SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, GAS IN STORAGE (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011 MMcf	Sep. 30, 2011 MMcf
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	67,900	59,900
Gas in storage	$ 292,127	$ 294,475
NJNG [Member]
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	21,600	23,100
Gas in storage	134,994	159,328
NJRES [Member]
Public Utilities, Inventory [Line Items]
Gas in storage (BCF)	46,300	36,800
Gas in storage	$ 157,133	$ 135,147