SEGMENTS OF BUSINESS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Operating Revenues	$ 197,558	$ 111,977	$ 121,913	$ 274,832	$ 198,540	$ 137,621	$ 160,477	$ 331,922	$ 706,280	$ 828,560	$ 925,067
Operating Income (Loss)									109,898	121,607	116,492
Depreciation and Amortization									55,089	47,759	44,694
Interest Charges									18,986	24,078	21,896
Income Taxes									11,479	22,502	28,811
Property Additions									269,525	199,975	163,963
Identifiable Assets	2,631,440				2,247,510				2,631,440	2,247,510
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenues									745,258	870,518	967,164
Interest Charges									21,950	27,246	22,881
Operating Segments [Member] | Gas Utility Operations [Member]
Segment Reporting Information [Line Items]
Operating Revenues									421,874	412,449	475,982
Operating Income (Loss)									101,762	102,663	90,700
Depreciation and Amortization									44,171	41,959	39,502
Interest Charges									12,427	18,922	17,641
Income Taxes									33,711	34,281	29,676
Property Additions									156,990	141,918	111,653
Identifiable Assets	1,786,459				1,615,723				1,786,459	1,615,723
Operating Segments [Member] | Wholesale Energy Operations [Member]
Segment Reporting Information [Line Items]
Operating Revenues									17,429	68,370	88,729
Operating Income (Loss)									(2,142)	16,225	6,154
Depreciation and Amortization									229	253	252
Interest Charges									229	54	94
Income Taxes									(907)	7,517	3,243
Property Additions									23	83	682
Identifiable Assets	204,358				178,863				204,358	178,863
Operating Segments [Member] | Retail Energy Operations [Member]
Segment Reporting Information [Line Items]
Operating Revenues									276,637	364,374	379,985
Operating Income (Loss)									9,558	2,948	18,611
Depreciation and Amortization									9,990	4,882	4,299
Interest Charges									5,075	5,622	4,070
Income Taxes									(21,849)	(19,550)	(4,430)
Property Additions									108,204	57,369	50,599
Identifiable Assets	608,060				430,697				608,060	430,697
Operating Segments [Member] | Retail Energy Operations [Member] | Retail Gas and Other Operations [Member]
Segment Reporting Information [Line Items]
Operating Revenues									80,486	100,977	114,536
Operating Income (Loss)									(1,204)	478	1,065
Depreciation and Amortization									78	33	35
Interest Charges									139	186	172
Income Taxes									(144)	511	678
Property Additions									177	22	31
Identifiable Assets	39,481				23,568				39,481	23,568
Operating Segments [Member] | Retail Energy Operations [Member] | Retail Electric Operations [Member]
Segment Reporting Information [Line Items]
Operating Revenues									144,197	206,422	207,576
Operating Income (Loss)									12,683	1,755	13,051
Income Taxes									5,181	717	5,353
Identifiable Assets	21,919				31,225				21,919	31,225
Operating Segments [Member] | Retail Energy Operations [Member] | On-site Energy Production [Member]
Segment Reporting Information [Line Items]
Operating Revenues									38,308	39,919	38,138
Operating Income (Loss)									(1,696)	2,254	4,063
Depreciation and Amortization									9,604	4,527	3,920
Interest Charges									4,936	5,436	3,898
Income Taxes									(26,811)	(22,258)	(10,635)
Property Additions									107,993	57,093	50,427
Identifiable Assets	543,416				369,307				543,416	369,307
Operating Segments [Member] | Retail Energy Operations [Member] | Appliance Service Operations [Member]
Segment Reporting Information [Line Items]
Operating Revenues									13,646	17,056	19,735
Operating Income (Loss)									(225)	(1,539)	432
Depreciation and Amortization									308	322	344
Income Taxes									(75)	1,480	174
Property Additions									34	254	141
Identifiable Assets	3,244				6,597				3,244	6,597
Operating Segments [Member] | Corporate and Services [Member]
Segment Reporting Information [Line Items]
Operating Revenues									29,318	25,325	22,468
Operating Income (Loss)									720	(229)	1,027
Depreciation and Amortization									699	665	641
Interest Charges									4,219	2,648	1,076
Income Taxes									524	254	322
Property Additions									4,308	605	1,029
Identifiable Assets	337,010				150,280				337,010	150,280
Segment, Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable Assets	78				224				78	224
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(38,978)	(41,958)	(42,097)
Interest Charges									(2,964)	(3,168)	(985)
Identifiable Assets	$ (304,525)				$ (128,277)				$ (304,525)	$ (128,277)