SEGMENTS OF BUSINESS (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) category	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Total Operating Revenues	$ 227,127	$ 219,082	$ 897,330	$ 706,519
Total Operating (Loss) Income	(55,255)	12,590	7,867	118,857
Total Depreciation and Amortization	30,084	27,798	89,316	81,260
Total Interest Charges	10,567	7,355	38,291	24,744
Total Income Taxes	(24,765)	2,807	(8,439)	34,885
Total Property Additions	61,121	63,477	201,574	172,107
Total Identifiable Assets	3,740,066		3,740,066		$ 3,730,567
Discontinued Operations
Segment Reporting Information [Line Items]
Total Identifiable Assets	1,769		$ 1,769		1,756
Energy Group and Energy Services
Segment Reporting Information [Line Items]
Number of operating categories | category			2
Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	242,039	233,306	$ 947,238	748,788
Total Interest Charges	14,934	10,072	50,104	32,867
Operating Segments | Gas Utility Operations
Segment Reporting Information [Line Items]
Total Operating Revenues	66,755	62,025	346,820	318,553
Total Operating (Loss) Income	(4,628)	(2,453)	84,174	83,251
Total Depreciation and Amortization	17,751	15,954	52,559	47,368
Total Interest Charges	6,437	4,058	18,392	13,397
Total Income Taxes	(3,688)	(2,007)	27,654	26,812
Total Property Additions	59,179	53,623	187,587	155,126
Total Identifiable Assets	2,736,775		2,736,775		2,551,923
Operating Segments | Energy Group
Segment Reporting Information [Line Items]
Total Operating Revenues	134,213	131,376	488,353	329,735
Total Operating (Loss) Income	(12,264)	6,717	(42,847)	22,165
Total Depreciation and Amortization	111	124	339	700
Total Interest Charges	(107)	86	3,235	328
Total Income Taxes	(4,647)	2,562	(17,383)	8,493
Total Property Additions	204	455	637	1,187
Total Identifiable Assets	221,523		221,523		327,028
Operating Segments | Energy Group | Wholesale Energy Operations
Segment Reporting Information [Line Items]
Total Operating Revenues	70,741	67,926	274,667	131,691
Total Operating (Loss) Income	(11,346)	8,014	(41,163)	15,109
Total Depreciation and Amortization	31	39	92	447
Total Interest Charges	(162)	0	3,031	32
Total Income Taxes	(4,281)	3,125	(16,984)	5,604
Total Property Additions	0	0	5	7
Total Identifiable Assets	153,933		153,933		233,019
Operating Segments | Energy Group | Retail Gas and Other Operations
Segment Reporting Information [Line Items]
Total Operating Revenues	18,156	11,865	76,793	63,903
Total Operating (Loss) Income	(574)	(2,520)	(3,801)	2,971
Total Depreciation and Amortization	80	85	247	253
Total Interest Charges	55	86	204	296
Total Income Taxes	(225)	(1,062)	(1,265)	1,220
Total Property Additions	204	455	632	1,180
Total Identifiable Assets	35,487		35,487		52,729
Operating Segments | Energy Group | Retail Electric Operations
Segment Reporting Information [Line Items]
Total Operating Revenues	45,316	51,585	136,893	134,141
Total Operating (Loss) Income	(344)	1,223	2,117	4,085
Total Income Taxes	(141)	499	866	1,669
Total Identifiable Assets	32,103		32,103		41,280
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Total Operating Revenues	31,494	32,846	79,879	76,148
Total Operating (Loss) Income	(38,743)	8,354	(35,614)	13,128
Total Depreciation and Amortization	11,774	11,347	35,151	32,336
Total Income Taxes	(16,490)	2,220	(19,321)	(530)
Total Property Additions	1,633	9,225	12,159	14,893
Total Identifiable Assets	663,807		663,807		770,589
Operating Segments | Energy Services | On-Site Energy Production
Segment Reporting Information [Line Items]
Total Operating Revenues	29,942	31,034	74,689	70,398
Total Operating (Loss) Income	(38,351)	8,077	(35,216)	12,549
Total Depreciation and Amortization	11,731	11,274	34,998	32,088
Total Interest Charges	3,549	3,032	13,240	9,936
Total Income Taxes	(16,270)	2,118	(19,120)	(784)
Total Property Additions	1,633	9,152	11,899	14,468
Total Identifiable Assets	662,087		662,087		767,710
Operating Segments | Energy Services | Appliance Service Operations
Segment Reporting Information [Line Items]
Total Operating Revenues	1,552	1,812	5,190	5,750
Total Operating (Loss) Income	(392)	277	(398)	579
Total Depreciation and Amortization	43	73	153	248
Total Income Taxes	(220)	102	(201)	254
Total Property Additions	0	73	260	425
Total Identifiable Assets	1,720		1,720		2,879
Corporate and Services
Segment Reporting Information [Line Items]
Total Operating Revenues	9,577	7,059	32,186	24,352
Total Operating (Loss) Income	380	(28)	2,154	313
Total Depreciation and Amortization	448	373	1,267	856
Total Interest Charges	5,055	2,896	15,237	9,206
Total Income Taxes	60	32	611	110
Total Property Additions	105	174	1,191	901
Total Identifiable Assets	781,238		781,238		649,795
Intersegment eliminations
Segment Reporting Information [Line Items]
Total Operating Revenues	(14,912)	(14,224)	(49,908)	(42,269)
Total Interest Charges	(4,367)	$ (2,717)	(11,813)	$ (8,123)
Total Identifiable Assets	$ (665,046)		$ (665,046)		$ (570,524)