BUSINESS SEGMENT AND OTHER OPERATIONS DATA, NET FINANCIAL EARNINGS LOSS RECONCILIATION (Details) (USD $)	3 Months Ended				9 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Net Financial Earnings	$ 4,130,000		$ 9,699,000		$ 123,564,000		$ 105,858,000
Unrealized Loss (Gain) from Derivative Instruments and Related Transactions Net of Taxes	20,834,000	[1],[2]	(2,875,000)	[1],[2]	11,126,000	[1],[2]	33,835,000	[1],[2]
Effects of Economic Hedging Related to Natural Gas Inventory Net of Taxes	(6,384,000)	[3]	(7,800,000)	[3]	10,866,000	[3]	(36,787,000)	[3]
Net (loss) income	(10,320,000)		20,374,000		101,572,000		108,810,000
Taxes Related to Unrealized Loss Gain from Derivative Instruments and Related Transactions	12,100,000		(1,700,000)		6,300,000		19,600,000
Taxes Related to Effects Of Economic Hedging Related To Natural Gas Inventory	(3,700,000)		(4,500,000)		6,300,000		(21,400,000)
Transactions Between NJNG and NJRES [Member]
Unrealized Loss (Gain) from Derivative Instruments and Related Transactions Net of Taxes	$ (20,000)		$ 42,000		$ 177,000		$ 74,000

[1] Excludes unrealized (gains) losses related to an intercompany transaction between NJNG and NJRES that have been eliminated in consolidation of approximately $(20,000) and $42,000 for the three months ended and $177,000, and $74,000 for the nine months ended June 30, 2012 and 2011, respectively.

[2] Includes taxes of approximately $12.1 million and $(1.7) million, for the three months ended and $6.3 million and $19.6 million for the nine months ended June 30, 2012 and 2011, respectively.

[3] Includes taxes of approximately $(3.7) million and $(4.5) million, for the three months ended and $6.3 million and $(21.4) million for the nine months ended June 30, 2012 and 2011, respectively.