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DERIVATIVE INSTRUMENTS - BROKER MARGIN DEPOSITS (Details) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Sep. 30, 2014
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Derivative [Line Items] |  |
Broker margin - Current (liabilities) assets | $ 19,761 us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations | $ 27,339 us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations
Broker margin - Current (liabilities) assets | (38,972)us-gaap_OtherPayablesToBrokerDealersAndClearingOrganizations | 0 us-gaap_OtherPayablesToBrokerDealersAndClearingOrganizations
NJNG [Member] |  |
Derivative [Line Items] |  |
Broker margin - Current (liabilities) assets | 19,761 us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations / dei_LegalEntityAxis = njr_NjngMember | 1,057 us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations / dei_LegalEntityAxis = njr_NjngMember
NJRES [Member] |  |
Derivative [Line Items] |  |
Broker margin - Current (liabilities) assets |  | 26,282 us-gaap_OtherReceivablesFromBrokerDealersAndClearingOrganizations / dei_LegalEntityAxis = njr_NjresMember
Broker margin - Current (liabilities) assets | $ (38,972)us-gaap_OtherPayablesToBrokerDealersAndClearingOrganizations / dei_LegalEntityAxis = njr_NjresMember |

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- Definition Amount of other payables due to broker-dealers or clearing organizations. + References No definition available. + Details
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- Definition Amount of other receivables due from broker-dealers or clearing organizations. + References No definition available. + Details
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