DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) (USD $)	Dec. 31, 2012	Sep. 30, 2012
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 45,498,000	$ 48,021,000
Derivative liabilities, current	22,633,000	42,440,000
Derivative assets, noncurrent	523,000	2,328,000
Derivative liabilities, noncurrent	1,727,000	3,133,000
Derivative assets	46,021,000	50,349,000
Derivative liabilities	24,360,000	45,573,000
Notional amount of foreign currency derivatives	6,800,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	45,893,000	50,163,000
Derivative liabilities	24,289,000	45,461,000
Foreign Exchange Contract [Member] | NJRES [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	80,000	116,000
Derivative liabilities, current	71,000	97,000
Derivative assets, noncurrent	48,000	70,000
Derivative liabilities, noncurrent	0	15,000
Derivative assets	128,000	186,000
Derivative liabilities	71,000	112,000
Financial Commodity Contracts [Member] | NJRES [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	29,289,000	22,112,000
Derivative liabilities, current	10,392,000	27,779,000
Derivative assets, noncurrent	391,000	600,000
Derivative liabilities, noncurrent	1,700,000	2,902,000
Financial Commodity Contracts [Member] | NJNG [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	2,713,000	6,203,000
Derivative liabilities, current	1,747,000	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	13,416,000	19,590,000
Derivative liabilities, current	10,423,000	9,530,000
Derivative assets, noncurrent	84,000	658,000
Derivative liabilities, noncurrent	$ 27,000	$ 216,000