<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Version>2.4.0.8</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ContextCount>595</ContextCount>
  <ElementCount>594</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>204</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>13</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ConsolidatedStatementsOfOperations</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF OPERATIONS</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002000 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002501 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ConsolidatedStatementsOfComprehensiveIncomeParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ConsolidatedStatementsOfCashFlows</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
    </Report>
    <Report>
      <IsDefault>true</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004000 - Statement - CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1004001 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1005000 - Statement - CONSOLIDATED STATEMENTS OF COMMON STOCK EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ConsolidatedStatementsOfCommonStockEquity</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMMON STOCK EQUITY</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>1005001 - Statement - CONSOLIDATED STATEMENTS OF COMMON STOCK EQUITY (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ConsolidatedStatementsOfCommonStockEquityParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMMON STOCK EQUITY (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - NATURE OF BUSINESS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/NatureOfBusiness</Role>
      <ShortName>NATURE OF BUSINESS</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPolicies</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - REGULATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/Regulation</Role>
      <ShortName>REGULATION</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2110100 - Disclosure - DERIVATIVE INSTRUMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DerivativeInstruments</Role>
      <ShortName>DERIVATIVE INSTRUMENTS</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - FAIR VALUE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/FairValue</Role>
      <ShortName>FAIR VALUE</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2116100 - Disclosure - INVESTMENTS IN EQUITY INVESTEES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/InvestmentsInEquityInvestees</Role>
      <ShortName>INVESTMENTS IN EQUITY INVESTEES</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2117100 - Disclosure - EARNINGS PER SHARE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EarningsPerShare</Role>
      <ShortName>EARNINGS PER SHARE</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2119100 - Disclosure - DEBT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/Debt</Role>
      <ShortName>DEBT</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2122100 - Disclosure - STOCK-BASED COMPENSATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/StockBasedCompensation</Role>
      <ShortName>STOCK-BASED COMPENSATION</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2125100 - Disclosure - EMPLOYEE BENEFIT PLANS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EmployeeBenefitPlans</Role>
      <ShortName>EMPLOYEE BENEFIT PLANS</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2128100 - Disclosure - ASSET RETIREMENT OBLIGATIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/AssetRetirementObligations</Role>
      <ShortName>ASSET RETIREMENT OBLIGATIONS</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2131100 - Disclosure - INCOME TAXES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/IncomeTaxes</Role>
      <ShortName>INCOME TAXES</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2134100 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/CommitmentsAndContingentLiabilities</Role>
      <ShortName>COMMITMENTS AND CONTINGENT LIABILITIES</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2137100 - Disclosure - BUSINESS SEGMENT AND OTHER OPERATIONS DATA</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/BusinessSegmentAndOtherOperationsData</Role>
      <ShortName>BUSINESS SEGMENT AND OTHER OPERATIONS DATA</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2140100 - Disclosure - RELATED PARTY TRANSACTIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/RelatedPartyTransactions</Role>
      <ShortName>RELATED PARTY TRANSACTIONS</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2143100 - Disclosure - SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SelectedQuarterlyFinancialDataUnaudited</Role>
      <ShortName>SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2146100 - Disclosure - Valuation and Qualifying Accounts</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ValuationAndQualifyingAccounts</Role>
      <ShortName>Valuation and Qualifying Accounts</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2204201 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2304302 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - REGULATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/RegulationTables</Role>
      <ShortName>REGULATION (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2310301 - Disclosure - DERIVATIVE INSTRUMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DerivativeInstrumentsTables</Role>
      <ShortName>DERIVATIVE INSTRUMENTS (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2313301 - Disclosure - FAIR VALUE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/FairValueTables</Role>
