SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, LONG LIVED ASSETS HELD FOR SALE (Details) (USD $)	2 Months Ended	12 Months Ended
Nov. 25, 2013	Sep. 30, 2013	Sep. 30, 2012
Long Lived Assets Held-for-sale [Line Items]
Asset held for sale		$ 5,428,000	$ 0
Proceeds from sale of land	6,000,000
Pre-tax gain from sale of land	313,000	(766,000)
Undeveloped Land [Member]
Long Lived Assets Held-for-sale [Line Items]
Number of acres committed to a plan to sell		25.4
Asset held for sale		$ 5,400,000

Sale of Real Estate, Area

No definition available.

Name:	njr_SaleOfRealEstateArea
Namespace Prefix:	njr_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Current assets (normally turning over within one year or one business cycle if longer) that are held for sale apart from normal operations and anticipated to be sold within one year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 45

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e1107-107759

+ Details

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

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

- Details

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

- Definition

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

+ Details

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