DERIVATIVE INSTRUMENTS - INCOME STATEMENT RELATED DISCLOSURES (Details) (USD $)	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Expected reclassification from OCI into earnings	$ (28,000)		$ (28,000)
Maximum tenor			0 years 9 months 1 day
NJNG [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in regulatory assets and liabilities net	1,500,000	(4,700,000)	14,300,000		1,400,000
Not Designated as Hedging Instrument [Member] | NJRES [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	61,000	34,387,000	(279,110,000)		27,617,000
Not Designated as Hedging Instrument [Member] | Physical Commodity Contracts [Member] | Operating Revenues [Member] | NJRES [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	5,496,000	3,595,000	(52,502,000)		(4,264,000)
Not Designated as Hedging Instrument [Member] | Physical Commodity Contracts [Member] | Gas Purchases [Member] | NJRES [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(7,728,000)	(8,809,000)	(87,202,000)		(6,253,000)
Not Designated as Hedging Instrument [Member] | Financial Commodity Contracts [Member] | Gas Purchases [Member] | NJRES [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	2,293,000	39,601,000	(139,406,000)		38,134,000
Cash Flow Hedging [Member] | Foreign Currency Contract [Member] | Gas Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	213,000	(14,000)	(247,000)	[1]	(85,000)	[1]
Amount of Gain or (Loss) Reclassified from OCI into Income (Effective Portion)	44,000	(21,000)	209,000		23,000
Amount of Gain or (Loss) Recognized on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	$ 0	$ 0	$ 0		$ 0

[1] The settlement of foreign currency transactions over the next twelve months is expected to result in the reclassification of $(28,000) from OCI into earnings. The maximum tenor is April 2015