DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) (USD $)	Jun. 30, 2014	Sep. 30, 2013
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 52,619,000	$ 53,327,000
Derivative liabilities, current	78,549,000	40,390,000
Derivative assets, noncurrent	2,830,000	2,761,000
Derivative liabilities, noncurrent	5,517,000	2,458,000
Derivative assets	55,449,000	56,088,000
Derivative liabilities	84,066,000	42,848,000
Notional amount of foreign currency derivatives	4,900,000
Designated as Hedging Instrument [Member] | NJRES [Member] | Foreign Currency Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	1,000	16,000
Derivative liabilities, current	29,000	3,000
Derivative assets, noncurrent	0	0
Derivative liabilities, noncurrent	0	2,000
Derivative assets	1,000	16,000
Derivative liabilities	29,000	5,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	55,448,000	56,072,000
Derivative liabilities	84,037,000	42,843,000
Not Designated as Hedging Instrument [Member] | NJRES [Member] | Financial Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	32,452,000	38,527,000
Derivative liabilities, current	39,142,000	23,769,000
Derivative assets, noncurrent	2,737,000	2,099,000
Derivative liabilities, noncurrent	5,350,000	2,294,000
Not Designated as Hedging Instrument [Member] | NJRES [Member] | Physical Forward Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	12,214,000	11,282,000
Derivative liabilities, current	37,177,000	14,573,000
Derivative assets, noncurrent	90,000	541,000
Derivative liabilities, noncurrent	167,000	22,000
Not Designated as Hedging Instrument [Member] | NJNG [Member] | Financial Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	7,952,000	3,502,000
Derivative liabilities, current	2,201,000	2,045,000
Derivative assets, noncurrent	3,000	121,000
Derivative liabilities, noncurrent	$ 0	$ 140,000