      <ShortName>FAIR VALUE (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2316301 - Disclosure - INVESTMENTS IN EQUITY INVESTEES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/InvestmentsInEquityInvesteesTables</Role>
      <ShortName>INVESTMENTS IN EQUITY INVESTEES (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2317301 - Disclosure - EARNINGS PER SHARE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EarningsPerShareTables</Role>
      <ShortName>EARNINGS PER SHARE (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2319301 - Disclosure - DEBT (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DebtTables</Role>
      <ShortName>DEBT (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2322301 - Disclosure - STOCK-BASED COMPENSATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/StockBasedCompensationTables</Role>
      <ShortName>STOCK-BASED COMPENSATION (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2325301 - Disclosure - EMPLOYEE BENEFIT PLANS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EmployeeBenefitPlansTables</Role>
      <ShortName>EMPLOYEE BENEFIT PLANS (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2328301 - Disclosure - ASSET RETIREMENT OBLIGATIONS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/AssetRetirementObligationsTables</Role>
      <ShortName>ASSET RETIREMENT OBLIGATIONS (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2331301 - Disclosure - INCOME TAXES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/IncomeTaxesTables</Role>
      <ShortName>INCOME TAXES (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2334301 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/CommitmentsAndContingentLiabilitiesTables</Role>
      <ShortName>COMMITMENTS AND CONTINGENT LIABILITIES (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2337301 - Disclosure - BUSINESS SEGMENT AND OTHER OPERATIONS DATA (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/BusinessSegmentAndOtherOperationsDataTables</Role>
      <ShortName>BUSINESS SEGMENT AND OTHER OPERATIONS DATA (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2343301 - Disclosure - SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SelectedQuarterlyFinancialDataUnauditedTables</Role>
      <ShortName>SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2401401 - Disclosure - NATURE OF BUSINESS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/NatureOfBusinessDetails</Role>
      <ShortName>NATURE OF BUSINESS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2404403 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, GAS IN STORAGE (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesGasInStorageDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, GAS IN STORAGE (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2404404 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DEMAND FEES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesDemandFeesDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DEMAND FEES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2404405 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, CAPITALIZED AND DEFERRED INTEREST (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesCapitalizedAndDeferredInterestDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, CAPITALIZED AND DEFERRED INTEREST (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2404406 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, SALES TAX ACCOUNTING (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesSalesTaxAccountingDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, SALES TAX ACCOUNTING (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2404407 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, CASH AND CASH EQUIVALENTS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesCashAndCashEquivalentsDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, CASH AND CASH EQUIVALENTS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2404408 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, PROPERTY PLANT AND EQUIPMENT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesPropertyPlantAndEquipmentDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, PROPERTY PLANT AND EQUIPMENT (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2404409 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, SALE OF ASSET (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesSaleOfAssetDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, SALE OF ASSET (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2404410 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DISPOSAL OF EQUIPMENT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesDisposalOfEquipmentDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DISPOSAL OF EQUIPMENT (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2404411 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, AVAILABLE FOR SALE SECURITIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesAvailableForSaleSecuritiesDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, AVAILABLE FOR SALE SECURITIES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2404412 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, INVESTMENT IN EQUITY INVESTEES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesInvestmentInEquityInvesteesDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, INVESTMENT IN EQUITY INVESTEES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2404413 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RECEIVABLE BY SUBSIDIARY (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesReceivableBySubsidiaryDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RECEIVABLE BY SUBSIDIARY (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2404414 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, LOAN RECEIVABLE (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesLoanReceivableDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, LOAN RECEIVABLE (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2404415 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DEFINED BENEFIT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesDefinedBenefitDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DEFINED BENEFIT (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2404416 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, ACCUMULATED OTHER COMPREHENSIVE INCOME (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SummaryOfSignificantAccountingPoliciesAccumulatedOtherComprehensiveIncomeDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, ACCUMULATED OTHER COMPREHENSIVE INCOME (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - REGULATION, REGULATORY ASSETS AND LIABILITIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/RegulationRegulatoryAssetsAndLiabilitiesDetails</Role>
      <ShortName>REGULATION, REGULATORY ASSETS AND LIABILITIES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - REGULATION, REGULATORY FILINGS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/RegulationRegulatoryFilingsDetails</Role>
      <ShortName>REGULATION, REGULATORY FILINGS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2410402 - Disclosure - DERIVATIVE INSTRUMENTS, BALANCE SHEET RELATED DISCLOSURES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DerivativeInstrumentsBalanceSheetRelatedDisclosuresDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS, BALANCE SHEET RELATED DISCLOSURES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2410403 - Disclosure - DERIVATIVE INSTRUMENTS, OFFSETTING OF ASSETS AND LIABILITIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DerivativeInstrumentsOffsettingOfAssetsAndLiabilitiesDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS, OFFSETTING OF ASSETS AND LIABILITIES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2410404 - Disclosure - DERIVATIVE INSTRUMENTS, INCOME STATEMENT RELATED DISCLOSURES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DerivativeInstrumentsIncomeStatementRelatedDisclosuresDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS, INCOME STATEMENT RELATED DISCLOSURES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2410405 - Disclosure - DERIVATIVE INSTRUMENTS, VOLUME (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DerivativeInstrumentsVolumeDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS, VOLUME (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2410406 - Disclosure - DERIVATIVE INSTRUMENTS, BROKER MARGIN DEPOSITS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DerivativeInstrumentsBrokerMarginDepositsDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS, BROKER MARGIN DEPOSITS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2410407 - Disclosure - DERIVATIVE INSTRUMENTS, CREDIT RISK EXPOSURE (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DerivativeInstrumentsCreditRiskExposureDetails</Role>
      <ShortName>DERIVATIVE INSTRUMENTS, CREDIT RISK EXPOSURE (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2413402 - Disclosure - FAIR VALUE, DEBT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/FairValueDebtDetails</Role>
      <ShortName>FAIR VALUE, DEBT (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2413403 - Disclosure - FAIR VALUE, HIERARCHY (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/FairValueHierarchyDetails</Role>
      <ShortName>FAIR VALUE, HIERARCHY (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2416402 - Disclosure - INVESTMENTS IN EQUITY INVESTEES, EQUITY METHOD INVESTMENTS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/InvestmentsInEquityInvesteesEquityMethodInvestmentsDetails</Role>
      <ShortName>INVESTMENTS IN EQUITY INVESTEES, EQUITY METHOD INVESTMENTS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2416404 - Disclosure - INVESTMENTS IN EQUITY INVESTEES, COST METHOD INVESTMENTS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/InvestmentsInEquityInvesteesCostMethodInvestmentsDetails</Role>
      <ShortName>INVESTMENTS IN EQUITY INVESTEES, COST METHOD INVESTMENTS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2417402 - Disclosure - EARNINGS PER SHARE (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EarningsPerShareDetails</Role>
      <ShortName>EARNINGS PER SHARE (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2419402 - Disclosure - DEBT, SCHEDULE OF LONG TERM DEBT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DebtScheduleOfLongTermDebtDetails</Role>
      <ShortName>DEBT, SCHEDULE OF LONG TERM DEBT (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2419403 - Disclosure - DEBT, CREDIT FACILITIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/DebtCreditFacilitiesDetails</Role>
      <ShortName>DEBT, CREDIT FACILITIES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>2422402 - Disclosure - STOCK-BASED COMPENSATION (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/StockBasedCompensationDetails</Role>
      <ShortName>STOCK-BASED COMPENSATION (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>2425402 - Disclosure - EMPLOYEE BENEFIT PLANS, DEFINED BENEFIT PLANS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EmployeeBenefitPlansDefinedBenefitPlansDetails</Role>
