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COMMITMENTS AND CONTINGENT LIABILITIES - LEGAL PROCEEDINGS (Details) (USD $) | 6 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Sep. 30, 2014
Site Contingency [Line Items] |  |
Regulatory assets | $ 351,218,000us-gaap_RegulatoryAssetsNoncurrent | $ 377,575,000us-gaap_RegulatoryAssetsNoncurrent
Minimum [Member] |  |
Site Contingency [Line Items] |  |
Litigation settlement, gross | 151,300,000us-gaap_LitigationSettlementAmount / us-gaap_RangeAxis = us-gaap_MinimumMember |
Maximum [Member] |  |
Site Contingency [Line Items] |  |
Litigation settlement, gross | 249,800,000us-gaap_LitigationSettlementAmount / us-gaap_RangeAxis = us-gaap_MaximumMember |
Environmental Remediation Costs Expended, Net of Recoveries [Member] |  |
Site Contingency [Line Items] |  |
Regulatory assets | 17,985,000us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = njr_EnviromentalRemediationCostsExpendedNetOfRecoveriesMember | 30,916,000us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = njr_EnviromentalRemediationCostsExpendedNetOfRecoveriesMember
Environmental Remediation Costs Liability for Future Expenditures [Member] |  |
Site Contingency [Line Items] |  |
Regulatory assets | 177,000,000us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_EnvironmentalRestorationCostsMember | 177,000,000us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_EnvironmentalRestorationCostsMember
SBC [Member] | July 2013 SBC Filing [Member] |  |
Site Contingency [Line Items] |  |
Annual recovery amount approved by the Board of Public Utilities | 18,700,000njr_AnnualRecoveryAmountApprovedbytheBoardofPublicUtilities / njr_IncentivesorProgramsFilingPeriodAxis = njr_July2013SBCFilingMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = njr_SbcMember |
SBC [Member] | September 2014 SBC Filing [Member] |  |
Site Contingency [Line Items] |  |
Requested rate, amount | $ 8,500,000njr_PublicUtilitiesRequestedRateAmount / njr_IncentivesorProgramsFilingPeriodAxis = njr_September2014SBCFilingMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = njr_SbcMember |

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- Definition Amount of judgment or settlement awarded to (against) the entity in respect of litigation. + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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