REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Sep. 30, 2012
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	$ 21,013	$ 32,734
Regulatory assets-noncurrent	460,232	441,263
Regulatory liability-current	1,191	1,169
Regulatory liabilities-noncurrent	78,429	67,077
Derivatives at Fair Value, Net [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-current	1,191	1,169
Cost of Removal Obligation [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	77,581	65,994
Derivatives at Fair Valu, Net [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	0	1,000
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	848	83
Conservation Incentive Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	18,954	25,681
Underrecovered Gas Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	2,059	7,053
Environmental Remediation Costs Expended, Net of Recoveries [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	47,405	59,745
Environmental Remediation Costs Liability for Future Expenditures [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	182,000	182,000
Deferred Income Taxes [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	11,405	11,405
Derivatives at Fair Value, Net [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	386	0
Energy Efficiency Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	38,759	26,025
New Jersey Clean Energy Program (NJCEP) [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	16,953	5,619
Postemployment and Other Benefit Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	135,303	142,495
Deferred Superstorm Sandy Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	14,916	0
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	$ 13,105	$ 13,974