REVENUE - DISAGGREGATED REVENUE - PRODUCT (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 641,350	$ 569,199	$ 1,082,249	$ 928,152
Alternative revenue programs	(24,299)	(20,145)	(50,555)	(25,536)
Derivative instruments	322,350	363,973	512,561	498,772
Revenues out of scope	298,051	343,828	462,006	473,236
Total operating revenues	939,401	913,027	1,544,255	1,401,388
Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	574,822	509,451	949,680	805,853
Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	42,925	37,197	83,845	75,772
Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,528	9,270	18,983	18,502
Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,430	5,848	11,981	12,410
Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,380	2,866	7,117	5,762
Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,503	4,967	11,118	10,793
ES
Disaggregation of Revenue [Line Items]
Total operating revenues	4,900	4,900	9,900	9,900
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	924,443	898,004	1,513,291	1,370,732
Operating Segments \| NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	574,584	509,145	949,205	805,210
Alternative revenue programs	(24,299)	(20,145)	(50,555)	(25,536)
Derivative instruments	90,637	129,339	152,173	172,093
Revenues out of scope	66,338	109,194	101,618	146,557
Total operating revenues	640,922	618,339	1,050,823	951,767
Operating Segments \| NJNG \| Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	574,822	509,451	949,680	805,853
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	8,883	7,833	18,235	16,555
Alternative revenue programs	0	0	0	0
Derivative instruments	1,049	134	23,457	17,818
Revenues out of scope	1,049	134	23,457	17,818
Total operating revenues	9,932	7,967	41,692	34,373
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	3,380	2,866	7,117	5,762
Operating Segments \| CEV \| Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,503	4,967	11,118	10,793
Operating Segments \| ES
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	13,491	11,890	26,331	23,837
Alternative revenue programs	0	0	0	0
Derivative instruments	230,664	234,500	336,931	308,861
Revenues out of scope	230,664	234,500	336,931	308,861
Total operating revenues	244,155	246,390	363,262	332,698
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	13,491	11,890	26,331	23,837
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	29,434	25,308	57,514	51,894
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	29,434	25,308	57,514	51,894
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	29,434	25,307	57,514	51,935
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
HSO \| HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,958	15,023	30,964	30,656
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	14,958	15,023	30,964	30,656
HSO \| HSO \| Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
HSO \| HSO \| Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
HSO \| HSO \| Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,528	9,270	18,983	18,502
HSO \| HSO \| Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,430	5,848	11,981	12,410
HSO \| HSO \| Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
HSO \| 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	(238)	(400)	(475)	(940)
Eliminations \| NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(238)	(306)	(475)	(643)
Eliminations \| CEV
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Eliminations \| ES
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Eliminations \| S&T
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	1	0	(41)
Eliminations \| HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ (95)	$ 0	$ (256)

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