RELATED PARTY TRANSACTIONS (Details) $ in Thousands		3 Months Ended		9 Months Ended
	Apr. 01, 2010 USD ($) Bcf	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Bcf / d contract	Jun. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement		$ 2,126	$ 2,156	$ 6,455	$ 6,392
Demand fees payable		1,150		$ 1,150		$ 1,150
Number of asset management agreements | contract				4
NJNG to NJRES Affilate
Related Party Transaction [Line Items]
Asset management agreement, period	10 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		1,431	1,451	$ 4,349	4,306
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		695	$ 705	2,106	$ 2,086
Demand fees payable		$ 375		$ 375		$ 375
NJNG to PennEast Affiliate
Related Party Transaction [Line Items]
Transportation precedent agreement, period				15 years
Transportation capacity under precedent agreement with PennEast (in bcf per day) | Bcf / d				0.18
NJRES to PennEast Affiliate
Related Party Transaction [Line Items]
Transportation precedent agreement, period				5 years
Transportation capacity under precedent agreement with PennEast (in bcf per day) | Bcf / d				0.05