DERIVATIVE INSTRUMENTS, INCOME STATEMENT RELATED DISCLOSURES (Details) (USD $)	12 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months	$ 13,000
Maximum date in foreign currency cash flow hedge	Apr. 30, 2015
Foreign Exchange 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)	(44,000)	[1]	(90,000)	[1]
Amount of Gain or (Loss) Reclassified from OCI into Income (Effective Portion)	(18,000)		(102,000)
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	25,106,000		87,652,000		41,004,000
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	1,117,000		(7,187,000)		41,538,000
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	(17,194,000)		12,967,000		6,474,000
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	41,183,000		81,872,000		(7,008,000)
NJNG [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments gain (loss) recognized in regulatory assets and liabilities, net	$ 1,800,000		$ (25,300,000)		$ (15,100,000)

[1] The settlement of foreign currency transactions over the next 12 months is expected to result in the reclassification of $13,097 from OCI into earnings. The maximum tenor is April 2015.