RELATED PARTY TRANSACTIONS (Details) $ in Thousands			3 Months Ended
	Apr. 01, 2020 USD ($) Bcf	Apr. 01, 2010	Dec. 31, 2020 USD ($) DTH lease Bcf	Dec. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement			$ 1,734	$ 1,524
Demand fees payable			$ 865		$ 791
Number of asset management agreements | lease			3
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			$ 1,568	1,494
Demand fees payable			775		775
NJRES to Steckman Ridge Affiliate
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement			166	$ 30
Demand fees payable			$ 90		$ 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
NJNG to NJRES Affilate [Member]
Related Party Transaction [Line Items]
Asset management agreement, period		5 years