DERIVATIVE INSTRUMENTS, VOLUME (Details)	Mar. 31, 2012 MMcf	Sep. 30, 2011 MMcf
NJNG [Member] | Future [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	14,800	23,700
NJNG [Member] | Swap [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,300
NJNG [Member] | Swap [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount		1,800
NJNG [Member] | Options Held [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,400	1,100
NJRES [Member] | Future [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	26,000	13,800
NJRES [Member] | Swap [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	700	41,900
NJRES [Member] | Options Held [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0	0
NJRES [Member] | Physical [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	24,600	58,300