DERIVATIVE INSTRUMENTS - INCOME STATEMENT RELATED DISCLOSURES (Details) (USD $)	3 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Expected reclassification from OCI into earnings	$ (32,000)
Maximum tenor	1 year 3 months 1 day
Foreign Currency Contract [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)	(151,000)	[1]	(95,000)	[1]
Amount of Gain or (Loss) Reclassified from OCI into Income (Effective Portion)	97,000		79,000
Amount of Gain or (Loss) Recognized on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0		0
NJRES [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(65,145,000)		23,361,000
NJRES [Member] | Physical Commodity Contracts [Member] | Operating Revenues [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(82,000)		(5,635,000)
NJRES [Member] | Physical Commodity Contracts [Member] | Gas Purchases [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(24,993,000)		(206,000)
NJRES [Member] | Financial Commodity Contracts [Member] | Gas Purchases [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(40,070,000)		29,202,000
NJNG [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in regulatory assets and liabilities net	$ 6,600,000		$ (6,200,000)

[1] The settlement of foreign currency transactions over the next twelve months is expected to result in the reclassification of $(32,000) from OCI into earnings. The maximum tenor is April 2015