SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013 MMcf	Sep. 30, 2012 MMcf
Public Utilities, Inventory [Line Items]
Gas in storage	$ 280,118	$ 265,193
Gas in storage (BCF)	68,600	67,700
NJNG [Member]
Public Utilities, Inventory [Line Items]
Gas in storage	63,900	145,379
Gas in storage (BCF)	12,300	22,200
NJRES [Member]
Public Utilities, Inventory [Line Items]
Gas in storage	$ 216,218	$ 119,814
Gas in storage (BCF)	56,300	45,500