Asset Management Agreement, Period

No definition available.

Name:	njr_AssetManagementAgreementPeriod
Namespace Prefix:	njr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Agreement between subsidiaries as a result of gas storage sold under asset management agreement

+ References

No definition available.

+ Details

Name:	njr_NaturalGasStorageSoldUnderAssetManagementAgreementfromNJNGtoNJRES
Namespace Prefix:	njr_
Data Type:	dtr-types:volumeItemType
Balance Type:	na
Period Type:	duration

- Definition

Natural Gas Transportation Capacity Under Precedent Agreement

+ References

No definition available.

+ Details

Name:	njr_NaturalGasTransportationCapacityUnderPrecedentAgreement
Namespace Prefix:	njr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Transportation Agreements

+ References

No definition available.

+ Details

Name:	njr_NumberOfTransportationAgreements
Namespace Prefix:	njr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Annual Projected Demand Fees based upon a related party agreement between various NJR Subsidiaries

+ References

No definition available.

+ Details

Name:	njr_ProjectedAnnualDemandFeesUnderRelatedPartyAgreement
Namespace Prefix:	njr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Related Party Transaction, Transportation Precedent Agreement Term

+ References

No definition available.

+ Details

Name:	njr_RelatedPartyTransactionTransportationPrecedentAgreementTerm
Namespace Prefix:	njr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Solar Array And Related Energy Output, Sublease Agreement Term

+ References

No definition available.

+ Details

Name:	njr_SolarArrayAndRelatedEnergyOutputSubleaseAgreementTerm
Namespace Prefix:	njr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

+ Details

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483326/850-10-50-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-13

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

+ Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=njr_NJNGToNJRESAffiliateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=njr_NjngToSteckmanRidgeAffiliateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=njr_NJNGToAdelphiaAffiliateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=njr_TransportationPrecedentAgreementOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=njr_TransportationPrecedentAgreementTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=njr_NJNGAndCleanEnergyVenturesToPPAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=njr_SubleaseAgreementOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=njr_SubleaseAgreementTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=njr_NJNGToNJRSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

RELATED PARTY TRANSACTIONS - ADDITIONAL INFORMATION (Details) $ in Millions	1 Months Ended		6 Months Ended
	Mar. 31, 2025 Bcf	Apr. 30, 2020 USD ($) Bcf	Mar. 31, 2026 numberOfAgreement dth / d
NJNG to NJRES Affiliate
Related Party Transaction [Line Items]
Asset management agreement, period		5 years
NJNG
Related Party Transaction [Line Items]
Asset management agreement, period	2 years
Natural gas sold at cost under asset management agreement (in Bcf) \| Bcf	3	3
Approximate annual demand fees under agreement \| $		$ 6.5
NJNG to Adelphia Affiliate
Related Party Transaction [Line Items]
Number of transportation agreements \| numberOfAgreement			2
NJNG to Adelphia Affiliate \| Transportation Precedent Agreement One
Related Party Transaction [Line Items]
Transportation capacity under precedent agreement (in bcf per day)			130,000
Transportation precedent agreement term			5 years
NJNG to Adelphia Affiliate \| Transportation Precedent Agreement Two
Related Party Transaction [Line Items]
Transportation capacity under precedent agreement (in bcf per day)			130,000
Transportation precedent agreement term			15 years
NJNG and Clean Energy Ventures to PPA \| Sublease Agreement One
Related Party Transaction [Line Items]
Sublease agreement term			15 years
NJNG and Clean Energy Ventures to PPA \| Sublease Agreement Two
Related Party Transaction [Line Items]
Sublease agreement term			20 years
NJNG to NJR Subsidiaries
Related Party Transaction [Line Items]
Term of contract			16 years