REGULATION, REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015
Regulatory Assets [Line Items]
Regulatory assets-current	$ 54,286	$ 24,258
Regulatory assets-noncurrent	441,294	410,155
Regulatory Liabilities [Line Items]
Regulatory liability-current	9,469	12,154
Regulatory liabilities-noncurrent	41,411	67,533
Conservation Incentive Program
Regulatory Liabilities [Line Items]
Regulatory liability-current	0	5,167
Overrecovered gas costs
Regulatory Liabilities [Line Items]
Regulatory liability-current	9,469	6,987
Cost of removal obligation
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	30,549	54,880
New Jersey Clean Energy Program
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	10,657	11,956
Other noncurrent regulatory liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	205	697
Conservation Incentive Program
Regulatory Assets [Line Items]
Regulatory assets-current	36,957	0
New Jersey Clean Energy Program
Regulatory Assets [Line Items]
Regulatory assets-current	14,232	14,293
Derivatives at fair value, net
Regulatory Assets [Line Items]
Regulatory assets-current	3,097	9,965
Regulatory assets-noncurrent	23,384	5,153
Environmental remediation costs, Expended, net of recoveries
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	19,595	18,886
Environmental remediation costs, Liability for future expenditures
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	172,000	180,400
Deferred income taxes
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	20,273	17,460
SAVEGREEN
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	25,208	26,882
Postemployment and other benefit costs
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	157,027	140,636
Deferred Superstorm Sandy costs
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	15,201	15,201
Other noncurrent regulatory assets
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	$ 8,606	$ 5,537