SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013 MMcf	Sep. 30, 2012 MMcf
Public Utilities, Inventory [Line Items]
Gas in storage	$ 167,663	$ 265,193
Gas in storage (BCF)	46,200	67,700
NJNG [Member]
Public Utilities, Inventory [Line Items]
Gas in storage	14,891	145,379
Gas in storage (BCF)	2,400	22,200
NJRES [Member]
Public Utilities, Inventory [Line Items]
Gas in storage	$ 152,772	$ 119,814
Gas in storage (BCF)	43,800	45,500