COMMITMENTS AND CONTINGENT LIABILITIES, LEGAL PROCEEDINGS (Details) (USD $)																																							9 Months Ended
	Jun. 30, 2011	Sep. 30, 2010	Jun. 30, 2011 Enviromental remediation costs expended, net of recoveries [Member]		Sep. 30, 2010 Enviromental remediation costs expended, net of recoveries [Member]		Jun. 30, 2011 Enviromental remediation costs liability for future expenditures [Member]		Sep. 30, 2010 Enviromental remediation costs liability for future expenditures [Member]		Jun. 30, 2011 Deferred income and other taxes [Member]		Sep. 30, 2010 Deferred income and other taxes [Member]		Jun. 30, 2011 Derivatives, net [Member]		Sep. 30, 2010 Derivatives, net [Member]		Jun. 30, 2011 Energy Efficiency Program [Member]		Sep. 30, 2010 Energy Efficiency Program [Member]		Jun. 30, 2011 New Jersey Clean Energy Program [Member]		Sep. 30, 2010 New Jersey Clean Energy Program [Member]		Jun. 30, 2011 Pipeline Integrity Management [Member]		Sep. 30, 2010 Pipeline Integrity Management [Member]		Jun. 30, 2011 Post Employment Benefit Costs (Note 10) [Member]		Sep. 30, 2010 Post Employment Benefit Costs (Note 10) [Member]		Jun. 30, 2011 Other [Member]		Sep. 30, 2010 Other [Member]		Jun. 30, 2011 Maximum [Member]	Jun. 30, 2011 Minimum [Member]
Site Contingency [Line Items]
Site Contingency, Recovery from Third Party of Environmental Remediation Cost																																							$ 20,000,000	$ 17,700,000
Regulatory assets	$ 438,729,000	$ 454,601,000	$ 73,495,000	[1]	$ 75,707,000	[1]	$ 201,600,000	[2]	$ 201,600,000	[2]	$ 15,010,000	[3]	$ 13,860,000	[3]	$ 7,682,000	[3]	$ 16,497,000	[3]	$ 8,685,000	[1]	$ 3,958,000	[1]	$ 21,448,000	[1]	$ 30,935,000	[1]	$ 1,148,000	[4]	$ 1,148,000	[4]	$ 105,999,000	[3]	$ 106,225,000	[3]	$ 3,662,000	[5]	$ 4,671,000	[5]

[1] Recoverable, with interest.

[2] Recovery will be requested when actual expenditures are incurred (see Note 13. Commitments and Contingent Liabilities)

[3] Recoverable, without interest.

[4] Recoverable, subject to BPU review and approval in the next base rate case.

[5] Recoverable, with or without interest depending on the specific program.