EMPLOYEE BENEFIT PLANS, Defined Benefit Plans (Details) (USD $)	12 Months Ended								12 Months Ended				12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011		Sep. 30, 2013 Us Securities [Member]	Sep. 30, 2012 Us Securities [Member]	Sep. 30, 2011 Us Securities [Member]		Sep. 30, 2013 International Securities [Member]	Sep. 30, 2012 International Securities [Member]	Sep. 30, 2011 International Securities [Member]		Sep. 30, 2012 Pension [Member]		Sep. 30, 2011 Pension [Member]		Sep. 30, 2010 Pension [Member]		Sep. 30, 2012 Pension [Member] Minimum [Member]	Sep. 30, 2011 Pension [Member] Minimum [Member]	Sep. 30, 2010 Pension [Member] Minimum [Member]	Sep. 30, 2012 Pension [Member] Maximum [Member]	Sep. 30, 2011 Pension [Member] Maximum [Member]	Sep. 30, 2010 Pension [Member] Maximum [Member]	Sep. 30, 2012 Pension Plans Excluding Pension Equalization Plan, Defined Benefit [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, 2012 OPEB [Member]	Sep. 30, 2011 OPEB [Member]	Sep. 30, 2010 OPEB [Member]	Sep. 30, 2012 OPEB [Member] Minimum [Member]	Sep. 30, 2011 OPEB [Member] Minimum [Member]	Sep. 30, 2010 OPEB [Member] Minimum [Member]	Sep. 30, 2012 OPEB [Member] Maximum [Member]	Sep. 30, 2011 OPEB [Member] Maximum [Member]	Sep. 30, 2010 OPEB [Member] Maximum [Member]	Sep. 30, 2011 Post Employment Benefit Costs [Member]	Sep. 30, 2011 Post Employment Benefit Costs [Member] NJR [Member]	Sep. 30, 2011 Post Employment Benefit Costs [Member] NJNG [Member]	Sep. 30, 2012 Regulatory Assets [Member] Pension [Member]		Sep. 30, 2011 Regulatory Assets [Member] Pension [Member]		Sep. 30, 2012 Regulatory Assets [Member] OPEB [Member]		Sep. 30, 2011 Regulatory Assets [Member] OPEB [Member]		Sep. 30, 2012 Accumulated Other Comprehensive Income, Location [Member] Pension [Member]	Sep. 30, 2011 Accumulated Other Comprehensive Income, Location [Member] Pension [Member]	Sep. 30, 2012 Accumulated Other Comprehensive Income, Location [Member] OPEB [Member]	Sep. 30, 2011 Accumulated Other Comprehensive Income, Location [Member] OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Costs Approved		$ 308,000	$ 609,000
Defined Benefit Plan, Contributions by Employer													20,080,000	[1]	5,027,000	[1]									20,000,000	4,900,000	14,500,000	5,775,000	6,497,000	4,800,000
Defined Benefit Plan Estimated Future Employer Contributions Over The Next Five Years																															4,000,000			6,000,000
Increase (Decrease) in Regulatory Assets and Liabilities																																						3,200,000	2,400,000
Regulatory Asset																																					2,400,000			80,449,000	[2]	72,355,000	[2]	58,799,000	[2]	47,925,000	[2]
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													171,148,000	[1]	155,189,000	[1]												99,066,000	89,279,000
Service cost													5,375,000	[1]	4,775,000	[1]	3,969,000											3,584,000	3,345,000	2,814,000
Interest cost													8,825,000	[1]	8,378,000	[1]	8,196,000											5,133,000	4,845,000	4,819,000
Plan participants' contributions													47,000	[1]	48,000	[1]												29,000	16,000
Defined Benefit Plan, Plan Amendments													1,083,000		0													(3,423,000)	0
Actuarial loss													30,428,000	[1]	8,342,000	[1]												18,807,000	3,637,000
Benefits paid, net of retiree subsidies received													(5,770,000)	[1]	(5,584,000)	[1]												(2,169,000)	(2,056,000)
Benefit obligation at end of year													211,136,000	[1]	171,148,000	[1]	155,189,000	[1]										121,027,000	99,066,000	89,279,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year													124,289,000	[1]	122,865,000	[1]												31,428,000	27,644,000
Actual return on plan assets													28,018,000	[1]	1,933,000	[1]												6,222,000	(556,000)
Defined Benefit Plan, Contributions by Employer													20,080,000	[1]	5,027,000	[1]									20,000,000	4,900,000	14,500,000	5,775,000	6,497,000	4,800,000
Benefits paid, net of plan participants' contributions													(5,723,000)	[1]	(5,536,000)	[1]												(2,335,000)	(2,157,000)
Fair value of plan asset at end of year													166,664,000	[1]	124,289,000	[1]	122,865,000	[1]										41,090,000	31,428,000	27,644,000
Funded status													(44,472,000)	[1]	(46,859,000)	[1]												(79,937,000)	(67,638,000)
Amounts recognized on Consolidated Balance Sheets, Postemployment benefit liability
Current													(93,000)	[1]	(75,000)	[1]												(120,000)	(117,000)
Non-current		(124,196,000)	(114,305,000)										(44,379,000)	[1]	(46,784,000)	[1]												(79,817,000)	(67,521,000)
Total													(44,472,000)	[1]	(46,859,000)	[1]												(79,937,000)	(67,638,000)
Amounts Recognized in Regulatory Assets and Accumulated Other Comprehensive Income [Roll Forward]
Beginning																																																22,160,000	18,045,000	3,752,000	9,305,000
Beginning																																								72,355,000	[2]	62,565,000		47,925,000	[2]	38,750,000
Net actuarial loss (gain) arising during the period																																								10,896,000		12,912,000		16,773,000		11,592,000		4,198,000	4,987,000	(1,442,000)	(4,927,000)
