DERIVATIVE INSTRUMENTS, VOLUME (Details)	Jun. 30, 2011 MMcf	Sep. 30, 2010 MMcf
NJNG [Member] | Future [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount		20,800
NJNG [Member] | Future [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,500
NJNG [Member] | Swap [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	10,700
NJNG [Member] | Swap [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount		8,700
NJRES [Member] | Future [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	13,600	13,000
NJRES [Member] | Swap [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	16,100	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	72,100	36,100