DERIVATIVE INSTRUMENTS - VOLUME (Details)	Mar. 31, 2013 MMcf		Sep. 30, 2012 MMcf
NJNG [Member] | Future [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	20,000		16,100
NJNG [Member] | Swap [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	0	[1]	3,400	[1]
NJNG [Member] | Options Held [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	1,800		0
NJRES [Member] | Future [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	1,500
NJRES [Member] | Future [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount			(28,600)
NJRES [Member] | Swap [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	0	[1]	13,200	[1]
NJRES [Member] | Options Held [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	0		4,400
NJRES [Member] | Physical [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	61,800
NJRES [Member] | Physical [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount			(3,500)

[1] In October 2012, following the implementation of Dodd-Frank, ICE converted its cleared energy “swap” contracts to “futures” contracts and the NYMEX amended their product titles to remove the word “swap” from the titles of their “futures” and “option” contracts.