DEBT - CREDIT FACILITIES AND SHORT-TERM DEBT (Details) - USD ($)	12 Months Ended
	Sep. 30, 2023	Feb. 07, 2023	Sep. 30, 2022	Aug. 30, 2022
NJR | Letters of Credit on Behalf of NJRES
Short-term Debt [Line Items]
Letters of credit outstanding, amount	$ 5,700,000		$ 9,700,000
NJR | Revolving Credit Facility
Short-term Debt [Line Items]
Commitment fee percentage	0.10%
NJNG | Letter of Credit
Short-term Debt [Line Items]
Letters of credit outstanding, amount	$ 700,000		700,000
NJNG | Revolving Credit Facility
Short-term Debt [Line Items]
Commitment fee percentage	0.075%
Revolving Credit Facility | NJR | Committed Credit Facilities Due September 2027
Short-term Debt [Line Items]
Total borrowing capacity	$ 650,000,000		650,000,000	$ 650,000,000
Loans outstanding	$ 217,300,000		$ 200,150,000
Weighted average interest rate	6.53%		3.97%
Remaining borrowing capacity	$ 426,967,000		$ 440,177,000
Revolving Credit Facility | NJNG | Committed Credit Facilities Due September 2027
Short-term Debt [Line Items]
Total borrowing capacity	250,000,000		250,000,000	$ 250,000,000
Loans outstanding	$ 34,800,000		$ 73,800,000
Weighted average interest rate	5.48%		3.34%
Remaining borrowing capacity	$ 214,469,000		$ 175,469,000
Term Loan | NJR | Committed Credit Facilities Due February 2023
Short-term Debt [Line Items]
Total borrowing capacity		$ 150,000,000	150,000,000
Loans outstanding			$ 150,000,000
Weighted average interest rate			3.81%
Remaining borrowing capacity			$ 0