CONDENSED FINANCIAL INFORMATION OF PARENT COMPANY (Details) (USD $) In Thousands, unless otherwise specified	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
Income Statement [Abstract]
Operating revenues	$ 733,695	$ 767,469	$ 960,885	$ 736,019	$ 568,470	$ 425,121	$ 612,921	$ 642,411	$ 3,198,068	$ 2,248,923	$ 3,009,209
Operating expenses									3,038,837	2,140,233	2,866,208
Operating loss	31,929	(47,000)	(56,969)	(87,191)	14,306	19,911	(67,689)	(75,218)	(159,231)	(108,690)	(143,001)
Other income									4,783	2,128	3,747
Interest expense									23,979	20,844	19,623
INCOME BEFORE INCOME TAXES AND EQUITY IN EARNINGS OF AFFILIATES									140,035	89,974	127,125
Income tax provision (benefit)									35,575	7,729	37,665
Equity in earnings of subsidiaries									10,349	10,634	11,839
NET INCOME	(20,021)	29,155	45,469	60,206	(8,693)	(10,320)	54,535	57,357	114,809	92,879	101,299
Comprehensive Income (Loss) Statement [Abstract]
Other comprehensive (loss) income									9,150	(167)	1,403
Comprehensive income									123,959	92,712	102,702
Statement of Cash Flows [Abstract]
Net cash provided from operating activities									113,994	51,081	250,101
Net cash (used in) investing activities									(193,633)	(217,117)	(175,077)
Cash flows from (used in) financing activities:
Payments from long-term debt									(8,953)	(8,025)	(130,091)
Tax benefit from stock options exercised									173	780	2,007
Proceeds from common stock									37,839	13,834	13,704
Purchases of treasury stock									(26,606)	(8,768)	(10,193)
Payments of common stock dividends									(67,230)	(61,688)	(58,650)
Net proceeds (payments) of short-term debt									85,800	120,450	11,750
Cash flows from (used in) financing activities									78,099	163,105	(68,527)
Change in cash and temporary investments									(1,540)	(2,931)	6,497
Cash and cash equivalents at beginning of period				4,509				7,440	4,509	7,440	943
Cash and cash equivalents at end of period	2,969				4,509				2,969	4,509	7,440
ASSETS
Current assets	745,898				647,344				745,898	647,344
Total assets	3,004,783				2,770,005				3,004,783	2,770,005	2,649,444
CAPITALIZATION AND LIABILITIES
Current liabilities	851,833				653,139				851,833	653,139
Common stock equity	112,563				110,956				112,563	110,956
Total capitalization and liabilities	3,004,783				2,770,005				3,004,783	2,770,005
NJR [Member]
Income Statement [Abstract]
Operating revenues									0	0	0
Operating expenses									9,781	9,957	10,138
Operating loss									9,781	9,957	10,138
Other income									10,896	11,254	10,580
Interest expense									1,116	1,297	442
INCOME BEFORE INCOME TAXES AND EQUITY IN EARNINGS OF AFFILIATES									(1)	0	0
Income tax provision (benefit)									76	95	(11)
Equity in earnings of subsidiaries									114,886	92,974	101,288
NET INCOME									114,809	92,879	101,299
Comprehensive Income (Loss) Statement [Abstract]
Other comprehensive (loss) income									1,393	(505)	296
Comprehensive income									116,202	92,374	101,595
Statement of Cash Flows [Abstract]
Net cash provided from operating activities									87,447	47,491	60,937
Net cash (used in) investing activities									(102,134)	(115,236)	(54,568)
Cash flows from (used in) financing activities:
Payments from long-term debt									(64)	(1,678)	(77)
Tax benefit from stock options exercised									173	780	2,007
Proceeds from common stock									37,740	13,834	13,704
Proceeds from long-term debt									0	100,000	0
Net proceeds from associated companies									18,515	13,315	54,538
Purchases of treasury stock									(26,606)	(8,768)	(10,193)
Payments of common stock dividends									(67,230)	(61,688)	(58,650)
Net proceeds (payments) of short-term debt									52,200	11,950	(7,750)
Cash flows from (used in) financing activities									14,728	67,745	(6,421)
Change in cash and temporary investments									41	0	(52)
Cash and cash equivalents at beginning of period				5				5	5	5	57
Cash and cash equivalents at end of period	46				5				46	5	5
ASSETS
Current assets	39,734				2,778				39,734	2,778
Investments	900,336				845,023				900,336	845,023
Intercompany receivable, net	292,070				241,021				292,070	241,021
Deferred charges and other assets	5,308				4,945				5,308	4,945
Total assets	1,237,448				1,093,767				1,237,448	1,093,767
CAPITALIZATION AND LIABILITIES
Current liabilities	197,592				127,525				197,592	127,525
Long-term debt	150,000				150,000				150,000	150,000
Deferred credits and other liabilities	2,503				2,377				2,503	2,377
Common stock equity	887,353				813,865				887,353	813,865
Total capitalization and liabilities	$ 1,237,448				$ 1,093,767				$ 1,237,448	$ 1,093,767