DERIVATIVE INSTRUMENTS - VOLUME (Details)	Jun. 30, 2013 MMcf		Sep. 30, 2012 MMcf
NJNG [Member] | Futures [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	17,000		16,100
NJNG [Member] | Swaps [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	0	[1]	3,400	[1]
NJNG [Member] | Options [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	700		0
NJRES [Member] | Futures [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	(50,200)		(28,600)
NJRES [Member] | Swaps [Member] | Long Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	0	[1]	13,200	[1]
NJRES [Member] | Options [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	22,100
NJRES [Member] | Physical [Member] | Short Position [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount			(3,500)

[1] In October 2012, following the implementation of the Dodd-Frank Wall Street Reform and Consumer Protection Act, the Intercontinental Exchange (ICE) converted its cleared energy “swap” contracts to “futures” contracts and the New York Mercantile Exchange (NYMEX) amended their product titles to remove the word “swap” from the titles of their “futures” and “option” contracts.