REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	$ 28,064	$ 34,372
Regulatory assets-noncurrent	369,517	402,202
Regulatory liability-current	11,710	1,456
Regulatory liabilities-noncurrent	69,120	79,647
Conservation Incentive Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-current	5,958	0
Deferred Derivative Gain (Loss) [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-current	5,752	1,456
Cost of Removal Obligation [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	69,000	79,315
Derivatives Net, Noncurrent [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	3	0
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	117	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	12,635	953
New Jersey Clean Energy Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	15,429	14,532
Environmental Remediation Costs Expended, Net of Recoveries [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	31,284	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	26,054	30,004
Postemployment and Other Benefit Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	96,337	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	$ 6,317	$ 14,656