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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Gas in Storage (Details) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2012 MMcf | Sep. 30, 2012 MMcf
--- | --- | ---
Public Utilities, Inventory [Line Items] |  |
Gas in storage | $ 315,945 | $ 265,193
Gas in storage (BCF) | 77,400 | 67,700
NJNG [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Gas in storage | 123,624 | 145,379
Gas in storage (BCF) | 19,800 | 22,200
NJRES [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Gas in storage | $ 192,321 | $ 119,814
Gas in storage (BCF) | 57,600 | 45,500

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- Definition Gas Stored Underground Nonmonetary Number of Billion Cubic Feet of Gas in Storage as of the balance sheet date. + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of natural gas in storage, which is a mixture of gases (liquefied or otherwise), used for fuel and manufacturing purposes, which is ready for sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -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 210.5-02.6(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration