BUSINESS SEGMENT AND OTHER OPERATIONS DATA - NET FINANCIAL EARNINGS LOSS RECONCILIATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Consolidated net financial earnings	$ 4,514		$ 9,738		$ 196,295		$ 113,895
Unrealized (gain) loss from derivative instruments and related transactions	(6,585)	[1]	(44,148)	[1]	45,811	[1]	(23,682)	[1]
Effects of economic hedging related to natural gas inventory	38,139		13,440		(3,409)		(9,425)
Tax adjustments	(12,766)		11,291		(12,497)		12,172
NET (LOSS) INCOME	(14,274)		29,155		166,390		134,830
Transactions Between NJNG and NJRES [Member]
Unrealized (gains) losses related to intercompany transactions	$ (327)		$ (708)		$ 345		$ (398)

[1] Excludes unrealized (gains) losses related to an intercompany transaction between NJNG and NJRES that have been eliminated in consolidation of approximately $(327,000) and $(708,000) for the three months ended and $345,000 and $(398,000) for the nine months ended June 30, 2014 and 2013, respectively.