DEBT - SHORT-TERM BANK FACILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016
NJR \| Letters of credit
Short-term Debt [Line Items]
Letters of credit outstanding, amount	$ 13,400	$ 14,400
NJR \| Notes payable to banks
Short-term Debt [Line Items]
Outstanding at end of period	$ 255,000	$ 121,700
Weighted average interest rate at end of period	2.14%	1.43%
Amount available at end of period	$ 156,601	$ 288,910
NJR \| Committed Credit Facilities Due September 2020 \| Bank revolving credit facilities
Short-term Debt [Line Items]
Bank revolving credit facilities	$ 425,000	$ 425,000
NJR \| Bank revolving credit facilities
Short-term Debt [Line Items]
Commitment fee percentage	0.075%	0.075%
Natural Gas Distribution \| Commercial paper
Short-term Debt [Line Items]
Outstanding at end of period	$ 11,000	$ 0
Weighted average interest rate at end of period	1.13%	0.00%
Amount available at end of period	$ 238,269	$ 249,269
Natural Gas Distribution \| Letters of credit
Short-term Debt [Line Items]
Letters of credit outstanding, amount	$ 731	731
Natural Gas Distribution \| Bank revolving credit facilities
Short-term Debt [Line Items]
Commitment fee percentage	0.075%
Natural Gas Distribution \| Committed Credit Facilities Due May 2019 \| Bank revolving credit facilities
Short-term Debt [Line Items]
Bank revolving credit facilities	$ 250,000	$ 250,000

Weighted average interest rate of debt outstanding.

No definition available.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-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=6876686&loc=d3e534808-122878

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- 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

+ Details

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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

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
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

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