EMPLOYEE BENEFIT PLANS, Defined Benefit Plans (Details) (USD $)	12 Months Ended																					12 Months Ended		12 Months Ended																12 Months Ended				12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010		Sep. 30, 2011 Regulatory Assets [Member] Pension [Member]		Sep. 30, 2010 Regulatory Assets [Member] Pension [Member]		Sep. 30, 2011 Regulatory Assets [Member] OPEB [Member]		Sep. 30, 2010 Regulatory Assets [Member] OPEB [Member]		Sep. 30, 2011 Accumulated Other Comprehensive Income, Location [Member] Pension [Member]	Sep. 30, 2010 Accumulated Other Comprehensive Income, Location [Member] Pension [Member]	Sep. 30, 2011 Accumulated Other Comprehensive Income, Location [Member] OPEB [Member]	Sep. 30, 2010 Accumulated Other Comprehensive Income, Location [Member] OPEB [Member]	Sep. 30, 2010 NJR [Member] Post Employment Benefit Costs [Member]	Sep. 30, 2010 NJNG [Member] Post Employment Benefit Costs [Member]	Sep. 30, 2010 Post Employment Benefit Costs [Member]	Sep. 30, 2011 Minimum [Member] Pension [Member]	Sep. 30, 2010 Minimum [Member] Pension [Member]	Sep. 30, 2011 Maximum [Member] Pension [Member]	Sep. 30, 2010 Maximum [Member] Pension [Member]	Sep. 30, 2011 Pension [Member]		Sep. 30, 2010 Pension [Member]		Sep. 30, 2009 Pension [Member]		Sep. 30, 2011 Pension Plans Excluding Pension Equalization Plan, Defined Benefit [Member]	Sep. 30, 2010 Pension Plans Excluding Pension Equalization Plan, Defined Benefit [Member]	Sep. 30, 2009 Pension Plans Excluding Pension Equalization Plan, Defined Benefit [Member]	Sep. 30, 2011 OPEB [Member]	Sep. 30, 2010 OPEB [Member]	Sep. 30, 2009 OPEB [Member]	Sep. 30, 2011 OPEB [Member] Minimum [Member]	Sep. 30, 2010 OPEB [Member] Minimum [Member]	Sep. 30, 2011 OPEB [Member] Maximum [Member]	Sep. 30, 2010 OPEB [Member] Maximum [Member]	Sep. 30, 2012 Us Securities [Member]	Sep. 30, 2011 Us Securities [Member]	Sep. 30, 2010 Us Securities [Member]		Sep. 30, 2012 International Securities [Member]	Sep. 30, 2011 International Securities [Member]	Sep. 30, 2010 International Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Costs Approved		$ 609,000	$ 900,000
Defined Benefit Plan, Contributions by Employer																								5,027,000	[1]	14,616,000	[1]			4,900,000	14,500,000	25,600,000	6,497,000	4,784,000	1,900,000
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year																														20,000,000
Defined Benefit Plan Estimated Future Employer Contributions Over The Next Five Years																																				5,000,000		6,000,000
Increase (Decrease) in Regulatory Assets and Liabilities																	3,200,000	2,400,000
Regulatory Asset					72,355,000	[2]	62,565,000	[2]	47,925,000	[2]	38,750,000	[2]							2,400,000
Regulated Operations, Recovery of Costs After Income Taxes																			1,600,000
Regulated Operations, Non Cash After Tax Charge																			792,000
Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year																								155,189,000	[1]	133,839,000	[1]						89,279,000	78,292,000
Service cost																								4,775,000	[1]	3,969,000	[1]	2,712,000					3,345,000	2,814,000	1,728,000
Interest cost																								8,378,000	[1]	8,196,000	[1]	7,748,000					4,845,000	4,819,000	4,057,000
Plan participants' contributions																								48,000	[1]	48,000	[1]						16,000	9,000
Actuarial loss																								8,342,000	[1]	14,439,000	[1]						3,637,000	5,333,000
Benefits paid, net of retiree subsidies received																								(5,584,000)	[1]	(5,302,000)	[1]						(2,056,000)	(1,988,000)
Benefit obligation at end of year																								171,148,000	[1]	155,189,000	[1]	133,839,000	[1]				99,066,000	89,279,000	78,292,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year																								122,865,000	[1]	100,639,000	[1]						27,644,000	22,195,000
Actual return on plan assets																								1,933,000	[1]	12,864,000	[1]						(556,000)	2,768,000
Defined Benefit Plan, Contributions by Employer																								5,027,000	[1]	14,616,000	[1]			4,900,000	14,500,000	25,600,000	6,497,000	4,784,000	1,900,000
Benefits paid, net of plan participants' contributions																								(5,536,000)	[1]	(5,254,000)	[1]						(2,157,000)	(2,103,000)
Fair value of plan asset at end of year																								124,289,000	[1]	122,865,000	[1]	100,639,000	[1]				31,428,000	27,644,000	22,195,000
Funded status																								(46,859,000)	[1]	(32,324,000)	[1]						(67,638,000)	(61,635,000)
Amounts recognized on Consolidated Balance Sheets, Postemployment benefit liability
Current																								(75,000)	[1]	(119,000)	[1]						(117,000)	(97,000)
Non-current		(114,305,000)	(93,742,000)																					(46,784,000)	[1]	(32,205,000)	[1]						(67,521,000)	(61,538,000)
Total																								(46,859,000)	[1]	(32,324,000)	[1]						(67,638,000)	(61,635,000)
Amounts Recognized in Regulatory Assets and Accumulated Other Comprehensive Income [Roll Forward]
Beginning													18,045,000	14,366,000	9,305,000	8,477,000
Beginning					62,565,000	[2]	57,140,000		38,750,000	[2]	37,784,000
Net actuarial loss (gain) arising during the period					12,912,000		7,669,000		11,592,000		3,162,000		4,987,000	4,212,000	(4,927,000)	1,342,000
Recognized actuarial loss					(3,087,000)		(2,205,000)		(2,063,000)		(1,842,000)		(859,000)	(517,000)	(549,000)	(437,000)								(3,946,000)		(2,722,000)		(554,000)					(2,612,000)	(2,279,000)	(1,067,000)