      <ShortName>EMPLOYEE BENEFIT PLANS, DEFINED BENEFIT PLANS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>2425403 - Disclosure - EMPLOYEE BENEFIT PLANS, ESTIMATED SUBSIDY PAYMENTS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EmployeeBenefitPlansEstimatedSubsidyPaymentsDetails</Role>
      <ShortName>EMPLOYEE BENEFIT PLANS, ESTIMATED SUBSIDY PAYMENTS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>2425404 - Disclosure - EMPLOYEE BENEFIT PLANS, FAIR VALUE (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EmployeeBenefitPlansFairValueDetails</Role>
      <ShortName>EMPLOYEE BENEFIT PLANS, FAIR VALUE (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>2425405 - Disclosure - EMPLOYEE BENEFIT PLANS, DEFINED CONTRIBUTION (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/EmployeeBenefitPlansDefinedContributionDetails</Role>
      <ShortName>EMPLOYEE BENEFIT PLANS, DEFINED CONTRIBUTION (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>2428402 - Disclosure - ASSET RETIREMENT OBLIGATIONS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/AssetRetirementObligationsDetails</Role>
      <ShortName>ASSET RETIREMENT OBLIGATIONS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>2431402 - Disclosure - INCOME TAXES, INCOME TAX RECONCILIATION (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/IncomeTaxesIncomeTaxReconciliationDetails</Role>
      <ShortName>INCOME TAXES, INCOME TAX RECONCILIATION (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>2431403 - Disclosure - INCOME TAXES, COMPONENTS OF INCOME TAX PROVISION (BENEFIT) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/IncomeTaxesComponentsOfIncomeTaxProvisionBenefitDetails</Role>
      <ShortName>INCOME TAXES, COMPONENTS OF INCOME TAX PROVISION (BENEFIT) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>2431404 - Disclosure - INCOME TAXES, DEFERRED TAX ASSETS AND LIABILITIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails</Role>
      <ShortName>INCOME TAXES, DEFERRED TAX ASSETS AND LIABILITIES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>2431405 - Disclosure - INCOME TAXES, UNRECOGNIZED TAX BENEFIT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/IncomeTaxesUnrecognizedTaxBenefitDetails</Role>
      <ShortName>INCOME TAXES, UNRECOGNIZED TAX BENEFIT (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>2431406 - Disclosure - INCOME TAXES, INCOME TAX CARRYFORWARDS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/IncomeTaxesIncomeTaxCarryforwardsDetails</Role>
      <ShortName>INCOME TAXES, INCOME TAX CARRYFORWARDS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>2434402 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES, SCHEDULE OF FUTURE COMMITTED EXPENSES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/CommitmentsAndContingentLiabilitiesScheduleOfFutureCommittedExpensesDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENT LIABILITIES, SCHEDULE OF FUTURE COMMITTED EXPENSES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>2434403 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES, CAPITAL EXPENDITURES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/CommitmentsAndContingentLiabilitiesCapitalExpendituresDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENT LIABILITIES, CAPITAL EXPENDITURES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>2434404 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES, GUARANTEES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/CommitmentsAndContingentLiabilitiesGuaranteesDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENT LIABILITIES, GUARANTEES (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>2434405 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES, LEGAL PROCEEDINGS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/CommitmentsAndContingentLiabilitiesLegalProceedingsDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENT LIABILITIES, LEGAL PROCEEDINGS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>2437402 - Disclosure - BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/BusinessSegmentAndOtherOperationsDataReconciliationOfSegmentIncomeToConsolidatedDetails</Role>
      <ShortName>BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>2437403 - Disclosure - BUSINESS SEGMENT AND OTHER OPERATIONS DATA, NET FINANCIAL EARNINGS LOSS RECONCILIATION (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/BusinessSegmentAndOtherOperationsDataNetFinancialEarningsLossReconciliationDetails</Role>
      <ShortName>BUSINESS SEGMENT AND OTHER OPERATIONS DATA, NET FINANCIAL EARNINGS LOSS RECONCILIATION (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>2437404 - Disclosure - BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/BusinessSegmentAndOtherOperationsDataReconciliationOfSegmentAssetsToConsolidatedDetails</Role>
      <ShortName>BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>2440401 - Disclosure - RELATED PARTY TRANSACTIONS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/RelatedPartyTransactionsDetails</Role>
      <ShortName>RELATED PARTY TRANSACTIONS (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>2443402 - Disclosure - SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/SelectedQuarterlyFinancialDataUnauditedDetails</Role>
      <ShortName>SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>2446401 - Disclosure - Valuation and Qualifying Accounts (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.njresources.com/role/ValuationAndQualifyingAccountsDetails</Role>
      <ShortName>Valuation and Qualifying Accounts (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">Element njr_DevelopmentProjectCosts had a mix of decimals attribute values: -6 -5.</Log>
