RELATED PARTY TRANSACTIONS (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) DTH contract Bcf	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement	$ 1,518	$ 2,126	$ 4,548	$ 6,455
Demand fees payable	791		$ 791		$ 790
Number of asset management agreements | contract			4
NJNG to Steckman RIdge Affiliate
Related Party Transaction [Line Items]
Natural gas sold at cost under asset management agreement (in Bcf) | Bcf			3
Approximate annual demand fees under agreement			$ 9,300
Demand fees expense recognized pertaining to related party agreement	1,491	1,431	4,462	4,349
Demand fees payable	775		775		775
NJRES to Steckman Ridge Affiliate
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement	27	$ 695	86	$ 2,106
Demand fees payable	$ 16		$ 16		$ 15
NJNG to PennEast Affiliate
Related Party Transaction [Line Items]
Natural gas transportation capacity agreement, period			15 years
Transportation capacity under precedent agreement with PennEast (in bcf per day) | DTH			180,000
NJRES to PennEast Affiliate
Related Party Transaction [Line Items]
Natural gas transportation capacity agreement, period			5 years
Transportation capacity under precedent agreement with PennEast (in bcf per day) | DTH			50,000
NJN G to Adelphia Affiliate
Related Party Transaction [Line Items]
Transportation capacity under precedent agreement with PennEast (in bcf per day) | DTH			130,000
Leaf River Energy Center LLC
Related Party Transaction [Line Items]
Natural gas sold at cost under asset management agreement (in Bcf) | Bcf			3
Storage capacity agreement term			5 years