RELATED PARTY TRANSACTIONS (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2019 USD ($) DTH contract Bcf	Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($)
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement	$ 1,524	$ 2,185
Demand fees payable	$ 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	1,494	1,473
Demand fees payable	775		775
NJRES to Steckman Ridge Affiliate
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement	30	$ 712
Demand fees payable	$ 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
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