SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014 MMcf	Sep. 30, 2013 MMcf
Inventory [Line Items]
Gas in Storage	$ 219,859	$ 314,477
Gas in Storage (mmcf)	53,900	82,700
NJNG [Member]
Inventory [Line Items]
Gas in Storage	48,279	104,979
Gas in Storage (mmcf)	12,100	20,400
NJRES [Member]
Inventory [Line Items]
Gas in Storage	$ 171,580	$ 209,498
Gas in Storage (mmcf)	41,800	62,300

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 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 6

-Subparagraph a

-Article 5

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