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NATURE OF BUSINESS (Details)	12 Months Ended
	Sep. 30, 2014 Customers	Sep. 30, 2014 Steckman Ridge [Member]	Sep. 30, 2014 Iroquois [Member]	Oct. 31, 2014 Subsequent Event [Member] PennEast [Member]
Total retail customers	504,300
Ownership interest, percent		50.00%	5.53%	20.00%

X

- Definition

Total number of retail customers specific to NJNG

+ References

No definition available.

+ Details

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

X

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
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