SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, GAS IN STORAGE (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012 MMcf	Sep. 30, 2011 MMcf
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	65,900	59,900
Gas in storage	$ 215,159	$ 294,475
NJNG [Member]
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	20,300	23,100
Gas in storage	114,927	159,328
NJRES [Member]
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	45,600	36,800
Gas in storage	$ 100,232	$ 135,147