Line of Credit Facility, Issuance period

No definition available.

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

- Definition

Long-term Debt, Number of Debt Outstanding

+ References

No definition available.

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-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=6877327&loc=d3e13212-122682

+ Details

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

- Details

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

+ Details

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

- Definition

The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

+ References

+ Details

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

- Definition

The cash outflow from the repayment of a long-term debt instrument issued, 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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

+ Details

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

- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

+ Details

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

- Definition

The gross proceeds received from the asset(s) sold in connection with the transaction involving the sale of property to another party and the lease back to the seller.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 40

-Section 55

-Paragraph 51

-URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51840-112757

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 40

-Section 55

-Paragraph 52

-URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51843-112757

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 40

-Section 55

-Paragraph 50

-URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51831-112757

+ Details

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

DEBT - SCHEDULE OF LONG TERM DEBT (Details) (USD $)	9 Months Ended		0 Months Ended		24 Months Ended				9 Months Ended		9 Months Ended	3 Months Ended		0 Months Ended		0 Months Ended		0 Months Ended		9 Months Ended
DEBT - SCHEDULE OF LONG TERM DEBT (Details) (USD $)	Jun. 30, 2014	Jun. 30, 2013	Jul. 23, 2014 Subsequent Event [Member]	Jul. 23, 2014 NJR [Member] Unsecured senior note 3.48% [Member] Subsequent Event [Member]	May 10, 2013 NJR [Member] Debt Shelf Facility Metlife [Member]	Jun. 30, 2014 NJR [Member] Debt Shelf Facility Metlife [Member] Unsecured Senior Notes [Member] note	Jun. 30, 2014 NJR [Member] Debt Shelf Facility Metlife [Member] Unsecured Senior Note 1.94% [Member]	Jun. 30, 2014 NJR [Member] Debt Shelf Facility Metlife [Member] Unsecured Senior Note 2.51% [Member]	Jun. 30, 2014 NJR [Member] Debt Shelf Facility Prudential [Member]	Jun. 30, 2014 NJR [Member] Debt Shelf Facility Prudential [Member] Unsecured Senior Note 3.25% [Member]	Jun. 30, 2014 NJR [Member] Debt Shelf Facility Metlife 2 [Member]	Dec. 31, 2013 NJNG [Member]	Dec. 31, 2012 NJNG [Member]	Mar. 13, 2014 NJNG [Member] First Mortgage [Member] Series QQ [Member]	Jun. 30, 2014 NJNG [Member] First Mortgage [Member] Series QQ [Member]	Mar. 13, 2014 NJNG [Member] First Mortgage [Member] Series RR [Member]	Jun. 30, 2014 NJNG [Member] First Mortgage [Member] Series RR [Member]	May 27, 2014 NJNG [Member] First Mortgage [Member] Series HH [Member]	May 27, 2014 NJNG [Member] First Mortgage [Member] Series HH [Member]	Jun. 30, 2014 NJNG [Member] Unsecured Debt [Member]	Mar. 14, 2014 NJNG [Member] Unsecured Debt [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					$ 100,000,000				$ 75,000,000		$ 100,000,000
Line of credit facility, issuance period					2 years				3 years		3 years
Number of debt outstanding						2
Amount issued and outstanding							25,000,000	25,000,000		50,000,000
Interest rate, stated percentage				3.48%			1.94%	2.51%		3.25%					3.58%		4.61%		5.00%		4.77%
Line of credit facility, remaining borrowing capacity											100,000,000
Proceeds from Issuance of Senior Long-term Debt			100,000,000
Debt term	3 years		10 years
Proceeds from issuance of long-term debt														70,000,000		55,000,000
Payments of long-term debt	78,964,000	5,808,000																		60,000,000
Repayments of first mortgage bond																		12,000,000
Sale leaseback transaction, gross proceeds												$ 7,600,000	$ 7,100,000