SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, GAS IN STORAGE (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012 MMcf	Sep. 30, 2011 MMcf
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	52,600	59,900
Gas in storage	$ 175,209	$ 294,475
NJNG [Member]
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	10,700	23,100
Gas in storage	67,104	159,328
NJRES [Member]
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	41,900	36,800
Gas in storage	$ 108,105	$ 135,147