DERIVATIVE INSTRUMENTS, INCOME STATEMENT RELATED DISCLOSURES (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Foreign Currency Contracts [Member] | Gas Purchases [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (402)	$ (432)
Amount of Gain or (Loss) Reclassified from OCI into Income (Effective Portion)	557	266
Amount of Gain or (Loss) Recognized on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0
NJRES [Member] | Nondesignated [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	107,212	(251,696)	$ 25,106
NJRES [Member] | Physical Commodity Contracts [Member] | Operating Revenues [Member] | Nondesignated [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	32,568	(48,977)	1,117
NJRES [Member] | Physical Commodity Contracts [Member] | Gas Purchases [Member] | Nondesignated [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(34,438)	(83,847)	(17,194)
NJRES [Member] | Financial Commodity Contracts [Member] | Gas Purchases [Member] | Nondesignated [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	109,082	(118,872)	41,183
NJNG [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments gain (loss) recognized in regulatory assets and liabilities, net	(33,400)	$ 10,100	$ 1,800
NJNG [Member] | Treasury Lock [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments gain (loss) recognized in regulatory assets and liabilities, net	$ (4,200)