LEASES - ADDITIONAL INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023	Jul. 31, 2021
Lessee, Lease, Description [Line Items]
ROU asset obtained in exchange for operating lease liability	$ 2,600	$ 300	$ 4,100	$ 400
Proceeds from sale leaseback transactions - natural gas meters			8,814	8,441
ROU asset obtained in exchange for finance lease liability	$ 0	$ 0	$ 0
Weighted average remaining lease term, operating lease	28 years 7 months 6 days		28 years 7 months 6 days		29 years 2 months 12 days
Operating lease, discount rate	3.60%		3.60%		3.50%
Weighted average remaining lease term, finance lease	3 years 4 months 24 days		3 years 4 months 24 days		3 years 3 months 18 days
Finance lease, discount rate	3.30%		3.30%		2.70%
NJNG
Lessee, Lease, Description [Line Items]
Proceeds from sale leaseback transactions - natural gas meters			$ 8,800	$ 8,400
Solar Property | Minimum
Lessee, Lease, Description [Line Items]
Term of contract	20 years		20 years
Renewal term	5 years		5 years
Solar Property | Maximum
Lessee, Lease, Description [Line Items]
Term of contract	50 years		50 years
Renewal term	20 years		20 years
Office Building
Lessee, Lease, Description [Line Items]
Term of contract						16 years
Office Building | Minimum
Lessee, Lease, Description [Line Items]
Term of contract	2 years		2 years
Office Building | Maximum
Lessee, Lease, Description [Line Items]
Term of contract	11 years		11 years
Meter License | Minimum
Lessee, Lease, Description [Line Items]
Term of contract	6 years		6 years
Meter License | Maximum
Lessee, Lease, Description [Line Items]
Term of contract	10 years		10 years
Equipment
Lessee, Lease, Description [Line Items]
Term of contract	9 years		9 years
Storage and Capacity
Lessee, Lease, Description [Line Items]
Term of contract	50 years		50 years