REGULATION, REGULATORY ASSETS (Details) (USD $) In Thousands	Jun. 30, 2011		Sep. 30, 2010
Regulatory Assets [Line Items]
Regulatory assets current	$ 9,531		$ 51,466
Regulatory assets noncurrent	438,729		454,601
Underrecovered gas costs [Member]
Regulatory Assets [Line Items]
Regulatory assets current	156	[1]	36,485	[1]
Conservation Incentive Program [Member]
Regulatory Assets [Line Items]
Regulatory assets current	9,375	[1]	14,960	[1]
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets current	0	[1]	21	[1]
Enviromental remediation costs expended, net of recoveries [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	73,495	[2]	75,707	[2]
Enviromental remediation costs liability for future expenditures [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	201,600	[3]	201,600	[3]
Deferred income and other taxes [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	15,010	[1]	13,860	[1]
Derivatives, net [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	7,682	[1]	16,497	[1]
Energy Efficiency Program [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	8,685	[2]	3,958	[2]
New Jersey Clean Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	21,448	[2]	30,935	[2]
Pipeline Integrity Management [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	1,148	[4]	1,148	[4]
Post Employment Benefit Costs (Note 10) [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	105,999	[1]	106,225	[1]
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets noncurrent	$ 3,662	[5]	$ 4,671	[5]

[1] Recoverable, without interest.

[2] Recoverable, with interest.

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

[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.