities	32	2,925
Derivatives - Energy Related Assets	33,994	16,006
Assets	34,026	18,931
Liabilities
Derivatives - Energy Related Liabilities	16,502	42,170
Derivatives - Other	0	0
Liabilities	16,502	42,170
Measurement at fair value on recurring basis | Level 2
Assets
Available-for-Sale Securities	0	11,885
Derivatives - Energy Related Assets	11,814	24,730
Assets	11,814	36,615
Liabilities
Derivatives - Energy Related Liabilities	22,070	11,008
Derivatives - Other	10,030	10,943
Liabilities	32,100	21,951
Measurement at fair value on recurring basis | Level 3
Assets
Available-for-Sale Securities	0	0
Derivatives - Energy Related Assets	35,085	58,595
Assets	35,085	58,595
Liabilities
Derivatives - Energy Related Liabilities	26,050	59,227
Derivatives - Other	0	0
Liabilities	$ 26,050	$ 59,227