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DERIVATIVE INSTRUMENTS - BROKER MARGIN DEPOSITS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Derivative [Line Items]
Broker margin - Current assets	$ 44,046us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations	$ 27,339us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations
NJNG [Member]
Derivative [Line Items]
Broker margin - Current assets	29,471us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations / dei_LegalEntityAxis = njr_NjngMember	1,057us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations / dei_LegalEntityAxis = njr_NjngMember
NJRES [Member]
Derivative [Line Items]
Broker margin - Current assets	$ 14,575us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations / dei_LegalEntityAxis = njr_NjresMember	$ 26,282us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations / dei_LegalEntityAxis = njr_NjresMember

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- Definition

Amount of other receivables due from broker-dealers or clearing organizations.

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- Details

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