REVENUE - DISAGGREGATED REVENUE - TYPE (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 569,199	$ 433,172	$ 928,152	$ 754,363
Revenues out of scope	343,828	224,741	473,236	370,760
Total operating revenues	913,027	657,913	1,401,388	1,125,123
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	407,080	305,737	648,553	519,549
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	118,570	94,940	205,609	176,163
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	42,408	30,680	69,733	55,115
Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,141	1,815	4,257	3,536
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	898,004	643,161	1,370,732	1,095,537
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Total operating revenues	15,023	14,752	30,656	29,586
NJNG | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	509,145	370,681	805,210	628,219
Revenues out of scope	109,194	92,182	146,557	127,737
Total operating revenues	618,339	462,863	951,767	755,956
NJNG | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	392,100	287,824	615,919	483,447
NJNG | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	73,496	50,362	115,301	86,121
NJNG | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	42,408	30,680	69,733	55,115
NJNG | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,141	1,815	4,257	3,536
CEV | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,833	9,225	16,555	18,589
Revenues out of scope	134	100	17,818	26,031
Total operating revenues	7,967	9,325	34,373	44,620
CEV | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	3,229	2,110	6,615
CEV | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,833	5,996	14,445	11,974
CEV | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
CEV | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
ES
Disaggregation of Revenue [Line Items]
Total operating revenues	4,900	9,500	9,900	19,000
ES | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,890	16,145	23,837	32,413
Revenues out of scope	234,500	132,459	308,861	216,992
Total operating revenues	246,390	148,604	332,698	249,405
ES | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
ES | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,890	16,145	23,837	32,413
ES | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
ES | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
S&T | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	25,308	22,369	51,894	45,556
Revenues out of scope	0	0	0	0
Total operating revenues	25,308	22,369	51,894	45,556
S&T | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
S&T | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	25,308	22,369	51,894	45,556
S&T | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
S&T | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
HSO | Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	15,023	14,752	30,656	29,586
Revenues out of scope	0	0	0	0
Total operating revenues	15,023	14,752	30,656	29,586
HSO | Corporate, Non-Segment | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,980	14,684	30,524	29,487
HSO | Corporate, Non-Segment | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	43	68	132	99
HSO | Corporate, Non-Segment | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
HSO | Corporate, Non-Segment | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0	$ 0	$ 0