NJBPU Dividend Restriction Equity to Capitalization Ratio

No definition available.

Name:	njr_NJBPUDividendRestrictionEquitytoCapitalizationRatio
Namespace Prefix:	njr_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of First Mortgage Bonds Completed

+ References

No definition available.

+ Details

Name:	njr_NumberofFirstMortgageBondsCompleted
Namespace Prefix:	njr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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

No definition available.

+ Details

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

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from amounts received from a long-term debt instrument secured by a first mortgage deed of trust, containing a pledge of real property. The lender has the highest claim on the property in case of default.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

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

- Definition

Indebtedness divided by net capital.

+ References

No definition available.

+ Details

Name:	us-gaap_RatioOfIndebtednessToNetCapital1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_FirstMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=njr_NjngMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=njr_SeriesOoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=njr_SeriesCCCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=njr_SeriesBBBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=njr_UnsecuredSeniorNote3.76Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=njr_UnsecuredSeniorNote3.86Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=njr_FixedInterestRateMaturing2050Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=njr_FixedInterestRateMaturing2060Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

DEBT - FIRST MORTGAGE BONDS (Details) $ in Thousands	Aug. 01, 2019 USD ($) First_mortgage_bond	Apr. 18, 2019 USD ($) First_mortgage_bond	Sep. 30, 2020 USD ($)	Sep. 01, 2020 USD ($)	Jul. 23, 2020 USD ($)	Jun. 30, 2020 USD ($)	May 14, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jul. 17, 2019 USD ($)
Debt Instrument [Line Items]
NJBPU dividend restriction, equity to capitalization ratio			0.30
Debt to equity ratio			0.531
First mortgage bonds:
Debt Instrument [Line Items]
Maximum amount that can be issued			$ 1,100,000
NJNG
Debt Instrument [Line Items]
Number of first mortgage bonds completed \| First_mortgage_bond	3	3
Proceeds from reissuance of first mortgage bond	$ 97,000	$ 35,800
NJNG \| First mortgage bonds:
Debt Instrument [Line Items]
Weighted average interest rate		3.02%
NJNG \| First mortgage bonds: \| Series OO
Debt Instrument [Line Items]
Long-term debt			$ 46,500					$ 46,500
Stated interest rate			3.00%
NJNG \| First mortgage bonds: \| Series CCC
Debt Instrument [Line Items]
Long-term debt			$ 41,000					41,000
Stated interest rate			3.00%
NJNG \| First mortgage bonds: \| Series BBB
Debt Instrument [Line Items]
Long-term debt			$ 9,545					$ 9,545
Stated interest rate			2.75%
NJNG \| Unsecured Senior Note 3.76%
Debt Instrument [Line Items]
Long-term debt									$ 100,000
Stated interest rate									3.76%
NJNG \| Unsecured Senior Note 3.86%
Debt Instrument [Line Items]
Long-term debt									$ 85,000
Stated interest rate									3.86%
NJNG \| Senior Notes
Debt Instrument [Line Items]
Note purchase agreement amount				$ 75,000			$ 125,000
NJNG \| Senior Notes \| Fixed Interest Rate Maturing 2050
Debt Instrument [Line Items]
Stated interest rate				2.87%	3.13%	3.13%	3.13%
Note purchase agreement amount				$ 25,000	$ 50,000	$ 50,000	$ 100,000
NJNG \| Senior Notes \| Fixed Interest Rate Maturing 2060
Debt Instrument [Line Items]
Stated interest rate				2.97%	3.33%		3.33%
Note purchase agreement amount				$ 50,000	$ 25,000		$ 25,000