SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) $ in Thousands	Mar. 31, 2016 USD ($) Bcf	Sep. 30, 2015 USD ($) Bcf
Inventory [Line Items]
Gas in Storage \| $	$ 117,490	$ 163,905
Bcf \| Bcf	61.6	66.0
NJRES [Member]
Inventory [Line Items]
Gas in Storage \| $	$ 89,514	$ 93,696
Bcf \| Bcf	52.3	44.6
NJNG [Member]
Inventory [Line Items]
Gas in Storage \| $	$ 27,976	$ 70,209
Bcf \| Bcf	9.3	21.4

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

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