SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, GAS IN STORAGE (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012 MMcf	Sep. 30, 2011 MMcf
Public Utilities, Inventory [Line Items]
Gas in storage	$ 265,193	$ 294,475
Gas in storage (BCF)	67,700	59,900
NJNG [Member]
Public Utilities, Inventory [Line Items]
Gas in storage	145,379	159,328
Gas in storage (BCF)	22,200	23,100
NJRES [Member]
Public Utilities, Inventory [Line Items]
Gas in storage	$ 119,814	$ 135,147
Gas in storage (BCF)	45,500	36,800