SEGMENTS OF BUSINESS (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) investment	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) category	Dec. 31, 2015 USD ($) investment	Dec. 31, 2014 USD ($)
Segment Reporting Information [Line Items]
Operating Revenues	$ 329,981	$ 219,082	$ 154,402	$ 333,035	$ 257,844	$ 141,062	$ 177,710	$ 382,952	$ 1,036,500	$ 959,568	$ 886,996
Operating Income (Loss)									189,276	156,894	127,603
Depreciation and Amortization									109,818	91,042	78,511
Interest Charges									31,449	31,622	29,560
Income Taxes	19,266	$ 2,807	$ (7,189)	$ 39,267	(1,006)	$ (10,968)	$ (3,279)	$ 16,613	54,151	1,360	4,449
Property Additions									269,689	361,994	339,469
Identifiable Assets	3,730,567				$ 3,471,933				3,730,567	3,471,933
Marina Energy LLC | Energenic
Segment Reporting Information [Line Items]
Property, Plant and Equipment obtained through acquisition									$ 5,600	$ 40,900
Number of acquired projects (in investments) | investment					8					8
Energy Group and Energy Services
Segment Reporting Information [Line Items]
Number of Operating Segments | category									2
Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues									$ 1,094,093	$ 1,006,642	926,518
Interest Charges									42,304	40,523	36,036
Operating Segments | Gas Utility Operations
Segment Reporting Information [Line Items]
Operating Revenues									461,055	534,290	501,875
Operating Income (Loss)									122,455	119,585	113,690
Depreciation and Amortization									63,901	58,668	52,155
Interest Charges									17,875	19,906	17,872
Income Taxes									39,366	36,945	34,895
Property Additions									228,275	218,260	201,737
Identifiable Assets	2,551,923				$ 2,281,576				2,551,923	2,281,576
Operating Segments | Energy Group
Segment Reporting Information [Line Items]
Operating Revenues									495,618	366,345	327,822
Operating Income (Loss)									53,354	32,848	9,506
Depreciation and Amortization									821	596	251
Interest Charges									350	626	638
Income Taxes									20,862	13,858	5,419
Property Additions									1,649	2,435	1,439
Identifiable Assets	327,028				342,299				327,028	342,299
Operating Segments | Energy Group | Wholesale Energy Operations
Segment Reporting Information [Line Items]
Operating Revenues									220,707	129,098	77,048
Operating Income (Loss)									41,667	35,024	9,493
Depreciation and Amortization									484	435	168
Interest Charges									0	441	371
Income Taxes									15,882	14,410	4,822
Property Additions									7	382	18
Identifiable Assets	233,019				231,660				233,019	231,660
Operating Segments | Energy Group | Retail Gas and Other Operations
Segment Reporting Information [Line Items]
Operating Revenues									92,371	87,198	127,001
Operating Income (Loss)									4,680	(3,218)	479
Depreciation and Amortization									337	161	83
Interest Charges									350	185	267
Income Taxes									2,118	(978)	787
Property Additions									1,642	2,053	1,421
Identifiable Assets	52,729				55,111				52,729	55,111
Operating Segments | Energy Group | Retail Electric Operations
Segment Reporting Information [Line Items]
Operating Revenues									182,540	150,049	123,773
Operating Income (Loss)									7,007	1,042	(466)
Income Taxes									2,862	426	(190)
Identifiable Assets	41,280				55,528				41,280	55,528
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Operating Revenues									102,273	74,851	66,647
Operating Income (Loss)									13,883	2,495	2,922
Depreciation and Amortization									43,696	30,558	25,289
Income Taxes									(6,121)	(49,039)	(36,181)
Property Additions									38,624	139,397	132,298
Identifiable Assets	770,589				795,116				770,589	795,116
Operating Segments | Energy Services | On-Site Energy Production
Segment Reporting Information [Line Items]
Operating Revenues									94,375	63,665	56,129
Operating Income (Loss)									13,301	2,027	2,560
Depreciation and Amortization									43,395	30,242	25,020
Interest Charges									11,961	8,169	8,723
Income Taxes									(6,353)	(49,225)	(36,404)
Property Additions									38,193	139,018	132,214
Identifiable Assets	767,710				790,231				767,710	790,231
Operating Segments | Energy Services | Appliance Service Operations
Segment Reporting Information [Line Items]
Operating Revenues									7,898	11,186	10,518
Operating Income (Loss)									582	468	362
Depreciation and Amortization									301	316	269
Income Taxes									232	186	223
Property Additions									431	379	84
Identifiable Assets	2,879				4,885				2,879	4,885
Operating Segments | Corporate & Services
Segment Reporting Information [Line Items]
Operating Revenues									35,147	31,156	30,174
Operating Income (Loss)									(416)	1,966	1,485
Depreciation and Amortization									1,400	1,220	816
Interest Charges									12,118	11,822	8,803
Income Taxes									44	(404)	316
Property Additions									1,141	1,902	3,995
Identifiable Assets	649,795				652,325				649,795	652,325
Intersegment
Segment Reporting Information [Line Items]
Operating Revenues									(57,593)	(47,074)	(39,522)
Interest Charges									(10,855)	(8,901)	$ (6,476)
Identifiable Assets	(570,524)				(600,928)				(570,524)	(600,928)
Discontinued Operations
Segment Reporting Information [Line Items]
Identifiable Assets	$ 1,756				$ 1,545				$ 1,756	$ 1,545