DERIVATIVE INSTRUMENTS - VOLUME (Details)	Mar. 31, 2015 Bcf	Sep. 30, 2014 Bcf
NJNG [Member] | Futures [Member] | Long [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	27.2	17.3
NJRES [Member] | Futures [Member] | Short [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	(37.9)	(62.1)
NJRES [Member] | Options [Member] | Long [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	1.2	1.2
NJRES [Member] | Physical [Member] | Long [Member]
Derivative [Line Items]
Derivative, nonmonetary notional amount	74.7	28.6