REGULATION, REGULATORY ASSETS AND LIABILITIES (Details) (USD $)	12 Months Ended
	Sep. 30, 2012 years	Sep. 30, 2011
Regulatory Assets And Liabilities [Line Items]
Regulatory assets current	$ 32,734,000	$ 17,630,000
Regulatory assets noncurrent	441,263,000	434,185,000
Regulatory Liability, Current	1,169,000	4,633,000
Regulatory liability-noncurrent	67,077,000	59,837,000
Regulatory Liability, Amortization Period	48
Overrecovered gas costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory Liability, Current	0	4,633,000
Derivative Net, Current [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory Liability, Current	1,169,000	0
Cost of removal obligation [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-noncurrent	65,994,000	59,752,000
Derivatives Net, Liabilties Noncurrent [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-noncurrent	1,000,000	0
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-noncurrent	83,000	85,000
Underrecovered gas costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets current	7,053,000	0
Conservation Incentive Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets current	25,681,000	9,178,000
Derivative Net, Current [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets current	0	8,452,000
Enviromental remediation costs expended, net of recoveries [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	59,745,000	75,646,000
Enviromental remediation costs liability for future expenditures [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	182,000,000	182,900,000
Deferred income and other taxes [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	11,405,000	10,879,000
Energy Efficiency Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	26,025,000	11,906,000
New Jersey Clean Energy Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	5,619,000	20,144,000
Post Employment Benefit Costs (Note 10) [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	142,495,000	123,827,000
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	13,974,000	8,883,000
Regulatory Asset, Maximum Amount to Be Recorded Annually	700,000
Regulatory Assets, Expense Bench Mark	1,400,000
Regulatory Assets, Threshold Of Recording Regulatory Liability When Net Liability Exceeds Amount	1,000,000
Other Regulatory Asset Noncurrent, PIM [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	$ 2,490,000