BUSINESS SEGMENT AND OTHER OPERATIONS DATA, NET FINANCIAL EARNINGS LOSS RECONCILIATION (Details) (USD $)	3 Months Ended								12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
Consolidated net financial earnings									$ 113,681,000		$ 112,417,000		$ 106,533,000
Unrealized (gain) loss from derivative instruments and related transactions, net of taxes									(5,956,000)	[1],[2]	22,631,000	[1],[2]	23,320,000	[1],[2]
Effects of economic hedging related to natural gas inventory, net of taxes									4,828,000	[3]	(3,093,000)	[3]	(18,086,000)	[3]
Net income	(20,021,000)	29,155,000	45,469,000	60,206,000	(8,693,000)	(10,320,000)	54,535,000	57,357,000	114,809,000		92,879,000		101,299,000
Taxes related to unrealized gain (loss) from derivative instruments and related transactions									(3,800,000)		13,000,000		13,400,000
Taxes related to effects of economic hedging related to natural gas inventory									2,800,000		(1,800,000)		(10,500,000)
Transactions Between NJNG and NJRES [Member]
Unrealized (gain) loss from derivative instruments and related transactions, net of taxes									$ 286,000		$ 142,000		$ 130,000

[1] Excludes unrealized losses related to an intercompany transaction between NJNG and NJRES that have been eliminated in consolidation of approximately $286,000, $142,000 and $130,000 for the fiscal years ended September 30, 2013, 2012 and 2011, respectively.

[2] Amounts are net of taxes of approximately $(3.8) million, $13 million, and $13.4 million for the fiscal years ended September 30, 2013, 2012 and 2011, respectively.

[3] Amounts are net of taxes of approximately $2.8 million, $(1.8) million and $(10.5) million for the fiscal years ended September 30, 2013, 2012 and 2011, respectively.