REVENUE - DISAGGREGATED REVENUE - TYPE (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1,351,305	$ 1,229,949	$ 1,111,520
Revenues out of scope	685,107	566,590	851,474
Total operating revenues	2,036,412	1,796,539	1,962,994
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	869,857	717,785	692,422
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	361,716	416,965	332,729
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	110,042	86,600	77,722
Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,690	8,599	8,647
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	1,973,826	1,734,162	1,905,561
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0	0
Total operating revenues	62,586	62,377	57,433
Corporate, Non-Segment | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	62,396	62,219	57,091
Corporate, Non-Segment | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	190	158	342
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	1,089,879	860,532	844,043
Revenues out of scope	211,617	157,950	167,241
Total operating revenues	1,301,496	1,018,482	1,011,284
NJNG | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	805,351	641,606	621,663
NJNG | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	164,796	123,727	136,011
NJNG | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	110,042	86,600	77,722
NJNG | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,690	8,599	8,647
CEV | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	44,815	48,024	44,369
Revenues out of scope	67,686	82,539	79,762
Total operating revenues	112,501	130,563	124,131
CEV | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,110	13,960	13,668
CEV | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	42,705	34,064	30,701
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	19,700	137,200	48,500
ES | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	47,653	164,165	76,975
Revenues out of scope	405,804	326,101	604,471
Total operating revenues	453,457	490,266	681,446
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	47,653	164,165	76,975
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	106,372	94,851	88,700
Revenues out of scope	0	0	0
Total operating revenues	106,372	94,851	88,700
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	106,372	94,851	88,700
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