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BUSINESS SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 6 Months Ended
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2015 | Mar. 31, 2014
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Utility | $ 374,703us-gaap_RegulatedOperatingRevenueGas |  | $ 394,528us-gaap_RegulatedOperatingRevenueGas |  | $ 583,430us-gaap_RegulatedOperatingRevenueGas |  | $ 627,997us-gaap_RegulatedOperatingRevenueGas |
Nonutility | 638,387us-gaap_UnregulatedOperatingRevenue |  | 1,185,041us-gaap_UnregulatedOperatingRevenue |  | 1,253,784us-gaap_UnregulatedOperatingRevenue |  | 1,829,977us-gaap_UnregulatedOperatingRevenue |
Total operating revenues | 1,013,090us-gaap_RegulatedAndUnregulatedOperatingRevenue |  | 1,579,569us-gaap_RegulatedAndUnregulatedOperatingRevenue |  | 1,837,214us-gaap_RegulatedAndUnregulatedOperatingRevenue |  | 2,457,974us-gaap_RegulatedAndUnregulatedOperatingRevenue |
Depreciation and amortization | 15,204us-gaap_DepreciationAndAmortization |  | 12,828us-gaap_DepreciationAndAmortization |  | 29,590us-gaap_DepreciationAndAmortization |  | 25,394us-gaap_DepreciationAndAmortization |
Interest income | 246us-gaap_InvestmentIncomeInterest | [1] | 216us-gaap_InvestmentIncomeInterest | [1] | 336us-gaap_InvestmentIncomeInterest | [1] | 512us-gaap_InvestmentIncomeInterest | [1]
Interest expense, net of capitalized interest | 6,483us-gaap_InterestExpense |  | 6,306us-gaap_InterestExpense |  | 13,678us-gaap_InterestExpense |  | 12,601us-gaap_InterestExpense |
Income tax provision (benefit) | 20,144us-gaap_IncomeTaxExpenseBenefit |  | 71,680us-gaap_IncomeTaxExpenseBenefit |  | 61,011us-gaap_IncomeTaxExpenseBenefit |  | 73,185us-gaap_IncomeTaxExpenseBenefit |
Equity in earnings of affiliates | 3,587us-gaap_IncomeLossFromEquityMethodInvestments |  | 3,233us-gaap_IncomeLossFromEquityMethodInvestments |  | 6,382us-gaap_IncomeLossFromEquityMethodInvestments |  | 5,375us-gaap_IncomeLossFromEquityMethodInvestments |
Net financial earnings (loss) | 99,143njr_NetFinancialEarningsLoss |  | 151,920njr_NetFinancialEarningsLoss |  | 154,253njr_NetFinancialEarningsLoss |  | 191,780njr_NetFinancialEarningsLoss |
Capital expenditures | 66,318us-gaap_PropertyPlantAndEquipmentAdditions |  | 56,242us-gaap_PropertyPlantAndEquipmentAdditions |  | 158,422us-gaap_PropertyPlantAndEquipmentAdditions |  | 116,765us-gaap_PropertyPlantAndEquipmentAdditions |
Investments in equity investees | 717us-gaap_PaymentsToAcquireEquityMethodInvestments |  | 0us-gaap_PaymentsToAcquireEquityMethodInvestments |  | 1,264us-gaap_PaymentsToAcquireEquityMethodInvestments |  | 0us-gaap_PaymentsToAcquireEquityMethodInvestments |
Canada |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Percentage to total operating revenues |  |  |  |  | 4.40%njr_PercentagetoTotalOperatingRevenues / us-gaap_MajorCustomersAxis = country_CA |  | 4.00%njr_PercentagetoTotalOperatingRevenues / us-gaap_MajorCustomersAxis = country_CA |
Midstream Investments [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Investments in equity investees | 717us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = njr_MidstreamInvestmentsMember |  | 0us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = njr_MidstreamInvestmentsMember |  | 1,264us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = njr_MidstreamInvestmentsMember |  | 0us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = njr_MidstreamInvestmentsMember |
Operating Segments [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Total operating revenues | 1,060,975us-gaap_RegulatedAndUnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 1,638,791us-gaap_RegulatedAndUnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 1,879,625us-gaap_RegulatedAndUnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 2,512,142us-gaap_RegulatedAndUnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |
Depreciation and amortization | 14,968us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 12,622us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 29,128us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 24,981us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |
Interest income | 287us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember | [1] | 451us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember | [1] | 616us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember | [1] | 980us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember | [1]
Interest expense, net of capitalized interest | 6,547us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 6,175us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 13,736us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 12,359us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |
Income tax provision (benefit) | 20,478us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 72,255us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 62,292us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 74,117us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |
Net financial earnings (loss) | 100,524njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 153,511njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 156,274njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 193,572njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |
Capital expenditures | 66,268us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 55,970us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 158,361us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |  | 116,288us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember |
Operating Segments [Member] | Natural Gas Distribution [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Depreciation and amortization | 10,647us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 9,972us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 21,192us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 19,807us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |
Interest income | 10us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember | [1] | 181us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember | [1] | 100us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember | [1] | 442us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember | [1]
Interest expense, net of capitalized interest | 4,388us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 3,888us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 8,997us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 7,872us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |
Income tax provision (benefit) | 23,778us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 23,725us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 37,944us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 37,908us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |
