SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2010
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 568,470		$ 425,121		$ 612,921		$ 642,411		$ 670,901		$ 648,169		$ 976,987		$ 713,152		$ 2,248,923		$ 3,009,209		$ 2,639,304
Gross margin	45,155	[1]	28,713	[1]	115,068	[1]	120,364	[1]	36,520	[1]	71,237	[1]	136,572	[1]	82,659	[1]
Operating income (loss)	(14,306)		(19,911)		67,689		75,218		(17,646)		27,182		93,202		40,263		108,690		143,001		188,125
Net income (loss)	$ (8,693)		$ (10,320)		$ 54,535		$ 57,357		$ (7,511)		$ 20,374		$ 63,927		$ 24,509		$ 92,879		$ 101,299		$ 117,457
Earnings (loss) per share
BASIC	$ (0.21)		$ (0.25)		$ 1.31		$ 1.38		$ (0.18)		$ 0.49		$ 1.55		$ 0.59		$ 2.24		$ 2.45		$ 2.84
DILUTED	$ (0.21)		$ (0.25)		$ 1.31		$ 1.38		$ (0.18)		$ 0.49		$ 1.54		$ 0.59		$ 2.23	[2]	$ 2.44	[2]	$ 2.82	[2]

[1] Gross margin consists of operating revenue less cost of goods sold and other direct expenses at NJR's unregulated subsidiaries and utility gross margin at NJNG, which includes natural gas revenues less natural gas purchases, sales tax, a TEFA and regulatory rider expenses.

[2] There were no anti-dilutive shares excluded from the calculation of diluted earnings per share for fiscal 2012, 2011 and 2010.