REVENUE - DISAGGREGATED REVENUE - PRODUCT (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 257,985	$ 234,836	$ 1,340,234	$ 1,162,987
Alternative revenue programs	5,032	48	(45,523)	(25,487)
Derivative instruments	86,163	64,062	598,724	562,834
Revenues out of scope	91,195	64,110	553,201	537,347
Total operating revenues	349,180	298,946	1,893,435	1,700,334
Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	172,004	168,140	1,121,684	973,993
Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	49,412	38,936	133,257	114,708
Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,760	9,381	28,743	27,883
Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,998	6,796	19,979	19,206
Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,469	4,964	15,586	10,726
Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,555	6,887	21,673	17,680
ES
Disaggregation of Revenue [Line Items]
Total operating revenues	4,900	4,900	14,800	14,800
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	331,427	282,799	1,844,718	1,653,532
Operating Segments \| NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	171,766	167,902	1,120,971	973,112
Alternative revenue programs	5,032	48	(45,523)	(25,487)
Derivative instruments	24,071	36,840	176,244	208,933
Revenues out of scope	29,103	36,888	130,721	183,446
Total operating revenues	200,869	204,790	1,251,692	1,156,558
Operating Segments \| NJNG \| Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	172,004	168,140	1,121,684	973,993
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	19,024	11,851	37,259	28,406
Alternative revenue programs	0	0	0	0
Derivative instruments	154	179	23,611	17,997
Revenues out of scope	154	179	23,611	17,997
Total operating revenues	19,178	12,030	60,870	46,403
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	8,469	4,964	15,586	10,726
Operating Segments \| CEV \| Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,555	6,887	21,673	17,680
Operating Segments \| ES
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,024	11,807	44,355	35,644
Alternative revenue programs	0	0	0	0
Derivative instruments	61,938	27,043	398,869	335,904
Revenues out of scope	61,938	27,043	398,869	335,904
Total operating revenues	79,962	38,850	443,224	371,548
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	18,024	11,807	44,355	35,644
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	31,418	27,129	88,932	79,023
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	31,418	27,129	88,932	79,023
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	31,388	27,129	88,902	79,064
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	17,753	16,147	48,717	46,802
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	17,753	16,147	48,717	46,802
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	9,760	9,381	28,743	27,883
HSO \| HSO \| Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,998	6,796	19,979	19,206
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	(213)	(268)	(688)	(1,209)
Eliminations \| NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(238)	(238)	(713)	(881)
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	30	0	30	(41)
Eliminations \| HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ (5)	$ (30)	$ (5)	$ (287)

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