DERIVATIVE INSTRUMENTS, BALANCE SHEET RELATED DISCLOSURES (Details) (USD $)	Mar. 31, 2012	Sep. 30, 2011
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	$ 103,506,000	$ 100,338,000
Derivative Liabilities, Current	92,028,000	68,698,000
Derivative Assets, Noncurrent	3,333,000	6,515,000
Derivative Liabilities, Noncurrent	3,751,000	6,341,000
Derivative Assets	106,839,000	106,853,000
Derivative Liabilities	95,779,000	75,039,000
Notional Amount of Foreign Currency Derivatives	11,500,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	106,619,000	106,573,000
Derivative Liabilities	95,714,000	75,025,000
Physical Commodity Contracts [Member] | NJRES [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	21,541,000	33,240,000
Derivative Liabilities, Current	11,150,000	10,570,000
Derivative Assets, Noncurrent	578,000	4,450,000
Derivative Liabilities, Noncurrent	604,000	781,000
Financial Commodity Contracts [Member] | NJRES [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	75,789,000	61,521,000
Derivative Liabilities, Current	31,139,000	44,862,000
Derivative Assets, Noncurrent	2,499,000	1,936,000
Derivative Liabilities, Noncurrent	3,104,000	4,934,000
Financial Commodity Contracts [Member] | NJNG [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	6,049,000	5,424,000
Derivative Liabilities, Current	49,717,000	13,258,000
Derivative Assets, Noncurrent	163,000	2,000
Derivative Liabilities, Noncurrent	0	620,000
Foreign Exchange Contract [Member] | NJRES [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	127,000	153,000
Derivative Liabilities, Current	22,000	8,000
Derivative Assets, Noncurrent	93,000	127,000
Derivative Liabilities, Noncurrent	43,000	6,000
Derivative Assets	220,000	280,000
Derivative Liabilities	$ 65,000	$ 14,000