DEBT - CREDIT FACILITIES AND SHORT-TERM DEBT (Details) - USD ($)	3 Months Ended
	Dec. 31, 2025	Sep. 30, 2025
Letter of Credit | NJR
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	$ 21,500,000	$ 21,400,000
Letter of Credit | NJNG
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	$ 700,000	700,000
Revolving Credit Facility | NJR
Line of Credit Facility [Line Items]
Commitment fee percentage	0.10%
Revolving Credit Facility | NJNG
Line of Credit Facility [Line Items]
Commitment fee percentage	0.075%
Revolving Credit Facility | Committed Credit Facilities Due August 2029 | NJR
Line of Credit Facility [Line Items]
Total borrowing capacity	$ 575,000,000	575,000,000
Loans outstanding	$ 228,700,000	$ 152,600,000
Weighted average interest rate	4.99%	5.38%
Remaining borrowing capacity	$ 324,776,000	$ 401,018,000
Revolving Credit Facility | Committed Credit Facilities Due August 2029 | NJNG
Line of Credit Facility [Line Items]
Total borrowing capacity	250,000,000	250,000,000
Loans outstanding	$ 140,300,000	$ 43,000,000
Weighted average interest rate	3.93%	4.30%
Remaining borrowing capacity	$ 108,969,000	$ 206,269,000