REVENUE - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 737,154	$ 519,083	$ 2,350,569	$ 1,678,048
Gas
Disaggregation of Revenue [Line Items]
Revenue	727,611	507,114	2,326,617	1,649,258
Electric
Disaggregation of Revenue [Line Items]
Revenue		2,807	21	6,244
Solar
Disaggregation of Revenue [Line Items]
Revenue	1,158	1,961	4,195	4,776
Fuel Cells
Disaggregation of Revenue [Line Items]
Revenue	6,180	5,063	13,283	12,167
Landfills
Disaggregation of Revenue [Line Items]
Revenue		328		1,037
Other
Disaggregation of Revenue [Line Items]
Revenue	2,205	1,810	6,453	4,566
Residential
Disaggregation of Revenue [Line Items]
Revenue	55,738	52,556	479,451	408,433
Commercial & Industrial
Disaggregation of Revenue [Line Items]
Revenue	674,431	461,657	1,848,653	1,256,644
OSS & Capacity Release
Disaggregation of Revenue [Line Items]
Revenue	4,742	2,504	14,166	7,053
Other
Disaggregation of Revenue [Line Items]
Revenue	2,243	2,366	8,299	5,918
SJG Utility Operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	71,313	63,785	467,792	379,401
SJG Utility Operations | Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	71,313	63,785	467,792	379,401
SJG Utility Operations | Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0	0	0
SJG Utility Operations | Solar | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
SJG Utility Operations | Fuel Cells | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
SJG Utility Operations | Landfills | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0		0
SJG Utility Operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
SJG Utility Operations | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	36,727	33,075	306,124	250,697
SJG Utility Operations | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	29,397	27,538	143,934	119,565
SJG Utility Operations | OSS & Capacity Release | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	4,742	2,504	14,166	7,053
SJG Utility Operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	447	668	3,568	2,086
ETG Utility Operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	39,462	37,638	279,328	246,466
ETG Utility Operations | Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	39,462	37,638	279,328	246,466
ETG Utility Operations | Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0	0	0
ETG Utility Operations | Solar | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
ETG Utility Operations | Fuel Cells | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
ETG Utility Operations | Landfills | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0		0
ETG Utility Operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
ETG Utility Operations | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	18,481	18,993	171,765	156,254
ETG Utility Operations | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	20,789	18,269	106,880	89,464
ETG Utility Operations | OSS & Capacity Release | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
ETG Utility Operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	192	376	683	748
Wholesale Energy Operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	624,866	406,985	1,599,474	1,032,181
Wholesale Energy Operations | Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	624,866	406,985	1,599,474	1,032,181
Wholesale Energy Operations | Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0	0	0
Wholesale Energy Operations | Solar | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Wholesale Energy Operations | Fuel Cells | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Wholesale Energy Operations | Landfills | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0		0
Wholesale Energy Operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Wholesale Energy Operations | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0
Wholesale Energy Operations | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	624,866	406,985	1,599,474	1,032,181
Wholesale Energy Operations | OSS & Capacity Release | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Wholesale Energy Operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Retail Services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,919	4,836	5,631	11,360
Retail Services | Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Retail Services | Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		2,846	21	6,409
Retail Services | Solar | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Retail Services | Fuel Cells | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Retail Services | Landfills | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0		0
Retail Services | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,919	1,990	5,610	4,951
Retail Services | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	530	488	1,562	1,482
Retail Services | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	2,846	21	6,409
Retail Services | OSS & Capacity Release | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Retail Services | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,389	1,502	4,048	3,469
Renewables | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	7,409	7,352	18,321	17,980
Renewables | Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Renewables | Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0	0	0
Renewables | Solar | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,158	1,961	4,195	4,776
Renewables | Fuel Cells | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	6,180	5,063	13,283	12,167
Renewables | Landfills | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		328		1,037
Renewables | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	71	0	843	0
Renewables | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Renewables | Commercial & Industrial | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	7,409	7,352	18,321	17,980
Renewables | OSS & Capacity Release | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Renewables | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Corporate Services and Intersegment | Intersegment Sales
Disaggregation of Revenue [Line Items]
Revenue	(7,815)	(1,513)	(19,977)	(9,340)
Corporate Services and Intersegment | Gas | Intersegment Sales
Disaggregation of Revenue [Line Items]
Revenue	(8,030)	(1,294)	(19,977)	(8,790)
Corporate Services and Intersegment | Electric | Intersegment Sales
Disaggregation of Revenue [Line Items]
Revenue		(39)	0	(165)
Corporate Services and Intersegment | Solar | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Corporate Services and Intersegment | Fuel Cells | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Corporate Services and Intersegment | Landfills | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue		0		0
Corporate Services and Intersegment | Other | Intersegment Sales
Disaggregation of Revenue [Line Items]
Revenue	215	(180)	0	(385)
Corporate Services and Intersegment | Residential | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Corporate Services and Intersegment | Commercial & Industrial | Intersegment Sales
Disaggregation of Revenue [Line Items]
Revenue	(8,030)	(1,333)	(19,977)	(8,955)
Corporate Services and Intersegment | OSS & Capacity Release | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Corporate Services and Intersegment | Other | Intersegment Sales
Disaggregation of Revenue [Line Items]
Revenue	$ 215	$ (180)	$ 0	$ (385)