SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, GAS IN STORAGE (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2011 MMcf	Sep. 30, 2010 MMcf
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	59,900	67,000
Gas in storage	$ 294,475	$ 336,163
NJNG [Member]
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	23,100	24,700
Gas in storage	159,328	181,098
NJRES [Member]
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	36,800	42,300
Gas in storage	$ 135,147	$ 155,065

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.

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

Name:	us-gaap_EnergyRelatedInventoryNaturalGasInStorage
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant