REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Sep. 30, 2012
Regulatory Assets And Liabilities [Line Items]
Regulatory assets current	$ 25,978	$ 32,734
Regulatory assets noncurrent	442,208	441,263
Regulatory liability current	0	1,169
Regulatory liability noncurrent	79,025	67,077
Derivatives, net, current [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability current	0	1,169
Cost of removal obligation [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability noncurrent	64,346	65,994
Derivatives net, noncurrent [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability noncurrent	13,189	1,000
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory liability noncurrent	1,490	83
Conservation Incentive Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets current	18,383	25,681
Underrecovered gas costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets current	7,595	7,053
Environmental remediation costs expended, net of recoveries [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	48,830	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 and other taxes [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	11,405	11,405
Energy Efficiency Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	31,712	26,025
New Jersey Clean Energy Program [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	7,464	5,619
Postemployment and other benefit costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	137,700	142,495
Deferred Superstorm Storm Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	14,666	0
Other [Member]
Regulatory Assets And Liabilities [Line Items]
Regulatory assets noncurrent	$ 8,431	$ 13,974