DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) (USD $)	Mar. 31, 2014	Sep. 30, 2013
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 45,182,000	$ 53,327,000
Derivative liabilities, current	71,223,000	40,390,000
Derivative assets, noncurrent	2,270,000	2,761,000
Derivative liabilities, noncurrent	5,192,000	2,458,000
Derivative assets	47,452,000	56,088,000
Derivative liabilities	76,415,000	42,848,000
Notional amount of foreign currency derivatives	6,900,000
Designated as Hedging Instrument [Member] | NJRES [Member] | Foreign Currency Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	0	16,000
Derivative liabilities, current	277,000	3,000
Derivative assets, noncurrent	0	0
Derivative liabilities, noncurrent	7,000	2,000
Derivative assets	0	16,000
Derivative liabilities	284,000	5,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	47,452,000	56,072,000
Derivative liabilities	76,131,000	42,843,000
Not Designated as Hedging Instrument [Member] | NJRES [Member] | Financial Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	24,161,000	38,527,000
Derivative liabilities, current	34,380,000	23,769,000
Derivative assets, noncurrent	2,073,000	2,099,000
Derivative liabilities, noncurrent	5,074,000	2,294,000
Not Designated as Hedging Instrument [Member] | NJRES [Member] | Physical Forward Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	5,634,000	11,282,000
Derivative liabilities, current	35,568,000	14,573,000
Derivative assets, noncurrent	197,000	541,000
Derivative liabilities, noncurrent	111,000	22,000
Not Designated as Hedging Instrument [Member] | NJNG [Member] | Financial Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	15,387,000	3,502,000
Derivative liabilities, current	998,000	2,045,000
Derivative assets, noncurrent	0	121,000
Derivative liabilities, noncurrent	$ 0	$ 140,000