    <Log type="Info">Element njr_NumberofMegawatts had a mix of decimals attribute values: 0 1.</Log>
    <Log type="Info">Element njr_RegulatoryCostsApproved had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element njr_ShareBasedCompensationPercentOfAwardsToCommonStock had a mix of decimals attribute values: 2 3.</Log>
    <Log type="Info">Element us-gaap_AdditionalCollateralAggregateFairValue had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element us-gaap_AvailableForSaleSecurities had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element us-gaap_CommonStockSharesOutstanding had a mix of decimals attribute values: -3 0.</Log>
    <Log type="Info">Element us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsGeneralBusiness had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element us-gaap_DefinedBenefitPlanContributionsByEmployer had a mix of decimals attribute values: -6 -5 -3 0.</Log>
    <Log type="Info">Element us-gaap_DefinedBenefitPlanCostOfProvidingSpecialOrContractualTerminationBenefitRecognizedDuringPeriod had a mix of decimals attribute values: -6 -3.</Log>
    <Log type="Info">Element us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations had a mix of decimals attribute values: 0 2.</Log>
    <Log type="Info">Element us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount had a mix of decimals attribute values: -6 0.</Log>
    <Log type="Info">Element us-gaap_DerivativeNetLiabilityPositionAggregateFairValue had a mix of decimals attribute values: -6 -3.</Log>
    <Log type="Info">Element us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element us-gaap_ProceedsFromIssuanceOfLongTermDebt had a mix of decimals attribute values: -6 -3.</Log>
    <Log type="Info">Element us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment had a mix of decimals attribute values: -6 -3.</Log>
    <Log type="Info">Element us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage had a mix of decimals attribute values: 3 4.</Log>
    <Log type="Info">Element us-gaap_RepaymentsOfLongTermDebt had a mix of decimals attribute values: -6 -3.</Log>
    <Log type="Info">Element us-gaap_SaleLeasebackTransactionNetProceedsFinancingActivities had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element us-gaap_SaleLeasebackTransactionOtherPaymentsRequired had a mix of decimals attribute values: -6 -3.</Log>
    <Log type="Info">Element us-gaap_ShortTermBorrowings had a mix of decimals attribute values: -3 0.</Log>
    <Log type="Info">'Monetary' elements on report '2404411 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, AVAILABLE FOR SALE SECURITIES (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2410402 - Disclosure - DERIVATIVE INSTRUMENTS, BALANCE SHEET RELATED DISCLOSURES (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2410404 - Disclosure - DERIVATIVE INSTRUMENTS, INCOME STATEMENT RELATED DISCLOSURES (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2410407 - Disclosure - DERIVATIVE INSTRUMENTS, CREDIT RISK EXPOSURE (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2416402 - Disclosure - INVESTMENTS IN EQUITY INVESTEES, EQUITY METHOD INVESTMENTS (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2416404 - Disclosure - INVESTMENTS IN EQUITY INVESTEES, COST METHOD INVESTMENTS (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Shares' elements on report '2417402 - Disclosure - EARNINGS PER SHARE (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2425402 - Disclosure - EMPLOYEE BENEFIT PLANS, DEFINED BENEFIT PLANS (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2425405 - Disclosure - EMPLOYEE BENEFIT PLANS, DEFINED CONTRIBUTION (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2431404 - Disclosure - INCOME TAXES, DEFERRED TAX ASSETS AND LIABILITIES (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2431406 - Disclosure - INCOME TAXES, INCOME TAX CARRYFORWARDS (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2434402 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES, SCHEDULE OF FUTURE COMMITTED EXPENSES (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2434404 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES, GUARANTEES (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2434405 - Disclosure - COMMITMENTS AND CONTINGENT LIABILITIES, LEGAL PROCEEDINGS (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '2440401 - Disclosure - RELATED PARTY TRANSACTIONS (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 1001000 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2012'</Log>
    <Log type="Info">Process Flow-Through: 1002000 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2014'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2012'</Log>
    <Log type="Info">Process Flow-Through: 1002501 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 1003000 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</Log>
    <Log type="Info">Process Flow-Through: 1004000 - Statement - CONSOLIDATED BALANCE SHEETS</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Sep. 30, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Sep. 30, 2011'</Log>
    <Log type="Info">Process Flow-Through: 1004001 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 1005001 - Statement - CONSOLIDATED STATEMENTS OF COMMON STOCK EQUITY (Parenthetical)</Log>
  </Logs>
  <InputFiles>
    <File>njr-20140930.xml</File>
    <File>njr-20140930.xsd</File>
    <File>njr-20140930_cal.xml</File>
    <File>njr-20140930_def.xml</File>
    <File>njr-20140930_lab.xml</File>
    <File>njr-20140930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
