SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, RECEIVABLE BY SUBSIDIARY (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	$ 256,461		$ 209,266
Receivable by Susidiary Percentage	100.00%		100.00%
Unbilled revenues	33,335		7,333
NJNG [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	66,098	[1]	45,092	[1]
Receivable by Susidiary Percentage	26.00%	[1]	22.00%	[1]
NJRES [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	180,464		155,594
Receivable by Susidiary Percentage	70.00%		74.00%
NJRCEV [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	49		69
Receivable by Susidiary Percentage	0.00%		0.00%
NJRHS and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	$ 9,849		$ 8,511
Receivable by Susidiary Percentage	4.00%		4.00%

[1] Does not include unbilled revenues of $33.3 million and $7.3 million as of December 31, 2011 and September 30, 2011, respectively.