Wind Farm Total Capacity

No definition available.

Name:	njr_WindFarmTotalCapacity
Namespace Prefix:	njr_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

+ Details

Name:	us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

+ References

No definition available.

+ Details

Name:	us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainLossOnSaleOfPropertyPlantEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromDivestitureOfBusinesses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=njr_IssuedAndOutstandingSharesOfNRJRetailServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=njr_CleanEnergyVenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnergyAxis=srt_NaturalGasReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

DISPOSITIONS (Details) $ in Thousands			12 Months Ended
DISPOSITIONS (Details) $ in Thousands	Jun. 01, 2018 USD ($) MW	Feb. 28, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of businesses, net of closing costs			$ 27,916	$ 0	$ 0
Issued And Outstanding Shares Of NRJ Retail Services
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of businesses, net of closing costs		$ 9,500
Proceeds from sale of business		(3,700)
Clean Energy Ventures
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of business	$ (951)
Wind farm total capacity (in MW) \| MW	9.7
Disposal group consideration	$ 18,500
Natural Gas \| Issued And Outstanding Shares Of NRJ Retail Services
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Derivative gain		$ 14,600