REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified
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Mar. 31, 2015
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Sep. 30, 2014
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-current |
$ 34,457us-gaap_RegulatoryAssetsCurrent |
$ 26,862us-gaap_RegulatoryAssetsCurrent |
Regulatory assets-noncurrent |
351,218us-gaap_RegulatoryAssetsNoncurrent |
377,575us-gaap_RegulatoryAssetsNoncurrent |
Regulatory liability-current |
12,115us-gaap_RegulatoryLiabilityCurrent |
6,072us-gaap_RegulatoryLiabilityCurrent |
Regulatory liabilities-noncurrent |
71,623us-gaap_RegulatoryLiabilityNoncurrent |
61,326us-gaap_RegulatoryLiabilityNoncurrent |
Conservation Incentive Program [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory liability-current |
12,115us-gaap_RegulatoryLiabilityCurrent / us-gaap_RegulatoryLiabilityAxis = njr_ConservationIncentiveProgramMember |
5,752us-gaap_RegulatoryLiabilityCurrent / us-gaap_RegulatoryLiabilityAxis = njr_ConservationIncentiveProgramMember |
Regulatory liabilities-noncurrent |
14,781us-gaap_RegulatoryLiabilityNoncurrent / us-gaap_RegulatoryLiabilityAxis = njr_ConservationIncentiveProgramMember |
0us-gaap_RegulatoryLiabilityNoncurrent / us-gaap_RegulatoryLiabilityAxis = njr_ConservationIncentiveProgramMember |
Derivatives at Fair Value, Net [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory liability-current |
0us-gaap_RegulatoryLiabilityCurrent / us-gaap_RegulatoryLiabilityAxis = njr_DerivativeNetCurrentMember |
320us-gaap_RegulatoryLiabilityCurrent / us-gaap_RegulatoryLiabilityAxis = njr_DerivativeNetCurrentMember |
Cost of Removal Obligation [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory liabilities-noncurrent |
55,372us-gaap_RegulatoryLiabilityNoncurrent / us-gaap_RegulatoryLiabilityAxis = us-gaap_RemovalCostsMember |
61,163us-gaap_RegulatoryLiabilityNoncurrent / us-gaap_RegulatoryLiabilityAxis = us-gaap_RemovalCostsMember |
Derivatives Net, Noncurrent [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory liabilities-noncurrent |
0us-gaap_RegulatoryLiabilityNoncurrent / us-gaap_RegulatoryLiabilityAxis = njr_DerivativesNetNoncurrentMember |
57us-gaap_RegulatoryLiabilityNoncurrent / us-gaap_RegulatoryLiabilityAxis = njr_DerivativesNetNoncurrentMember |
Other [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory liabilities-noncurrent |
1,470us-gaap_RegulatoryLiabilityNoncurrent / us-gaap_RegulatoryLiabilityAxis = njr_OtherRegulatoryNoncurrentLiabilityMember |
106us-gaap_RegulatoryLiabilityNoncurrent / us-gaap_RegulatoryLiabilityAxis = njr_OtherRegulatoryNoncurrentLiabilityMember |
New Jersey Clean Energy Program [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-current |
6,492us-gaap_RegulatoryAssetsCurrent / us-gaap_RegulatoryAssetAxis = njr_NewJerseyCleanEnergyProgramMember |
14,285us-gaap_RegulatoryAssetsCurrent / us-gaap_RegulatoryAssetAxis = njr_NewJerseyCleanEnergyProgramMember |
Derivatives at Fair Value, Net [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-current |
24,759us-gaap_RegulatoryAssetsCurrent / us-gaap_RegulatoryAssetAxis = njr_DerivativeNetCurrentMember |
0us-gaap_RegulatoryAssetsCurrent / us-gaap_RegulatoryAssetAxis = njr_DerivativeNetCurrentMember |
Underrecovered Gas Costs [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-current |
3,206us-gaap_RegulatoryAssetsCurrent / us-gaap_RegulatoryAssetAxis = us-gaap_AssetRecoverableGasCostsMember |
12,577us-gaap_RegulatoryAssetsCurrent / us-gaap_RegulatoryAssetAxis = us-gaap_AssetRecoverableGasCostsMember |
Environmental Remediation Costs Expended, Net of Recoveries [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-noncurrent |
17,985us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = njr_EnviromentalRemediationCostsExpendedNetOfRecoveriesMember |
30,916us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = njr_EnviromentalRemediationCostsExpendedNetOfRecoveriesMember |
Environmental Remediation Costs Liability for Future Expenditures [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-noncurrent |
177,000us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_EnvironmentalRestorationCostsMember |
177,000us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_EnvironmentalRestorationCostsMember |
Deferred Income Taxes [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-noncurrent |
9,968us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_DeferredIncomeTaxChargesMember |
9,968us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_DeferredIncomeTaxChargesMember |
SAVEGREEN [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-noncurrent |
21,517us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = njr_EnergyEfficiencyProgramMember |
29,180us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = njr_EnergyEfficiencyProgramMember |
Postemployment and Other Benefit Costs [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-noncurrent |
104,500us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_PensionAndOtherPostretirementPlansCostsMember |
108,507us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_PensionAndOtherPostretirementPlansCostsMember |
Deferred Superstorm Sandy Costs [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-noncurrent |
15,207us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_StormCostsMember |
15,207us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = us-gaap_StormCostsMember |
Other [Member] |
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Regulatory Assets And Liabilities [Line Items] |
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Regulatory assets-noncurrent |
$ 5,041us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = njr_OtherRegulatoryAssetNoncurrentMember |
$ 6,797us-gaap_RegulatoryAssetsNoncurrent / us-gaap_RegulatoryAssetAxis = njr_OtherRegulatoryAssetNoncurrentMember |