DEBT - NJNG SHORT-TERM DEBT (Details)		12 Months Ended
		Sep. 30, 2018 USD ($) debt_instrument	Sep. 30, 2017 USD ($)
Letters of credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount			$ 13,400,000
Natural Gas Distribution | Letters of credit
Line of Credit Facility [Line Items]
Number of debt instruments (in debt instruments) | debt_instrument		2
Letters of credit outstanding, amount		$ 731,000	731,000
Natural Gas Distribution | Committed Credit Facilities Due May 2019 | Bank revolving credit facilities
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	$ 250,000,000	$ 250,000,000
Natural Gas Distribution | Bank revolving credit facilities
Line of Credit Facility [Line Items]
Debt instrument, term		5 years
Line of credit facility, maximum borrowing capacity, incremental increase		$ 15,000,000
Line of credit facility, maximum borrowing capacity, maximum increase		$ 50,000,000

[1] Committed credit facilities, which require commitment fees of .075 percent on the unused amounts.