REGULATION, REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Regulatory Assets [Line Items]
Regulatory assets-current	$ 24,258	$ 26,862
Regulatory assets-noncurrent	410,155	377,575
Regulatory Liabilities [Line Items]
Regulatory liability-current	12,154	6,072
Regulatory liabilities-noncurrent	67,533	61,326
Conservation Incentive Program [Member]
Regulatory Liabilities [Line Items]
Regulatory liability-current	5,167	5,752
Overrecovered Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liability-current	6,987	0
Derivatives at Fair Value, Net [Member]
Regulatory Liabilities [Line Items]
Regulatory liability-current	0	320
Regulatory liabilities-noncurrent	0	57
Cost of Removal Obligation [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	54,880	61,163
New Jersey Clean Energy Program [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	11,956	0
Other Noncurrent Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	697	106
New Jersey Clean Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory assets-current	14,293	14,285
Underrecovered Gas Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets-current	0	12,577
Derivatives at Fair Value, Net [Member]
Regulatory Assets [Line Items]
Regulatory assets-current	9,965	0
Regulatory assets-noncurrent	5,153	0
Enviromental Remediation Costs Expended, Net of Recoveries [Member]
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	18,886	30,916
Environmental Restoration Costs, Liability for Future Expenditures [Member]
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	180,400	177,000
Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	17,460	9,968
SAVEGREEN [Member]
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	26,882	29,180
Postemployment and Other Benefit Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	140,636	108,507
Deferred Superstorm Sandy Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	15,201	15,207
Other Noncurrent Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	$ 5,537	$ 6,797