REVENUE - DISAGGREGATED REVENUE - PRODUCT (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 209,892	$ 199,315	$ 964,255	$ 948,299
Alternative revenue programs	(1,033)	5,211	3,812	29,016
Derivative instruments	66,777	60,179	427,817	663,544
Revenues out of scope	65,744	64,760	436,504	683,370
Total operating revenues	275,636	264,075	1,400,759	1,631,669
Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	138,804	134,253	767,698	749,618
Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	40,679	38,222	119,996	130,631
Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,062	8,842	27,073	26,242
Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,294	6,113	19,022	16,427
Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,872	4,720	10,194	8,007
Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,575	8,274	22,842	22,062
ES
Disaggregation of Revenue [Line Items]
Total operating revenues	9,500	9,500	28,500	39,000
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	259,337	249,126	1,354,874	1,589,202
Operating Segments | NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	138,467	133,916	766,686	748,606
Alternative revenue programs	(1,033)	5,211	3,812	29,016
Derivative instruments	20,339	5,844	143,231	125,258
Revenues out of scope	19,306	11,055	147,043	154,274
Total operating revenues	157,773	144,971	913,729	902,880
Operating Segments | NJNG | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	138,804	134,253	767,698	749,618
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	14,447	12,994	33,036	30,069
Alternative revenue programs	0	0	0	0
Derivative instruments	201	184	26,232	10,307
Revenues out of scope	201	184	26,232	10,307
Total operating revenues	14,648	13,178	59,268	40,376
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	4,872	4,720	10,194	8,007
Operating Segments | CEV | Electricity sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,575	8,274	22,842	22,062
Operating Segments | ES
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,204	16,021	48,617	60,705
Alternative revenue programs	0	0	0	0
Derivative instruments	46,237	54,151	258,354	527,979
Revenues out of scope	46,237	53,521	263,229	518,789
Total operating revenues	62,441	69,542	311,846	579,494
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	16,204	16,021	48,617	60,705
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	24,475	21,435	70,031	66,452
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	24,475	21,435	70,031	66,452
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	24,475	22,201	71,379	69,926
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
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0	0	0
Total operating revenues	16,299	14,949	45,885	42,467
Corporate, Non-Segment | HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,299	14,949	45,885	42,467
Alternative revenue programs	0	0	0	0
Derivative instruments	0	0	0	0
Revenues out of scope	0	0	0	0
Total operating revenues	16,299	14,949	45,885	42,467
Corporate, Non-Segment | HSO | Natural gas utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate, Non-Segment | HSO | Natural gas services
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate, Non-Segment | HSO | Service contracts
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,062	8,842	27,073	26,242
Corporate, Non-Segment | HSO | Installations and maintenance
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7,294	6,113	19,022	16,427
Corporate, Non-Segment | HSO | Renewable energy certificates
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate, Non-Segment | 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	(394)	(1,109)	(2,570)	(4,688)
Revenues out of scope		(630)	4,875	(9,190)
Total operating revenues		(1,739)		(13,878)
Eliminations | NJNG
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(337)	(337)	(1,012)	(1,012)
Revenues out of scope		0	0	0
Eliminations | CEV
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	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	0
Revenues out of scope		(630)	4,875	(9,190)
Eliminations | S&T
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	(766)	(1,348)	(3,474)
Revenues out of scope		0	0	0
Eliminations | HSO
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ (57)	(6)	(210)	(202)
Revenues out of scope		$ 0	$ 0	$ 0