DEBT, NJNG SHORT-TERM DEBT (Details) - NJNG	12 Months Ended
	Sep. 30, 2016 USD ($) debt_instrument		Sep. 30, 2015 USD ($)
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
Committed Credit Facilities Due May 2019 | Bank revolving credit facilities
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 250,000,000	[1]	$ 250,000,000	[2]
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.

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