DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) (USD $)	Mar. 31, 2013	Sep. 30, 2012
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 42,152,000	$ 48,021,000
Derivative liabilities, current	46,525,000	42,440,000
Derivative assets, noncurrent	781,000	2,328,000
Derivative liabilities, noncurrent	1,310,000	3,133,000
Derivative assets	42,933,000	50,349,000
Derivative liabilities	47,835,000	45,573,000
Notional amount of foreign currency derivatives	5,200,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	42,862,000	50,163,000
Derivative liabilities	47,809,000	45,461,000
Foreign Exchange Contract [Member] | NJRES [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	57,000	116,000
Derivative liabilities, current	26,000	97,000
Derivative assets, noncurrent	14,000	70,000
Derivative liabilities, noncurrent	0	15,000
Derivative assets	71,000	186,000
Derivative liabilities	26,000	112,000
Financial Commodity Contracts [Member] | NJRES [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	16,658,000	22,112,000
Derivative liabilities, current	40,430,000	27,779,000
Derivative assets, noncurrent	706,000	600,000
Derivative liabilities, noncurrent	1,078,000	2,902,000
Financial Commodity Contracts [Member] | NJNG [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	14,768,000	6,203,000
Derivative liabilities, current	1,579,000	5,034,000
Derivative assets, noncurrent	0	1,000,000
Derivative liabilities, noncurrent	0	0
Physical Commodity Contracts [Member] | NJRES [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	10,669,000	19,590,000
Derivative liabilities, current	4,490,000	9,530,000
Derivative assets, noncurrent	61,000	658,000
Derivative liabilities, noncurrent	$ 232,000	$ 216,000