REVENUE - DISAGGREGATED REVENUE - PRODUCT (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1,111,520	$ 1,198,985	$ 852,105
Alternative revenue programs	27,257	11,259	(7,282)
Derivative instruments	834,387	1,695,829	1,311,364
Revenues out of scope	851,474	1,706,994	1,304,508
Total operating revenues	1,962,994	2,905,979	2,156,613
Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	845,392	951,626	694,635
Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	169,834	151,536	77,953
Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	35,210	33,932	33,250
Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	22,428	22,250	18,979
Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,636	5,487	4,571
Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31,733	38,317	25,270
ES
Disaggregation of Revenue [Line Items]
Total operating revenues	48,500	53,000
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	1,905,561	2,850,161	2,105,169
Operating Segments | NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	844,043	950,276	694,635
Alternative revenue programs	27,257	11,259	(7,282)
Derivative instruments	139,984	165,882	44,443
Revenues out of scope	167,241	177,141	37,161
Total operating revenues	1,011,284	1,127,417	731,796
Operating Segments | NJNG | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	845,392	951,626	694,635
Operating Segments | NJNG | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | NJNG | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | NJNG | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | NJNG | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | NJNG | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | CEV
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	44,369	43,804	29,841
Alternative revenue programs	0	0	0
Derivative instruments	79,762	84,476	65,434
Revenues out of scope	79,762	84,476	65,434
Total operating revenues	124,131	128,280	95,275
Operating Segments | CEV | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | CEV | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | CEV | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | CEV | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | CEV | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,636	5,487	4,571
Operating Segments | CEV | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31,733	38,317	25,270
Operating Segments | ES
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	76,975	83,801	26,933
Alternative revenue programs	0	0	0
Derivative instruments	614,641	1,445,471	1,201,487
Revenues out of scope	604,471	1,445,377	1,201,913
Total operating revenues	681,446	1,529,178	1,228,846
Operating Segments | ES | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | ES | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	76,975	83,801	26,933
Operating Segments | ES | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | ES | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | ES | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | ES | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | S&T
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	88,700	65,286	49,252
Alternative revenue programs	0	0	0
Derivative instruments	0	0	0
Revenues out of scope	0	0	0
Total operating revenues	88,700	65,286	49,252
Operating Segments | S&T | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | S&T | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	92,859	67,735	51,020
Operating Segments | S&T | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | S&T | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | S&T | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Operating Segments | S&T | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0	0
Total operating revenues	57,433	55,818	51,444
Corporate, Non-Segment | HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	57,433	55,818	51,444
Alternative revenue programs	0	0	0
Derivative instruments	0	0	0
Revenues out of scope	0	0	0
Total operating revenues	57,433	55,818	51,444
Corporate, Non-Segment | HSO | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Corporate, Non-Segment | HSO | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Corporate, Non-Segment | HSO | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	35,210	33,932	33,250
Corporate, Non-Segment | HSO | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	22,428	22,250	18,979
Corporate, Non-Segment | HSO | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Corporate, Non-Segment | HSO | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(5,713)	(4,163)	(2,553)
Revenues out of scope	(10,170)	(94)	426
Eliminations | NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(1,349)	(1,350)	0
Revenues out of scope	0	0	0
Eliminations | CEV
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Revenues out of scope	0	0	0
Eliminations | ES
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Revenues out of scope	(10,170)	(94)	426
Eliminations | S&T
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(4,159)	(2,449)	(1,768)
Revenues out of scope	0	0	0
Eliminations | HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(205)	(364)	(785)
Revenues out of scope	$ 0	$ 0	$ 0