REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Sep. 30, 2013
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	$ 18,970	$ 34,372
Regulatory assets-noncurrent	368,319	402,202
Regulatory liability-current	20,360	1,456
Regulatory liabilities-noncurrent	76,857	79,647
Deferred Derivative Gain (Loss) [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-current	14,396	1,456
Conservation Incentive Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-current	5,964	0
Cost of Removal Obligation [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	75,327	79,315
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	1,530	332
Conservation Incentive Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	0	18,887
Underrecovered Gas Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	12,991	953
New Jersey Clean Energy Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	5,979	14,532
Environmental Remediation Costs Expended, Net of Recoveries [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	32,661	46,968
Environmental Remediation Costs Liability for Future Expenditures [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	183,600	183,600
Deferred Income Taxes [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	10,718	10,718
Derivatives at Fair Value, Net [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	0	19
SAVEGREEN [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	23,988	30,004
Postemployment and Other Benefit Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	98,029	101,415
Deferred Superstorm Sandy Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	15,207	14,822
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	$ 4,116	$ 14,656