NATURE OF THE BUSINESS (Details) shares in Thousands	12 Months Ended
Sep. 30, 2017 subsidiary customer shares
Natural Gas Distribution
Investment [Line Items]
Total retail customers (in customers) \| customer	529,800
NJR Retail Holdings Corporation
Investment [Line Items]
Number of principal subsidiaries (in subsidiaries) \| subsidiary	2
Steckman Ridge
Investment [Line Items]
Ownership interest, percent	50.00%
PennEast
Investment [Line Items]
Ownership interest, percent	20.00%
Common Units
Investment [Line Items]
Ownership interest exchanged (in shares) \| shares	1,840

Line items represent reporting 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

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Number of Principal Subsidiaries

+ References

No definition available.

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- Definition

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+ References

No definition available.

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- 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=66011266&loc=d3e33918-111571

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- Definition

The number of units of other ownership interests issued in a limited partnership or master limited partnership. Does not include limited or general partners' ownership interests.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB TOPIC 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

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