REVENUE - DISAGGREGATED REVENUE - TYPE (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
Revenues out of scope	851,474	1,706,994	1,304,508
Total operating revenues	1,962,994	2,905,979	2,156,613
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	692,422	654,886	549,026
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	332,729	446,471	219,981
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	77,722	92,531	79,256
Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,647	5,097	3,842
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	1,905,561	2,850,161	2,105,169
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 | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	57,091	55,629	50,689
Corporate, Non-Segment | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	342	189	755
Corporate, Non-Segment | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
Corporate, Non-Segment | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
NJNG | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	844,043	950,276	694,635
Revenues out of scope	167,241	177,141	37,161
Total operating revenues	1,011,284	1,127,417	731,796
NJNG | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	621,663	586,678	487,018
NJNG | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	136,011	265,970	124,519
NJNG | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	77,722	92,531	79,256
NJNG | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,647	5,097	3,842
CEV | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	44,369	43,804	29,841
Revenues out of scope	79,762	84,476	65,434
Total operating revenues	124,131	128,280	95,275
CEV | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	13,668	12,579	11,319
CEV | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	30,701	31,225	18,522
CEV | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
CEV | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
ES
Disaggregation of Revenue [Line Items]
Total operating revenues	48,500	53,000
ES | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	76,975	83,801	26,933
Revenues out of scope	604,471	1,445,377	1,201,913
Total operating revenues	681,446	1,529,178	1,228,846
ES | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
ES | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	76,975	83,801	26,933
ES | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
ES | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
S&T | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	88,700	65,286	49,252
Revenues out of scope	0	0	0
Total operating revenues	88,700	65,286	49,252
S&T | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0
S&T | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	88,700	65,286	49,252
S&T | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	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