BUSINESS SEGMENT AND OTHER OPERATIONS DATA - NET FINANCIAL EARNINGS LOSS RECONCILIATION (Details) (USD $)	3 Months Ended				9 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Net financial earnings (loss)	$ 9,738,000		$ 4,130,000		$ 113,895,000		$ 123,564,000
Unrealized (gain) loss from derivative instruments and related transactions, net of taxes	(27,915,000)	[1],[2]	20,834,000	[1],[2]	(14,975,000)	[1],[2]	11,126,000	[1],[2]
Effects of economic hedging related to natural gas inventory, net of taxes	8,498,000	[3]	(6,384,000)	[3]	(5,960,000)	[3]	10,866,000	[3]
Net income (loss)	29,155,000		(10,320,000)		134,830,000		101,572,000
Taxes related to unrealized loss (gain) from derivative instruments and related transactions	(17,100,000)		12,100,000		(9,200,000)		6,300,000
Taxes related to effects of economic hedging related to natural gas inventory	4,900,000		(3,700,000)		(3,500,000)		6,300,000
Transactions Between NJNG and NJRES [Member]
Unrealized (gain) loss from derivative instruments and related transactions, net of taxes	$ 708,000		$ (20,000)		$ 398,000		$ 177,000

[1] Amounts are net of taxes of approximately $(17.1) million and $12.1 million, for the three months ended and $(9.2) million and $6.3 million for the nine months ended June 30, 2013 and 2012, respectively.

[2] Excludes unrealized losses (gains) related to an intercompany transaction between NJNG and NJRES that have been eliminated in consolidation of approximately $708,000 and $(20,000) for the three months ended and $398,000 and $177,000 for the nine months ended June 30, 2013 and 2012, respectively.

[3] Amounts are net of taxes of approximately $4.9 million and $(3.7) million for the three months ended and $(3.5) million and $6.3 million for the nine months ended June 30, 2013 and 2012, respectively.