RELATED PARTY TRANSACTIONS (Details) $ in Thousands		3 Months Ended		6 Months Ended
	Apr. 01, 2010 USD ($) Bcf	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) Bcf / d contract	Mar. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)
Related Party Transaction [Line Items]
Demand fees expense recognized pertaining to related party agreement		$ 2,087	$ 2,072	$ 4,236	$ 4,183
Demand fees payable		1,151		$ 1,151		$ 1,152
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		1,407	1,383	$ 2,855	2,793
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		680	$ 689	1,381	$ 1,390
Demand fees payable		$ 376		$ 376		$ 377
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 bcf per day) | Bcf / d				0.18