RELATED PARTY TRANSACTIONS (Details) $ in Thousands				3 Months Ended		6 Months Ended
	Feb. 19, 2021 DTH	Apr. 01, 2020 USD ($) Bcf	Apr. 01, 2010	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2021 USD ($) DTH lease Bcf	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement				$ 1,731	$ 1,506	$ 3,464	$ 3,030
Demand fees payable				853		$ 853		$ 791
Number of asset management agreements | lease						3
NJNG to NJRES Affiliate
Related Party Transaction [Line Items]
Asset management agreement, period			5 years
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				1,505	1,477	$ 3,073	2,971
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				226	$ 29	391	$ 59
Demand fees payable				$ 78		$ 78		$ 16
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
Storage capacity park and loan agreement | DTH	330,000