DERIVATIVE INSTRUMENTS, VOLUME (Details)	Sep. 30, 2011 MMcf	Sep. 30, 2010 MMcf
NJNG [Member] | Future [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	23,700	20,800
NJNG [Member] | Swap [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,800	8,700
NJNG [Member] | Options Held [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,100	0
NJRES [Member] | Future [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	13,800	13,000
NJRES [Member] | Swap [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	41,900	7,300
NJRES [Member] | Options Held [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0	600
NJRES [Member] | Physical [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	58,300	36,100