DERIVATIVE INSTRUMENTS - BROKER MARGIN DEPOSITS (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Sep. 30, 2015
Derivative [Line Items]
Broker margin - Current assets	$ 21,334	$ 12,990
Broker margin - Current (liabilities)	(19,307)	(4,103)
NJNG [Member]
Derivative [Line Items]
Broker margin - Current assets	17,487	12,990
NJRES [Member]
Derivative [Line Items]
Broker margin - Current assets	3,847	0
Broker margin - Current (liabilities)	$ (19,307)	$ (4,103)