DERIVATIVE INSTRUMENTS - VOLUME (Details) certificate in Thousands	Jun. 30, 2017 USD ($) Bcf certificate	Sep. 30, 2016 Bcf	Jun. 01, 2015 USD ($)
Derivative [Line Items]
Derivative, notional amount | $			$ 125,000,000
Foreign currency contracts
Derivative [Line Items]
Derivative, notional amount | $	$ 919,000
NJNG | Long | Futures
Derivative [Line Items]
Volume	21.9	23.6
NJNG | Long | Physical
Derivative [Line Items]
Volume	4.9	9.2
NJRES | Physical commodity contracts
Derivative [Line Items]
Number of SRECs | certificate	309
NJRES | Long | Physical
Derivative [Line Items]
Volume	56.8	94.6
NJRES | Long | Options
Derivative [Line Items]
Volume	0.0	1.2
NJRES | Short | Futures
Derivative [Line Items]
Volume	89.3	79.1