Prior service cost amortization					(35,000)		(39,000)		(68,000)		(68,000)		(13,000)	(16,000)	(7,000)	(7,000)								48,000		56,000		56,000					75,000	76,000	78,000
Recognized net initial obligation					0		0		(286,000)		(286,000)		0	0	(70,000)	(70,000)								0		0		0					356,000	356,000	357,000
Ending													22,160,000	18,045,000	3,752,000	9,305,000
Ending					72,355,000	[2]	62,565,000	[2]	47,925,000	[2]	38,750,000	[2]							2,400,000
Amounts included in regulatory assets and accumulated other comprehensive income
Net actuarial gain (loss), Regulatory Assets																								3,848,000									2,671,000
Prior service (cost) credit, Regulatory Assets																								37,000									19,000
Net Transition Obligation, Regulatory Assets																								0									286,000
Total, Regulatory Assets																								3,885,000									2,976,000
Net actuarial gain (loss), Accumulated Other Comprehensive Income																								1,167,000									223,000
Prior service (cost) credit, Accumulated Other Comprehensive Income																								9,000									6,000
Net Transition Obligation, Accumulated Other Comprehensive Income																								0									70,000
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year																								1,176,000									299,000
Accumulated benefit obligation in excess of the fair value of plan assets
Projected benefit obligation																								171,148,000		155,189,000
Accumulated benefit obligation																								151,590,000		137,130,000
Fair value of plan assets																								124,289,000		122,865,000
Components of net periodic cost
Service cost																								4,775,000	[1]	3,969,000	[1]	2,712,000					3,345,000	2,814,000	1,728,000
Interest cost																								8,378,000	[1]	8,196,000	[1]	7,748,000					4,845,000	4,819,000	4,057,000
Expected return on plan assets																								(11,490,000)		(10,306,000)		(8,753,000)					(2,472,000)	(1,939,000)	(1,996,000)
Recognized actuarial loss					3,087,000		2,205,000		2,063,000		1,842,000		859,000	517,000	549,000	437,000								3,946,000		2,722,000		554,000					2,612,000	2,279,000	1,067,000
Prior service cost amortization					(35,000)		(39,000)		(68,000)		(68,000)		(13,000)	(16,000)	(7,000)	(7,000)								48,000		56,000		56,000					75,000	76,000	78,000
Recognized net initial obligation					0		0		(286,000)		(286,000)		0	0	(70,000)	(70,000)								0		0		0					356,000	356,000	357,000
Net periodic cost																								5,657,000		4,637,000		2,317,000					8,761,000	8,405,000	5,291,000
Weighted average assumptions used to determine benefit costs
Discount rate																								5.50%		6.25%		7.75%					5.50%	6.25%	7.75%
Expected asset return																								8.25%		8.25%		9.00%					8.25%	8.25%	9.00%
Compensation increase																				2.50%		3.25%				3.75%		3.75%					3.25%	3.75%	3.75%
Weighted average assumptions used to determine obligations
Discount rate																								5.25%		5.50%		6.25%					5.25%	5.50%	6.25%
Compensation increase																					2.50%		3.25%	3.25%				3.75%					3.25%		3.75%		2.50%		3.25%
Information relating to the assumed health care cost trend rate (HCCTR)
HCCTR																																	8.20%	8.00%	8.00%
Ultimate HCCTR																																	4.80%	5.00%	5.00%
Year ultimate HCCTR reached																																	2019	2018	2018
Effect of a 1 percentage point increase in the HCCTR on year-end benefit obligation																																	17,193,000	15,474,000	13,181,000
Effect of a 1 percentage point increase in the HCCTR on total service and interest cost																																	1,751,000	1,571,000	1,083,000
Effect of a 1 percentage point decrease in the HCCTR on year-end benefit obligation																																	(13,792,000)	(12,421,000)	(10,617,000)
Effect of a 1 percentage point decrease in the HCCTR on total service and interest costs																																	(1,367,000)	(1,234,000)	(859,000)
Defined Benefit Plan, Desired Rate of Return Before Permissible Expense After Inflation		6.00%
Target allocations
Equity Securities																																								39.00%				20.00%
Fixed income	41.00%
Total	100.00%
Actual allocations
Equity securities																																									36.00%	39.00%	[3]		17.00%	21.00%	[3]
Fixed income		47.00%	40.00%	[3]
Total		100.00%	100.00%	[3]
Defined Benefit Plan, Assets Excluded from Asset Allocation Calculation			10,100,000
Estimated future benefit payments
2012																								6,098,000									2,808,000
2013																								6,340,000									3,029,000
2014																								6,710,000									3,372,000
2015																								7,061,000									3,707,000
2016																								7,470,000									4,073,000
2017-2021																								$ 46,247,000									$ 27,297,000

[1] Includes the Company's Pension Equalization Plan.

[2] Balance represents amounts recognized in accordance with ASC 715 and excludes $609,000 and $900,000 associated with a regulatory asset approved by the BPU for fiscal 2011 and 2010, respectively.

[3] The allocation of assets excludes a contribution of $10.1 million made on September 30, 2010, that was not yet invested in accordance with the plan's investment policy.