RELATED PARTY TRANSACTIONS (Details) DTH in Thousands, $ in Thousands		12 Months Ended
	Apr. 01, 2010 USD ($) Bcf	Sep. 30, 2019 USD ($) DTH contract	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Related Party Transaction [Line Items]
Demand fees recognized pertaining to related party agreement		$ 7,948	$ 8,505	$ 8,340
Due to related parties		$ 790	1,150
Number of asset management agreements | contract		4
NJNG to NJRES Affiliate
Related Party Transaction [Line Items]
Asset management agreement, period	10 years
NJNG to Steckman RIdge Affiliate - National Gas Distribution
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 recognized pertaining to related party agreement		$ 5,814	5,730	5,590
Due to related parties		$ 775	775
NJNG to PennEast Affiliate
Related Party Transaction [Line Items]
Transportation precedent agreement, period		15 years
Transportation capacity under precedent agreement from NJNG with PennEast (in Dths per day) | DTH		180
NJRES to PennEast Affiliate
Related Party Transaction [Line Items]
Transportation precedent agreement, period		5 years
Transportation capacity under precedent agreement from NJNG with PennEast (in Dths per day) | DTH		50
NJRES to Steckman Ridge Affiliate - Energy Services
Related Party Transaction [Line Items]
Demand fees recognized pertaining to related party agreement		$ 2,134	2,775	$ 2,750
Due to related parties		$ 15	$ 375