Recognized actuarial loss													(5,015,000)		(3,946,000)		(2,722,000)											(2,894,000)	(2,612,000)	(2,279,000)										(3,848,000)		(3,087,000)		(2,671,000)		(2,063,000)		(1,166,000)	(859,000)	(223,000)	(549,000)
Prior service cost amortization													46,000		48,000		56,000											25,000	75,000	76,000										1,046,000		(35,000)		(2,677,000)		(68,000)		(9,000)	(13,000)	(420,000)	(7,000)
Recognized net initial obligation													0		0		0											356,000	356,000	356,000										0		0		(551,000)		(286,000)		0	0	(156,000)	(70,000)
Ending																																																25,183,000	22,160,000	1,511,000	3,752,000
Ending																																					2,400,000			80,449,000	[2]	72,355,000	[2]	58,799,000	[2]	47,925,000	[2]
Amounts included in regulatory assets and accumulated other comprehensive income
Net actuarial gain (loss), Regulatory Assets													5,719,000															3,743,000
Prior service (cost) credit, Regulatory Assets													105,000															(301,000)
Net Transition Obligation, Regulatory Assets													0															22,000
Total, Regulatory Assets													5,824,000															3,464,000
Net actuarial gain (loss), Accumulated Other Comprehensive Income													1,928,000															114,000
Prior service (cost) credit, Accumulated Other Comprehensive Income													3,000															(54,000)
Net Transition Obligation, Accumulated Other Comprehensive Income													0															4,000
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year													1,931,000															64,000
Accumulated benefit obligation in excess of the fair value of plan assets
Projected benefit obligation													211,136,000		171,148,000
Accumulated benefit obligation													186,825,000		151,590,000
Fair value of plan assets													166,664,000		124,289,000
Components of net periodic cost
Service cost													5,375,000	[1]	4,775,000	[1]	3,969,000											3,584,000	3,345,000	2,814,000
Interest cost													8,825,000	[1]	8,378,000	[1]	8,196,000											5,133,000	4,845,000	4,819,000
Expected return on plan assets													(12,685,000)		(11,490,000)		(10,306,000)											(2,746,000)	(2,472,000)	(1,939,000)
Recognized actuarial loss													5,015,000		3,946,000		2,722,000											2,894,000	2,612,000	2,279,000										3,848,000		3,087,000		2,671,000		2,063,000		1,166,000	859,000	223,000	549,000
Prior service cost amortization													46,000		48,000		56,000											25,000	75,000	76,000										1,046,000		(35,000)		(2,677,000)		(68,000)		(9,000)	(13,000)	(420,000)	(7,000)
Recognized net initial obligation													0		0		0											356,000	356,000	356,000										0		0		(551,000)		(286,000)		0	0	(156,000)	(70,000)
Net periodic cost													6,576,000		5,657,000		4,637,000											9,246,000	8,761,000	8,405,000
Weighted average assumptions used to determine benefit costs
Discount rate													5.25%		5.50%		6.25%											5.25%	5.50%	6.25%
Expected asset return													8.25%		8.25%		8.25%											8.25%	8.25%	8.25%
Compensation increase													3.25%				3.75%			2.50%			3.25%					3.25%	3.25%	3.75%
Weighted average assumptions used to determine obligations
Discount rate													4.30%		5.25%		5.50%											4.30%	5.25%	5.50%
Compensation increase													3.25%		3.25%						2.50%			3.25%				3.25%	3.25%				2.50%			3.25%
Information relating to the assumed health care cost trend rate (HCCTR)
HCCTR																												7.50%	8.20%	8.00%
Ultimate HCCTR																												4.80%	4.80%	5.00%
Year ultimate HCCTR reached																												2022	2019	2018
Effect of a 1 percentage point increase in the HCCTR on year-end benefit obligation																												21,278,000	17,193,000	15,474,000
Effect of a 1 percentage point increase in the HCCTR on total service and interest cost																												1,868,000	1,751,000	1,571,000
Effect of a 1 percentage point decrease in the HCCTR on year-end benefit obligation																												(17,034,000)	(13,792,000)	(12,421,000)
Effect of a 1 percentage point decrease in the HCCTR on total service and interest costs																												(1,457,000)	(1,367,000)	(1,234,000)
Defined Benefit Plan, Desired Rate of Return Before Permissible Expense After Inflation		8.00%
Target allocations
Equity Securities					39.00%				20.00%
Fixed income	41.00%
Total	100.00%
Actual allocations
Equity securities						39.00%	36.00%	[3]		21.00%	17.00%	[3]
Fixed income		40.00%	47.00%	[3]
Total		100.00%	100.00%	[3]
Estimated future benefit payments
2013													6,451,000															2,865,000
2014													6,853,000															3,278,000
2015													7,289,000															3,712,000
2016													7,760,000															4,189,000
2017													8,269,000															4,688,000
2018-2022													$ 52,985,000															$ 31,951,000

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

[2] Balance represents amounts recognized in accordance with ASC 715 and excludes $308,000 and $609,000 associated with a regulatory asset approved by the BPU for fiscal 2012 and 2011, respectively.

[3]