Net financial earnings (loss) | 48,594njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 47,043njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 76,780njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 74,682njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |
Capital expenditures | 33,243us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 35,484us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 69,991us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 70,885us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |
Operating Segments [Member] | Natural Gas Distribution [Member] | External Customers [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Utility | 374,703us-gaap_RegulatedOperatingRevenueGas / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_ExternalCustomersMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 394,528us-gaap_RegulatedOperatingRevenueGas / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_ExternalCustomersMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 583,430us-gaap_RegulatedOperatingRevenueGas / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_ExternalCustomersMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |  | 627,997us-gaap_RegulatedOperatingRevenueGas / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_ExternalCustomersMember / us-gaap_StatementBusinessSegmentsAxis = njr_NaturalGasDistributionMember |
Operating Segments [Member] | Energy Services [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Depreciation and amortization | 23us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 13us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 45us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 25us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |
Interest income | 13us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember | [1] | 0us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember | [1] | 13us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember | [1] | 0us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember | [1]
Interest expense, net of capitalized interest | 288us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 661us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 801us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 1,277us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |
Income tax provision (benefit) | 3,923us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 64,345us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 49,800us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 53,072us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |
Net financial earnings (loss) | 36,316njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 91,407njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 52,752njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 98,781njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |
Operating Segments [Member] | Energy Services [Member] | External Customers [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Nonutility | 626,107us-gaap_UnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_ExternalCustomersMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember | [2] | 1,173,835us-gaap_UnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_ExternalCustomersMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember | [2] | 1,226,669us-gaap_UnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_ExternalCustomersMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember | [2] | 1,807,526us-gaap_UnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_ExternalCustomersMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember | [2]
Operating Segments [Member] | Energy Services [Member] | Intercompany [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Nonutility | 56,097us-gaap_UnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_IntercompanyMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 67,749us-gaap_UnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_IntercompanyMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 59,223us-gaap_UnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_IntercompanyMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |  | 71,767us-gaap_UnregulatedOperatingRevenue / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / njr_RevenueDesignationAxis = njr_IntercompanyMember / us-gaap_StatementBusinessSegmentsAxis = njr_EnergyServicesMember |
Operating Segments [Member] | Clean Energy Ventures [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Depreciation and amortization | 4,297us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 2,635us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 7,888us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 5,146us-gaap_DepreciationAndAmortization / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |
Interest income | 22us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember | [1] | 0us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember | [1] | 22us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember | [1] | 0us-gaap_InvestmentIncomeInterest / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember | [1]
Interest expense, net of capitalized interest | 1,661us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 1,249us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 3,478us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 2,435us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |
Income tax provision (benefit) | (9,042)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | (17,388)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | (28,763)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | (19,432)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |
Net financial earnings (loss) | 13,010njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 12,807njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 22,018njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 16,421njr_NetFinancialEarningsLoss / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |
Capital expenditures | 33,025us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 20,486us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 88,370us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |  | 45,403us-gaap_PropertyPlantAndEquipmentAdditions / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = njr_CleanEnergyVenturesMember |
Operating Segments [Member] | Clean Energy Ventures [Member] | External Customers [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
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[1] | Included in other income on the Unaudited Condensed Consolidated Statements of Operations.
[2] | Includes sales to Canada, which accounted for 4.4 percent and 4 percent of total operating revenues during the six months ended March 31, 2015 and 2014, respectively.

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