DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) (USD $)	Dec. 31, 2014	Sep. 30, 2014
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 142,338,000us-gaap_DerivativeAssetsCurrent	$ 64,223,000us-gaap_DerivativeAssetsCurrent
Derivative liabilities, current	91,425,000us-gaap_DerivativeLiabilitiesCurrent	79,863,000us-gaap_DerivativeLiabilitiesCurrent
Derivative assets, noncurrent	6,807,000us-gaap_DerivativeAssetsNoncurrent	5,654,000us-gaap_DerivativeAssetsNoncurrent
Derivative liabilities, noncurrent	5,523,000us-gaap_DerivativeLiabilitiesNoncurrent	6,690,000us-gaap_DerivativeLiabilitiesNoncurrent
Derivative assets	149,145,000us-gaap_DerivativeAssets	69,877,000us-gaap_DerivativeAssets
Derivative liabilities	96,948,000us-gaap_DerivativeLiabilities	86,553,000us-gaap_DerivativeLiabilities
Notional amount of foreign currency derivatives	6,200,000invest_DerivativeNotionalAmount
Designated as Hedging Instrument [Member] \| NJRES [Member] \| Foreign Currency Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	0	0
Derivative liabilities, current	204,000	155,000
Derivative assets	0	0
Derivative liabilities	204,000	155,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	149,145,000	69,877,000
Derivative liabilities	96,744,000	86,398,000
Not Designated as Hedging Instrument [Member] \| NJRES [Member] \| Financial Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	127,507,000	46,307,000
Derivative liabilities, current	47,314,000	46,725,000
Derivative assets, noncurrent	6,263,000	5,537,000
Derivative liabilities, noncurrent	4,489,000	6,533,000
Not Designated as Hedging Instrument [Member] \| NJRES [Member] \| Physical Forward Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	14,769,000	15,391,000
Derivative liabilities, current	24,993,000	30,778,000
Derivative assets, noncurrent	544,000	35,000
Derivative liabilities, noncurrent	1,034,000	132,000
Not Designated as Hedging Instrument [Member] \| NJNG [Member] \| Financial Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	62,000	2,525,000
Derivative liabilities, current	18,914,000	2,205,000
Derivative assets, noncurrent	0	82,000
Derivative liabilities, noncurrent	$ 0	$ 25,000

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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