DEBT - CREDIT FACILITIES AND SHORT-TERM DEBT (Details) - USD ($)	3 Months Ended
	Dec. 31, 2022	Sep. 30, 2022
NJR | Letter of Credit on Behalf of NJRES
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	$ 19,700,000	$ 9,700,000
NJNG | Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	$ 731,000	731,000
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 September 2027 | NJR
Line of Credit Facility [Line Items]
Bank revolving credit facilities	$ 650,000,000	650,000,000
Amount outstanding at end of period	$ 202,650,000	$ 200,150,000
Weighted average interest rate at end of period	5.54%	3.97%
Amount available at end of period	$ 427,677,000	$ 440,177,000
Revolving Credit Facility | Committed Credit Facilities Due September 2027 | NJNG
Line of Credit Facility [Line Items]
Bank revolving credit facilities	250,000,000	250,000,000
Amount outstanding at end of period	$ 111,800,000	$ 73,800,000
Weighted average interest rate at end of period	4.60%	3.34%
Amount available at end of period	$ 137,469,000	$ 175,469,000
Term Loan | Committed Credit Facilities Due February 2023 | NJR
Line of Credit Facility [Line Items]
Bank revolving credit facilities	150,000,000	150,000,000
Amount outstanding at end of period	$ 150,000,000	$ 150,000,000
Weighted average interest rate at end of period	5.17%	3.81%
Amount available at end of period	$ 0	$ 0