REVENUE - DISAGGREGATED REVENUE - PRODUCT (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 433,172	$ 384,433	$ 754,363	$ 748,984
Alternative revenue programs	7,382	27,270	4,845	23,805
Derivative instruments	213,617	232,501	361,040	603,365
Revenues out of scope	224,741	259,594	370,760	618,610
Total operating revenues	657,913	644,027	1,125,123	1,367,594
Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	371,019	327,198	628,894	615,365
Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	39,187	37,723	79,317	92,409
Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,071	8,739	18,011	17,400
Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,834	4,709	11,728	10,314
Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,672	2,085	5,322	3,287
Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,553	6,084	13,267	13,788
ES
Disaggregation of Revenue [Line Items]
Total operating revenues	9,500	9,500	19,000	29,500
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	643,161	630,762	1,095,537	1,340,076
Operating Segments | NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	370,681	326,860	628,219	614,690
Alternative revenue programs	7,382	27,270	4,845	23,805
Derivative instruments	84,800	46,370	122,892	119,414
Revenues out of scope	92,182	73,640	127,737	143,219
Total operating revenues	462,863	400,500	755,956	757,909
Operating Segments | NJNG | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	371,019	327,198	628,894	615,365
Operating Segments | NJNG | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | NJNG | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | NJNG | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | NJNG | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | NJNG | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | CEV
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,225	8,169	18,589	17,075
Alternative revenue programs	0	0	0	0
Derivative instruments	100	6,237	26,031	10,123
Revenues out of scope	100	6,237	26,031	10,123
Total operating revenues	9,325	14,406	44,620	27,198
Operating Segments | CEV | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | CEV | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | CEV | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | CEV | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | CEV | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,672	2,085	5,322	3,287
Operating Segments | CEV | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,553	6,084	13,267	13,788
Operating Segments | ES
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,145	16,836	32,413	44,684
Alternative revenue programs	0	0	0	0
Derivative instruments	128,717	179,894	212,117	473,828
Revenues out of scope	132,459	179,717	216,992	465,268
Total operating revenues	148,604	196,553	249,405	509,952
Operating Segments | ES | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | ES | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,145	16,836	32,413	44,684
Operating Segments | ES | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | ES | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | ES | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | ES | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | S&T
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	22,369	19,303	45,556	45,017
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	22,369	19,303	45,556	45,017
Operating Segments | S&T | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | S&T | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	23,042	20,887	46,904	47,725
Operating Segments | S&T | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | S&T | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | S&T | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Operating Segments | S&T | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0	0	0
Total operating revenues	14,752	13,265	29,586	27,518
Corporate, Non-Segment | HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,752	13,265	29,586	27,518
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	14,752	13,265	29,586	27,518
Corporate, Non-Segment | HSO | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate, Non-Segment | HSO | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate, Non-Segment | HSO | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,071	8,739	18,011	17,400
Corporate, Non-Segment | HSO | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,834	4,709	11,728	10,314
Corporate, Non-Segment | HSO | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate, Non-Segment | HSO | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(1,164)	(2,105)	(2,176)	(3,579)
Revenues out of scope	3,742	(177)	4,875	(8,560)
Total operating revenues		(2,282)		(12,139)
Eliminations | NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(338)	(338)	(675)	(675)
Revenues out of scope	0	0	0	0
Eliminations | CEV
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Revenues out of scope	0	0	0	0
Eliminations | ES
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Revenues out of scope	3,742	(177)	4,875	(8,560)
Eliminations | S&T
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(673)	(1,584)	(1,348)	(2,708)
Revenues out of scope	0	0	0	0
Eliminations | HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(153)	(183)	(153)	(196)
Revenues out of scope	$ 0	$ 0	$ 0	$ 0