DEBT, CREDIT FACILITIES (Details) (USD $)	Jun. 30, 2012		Sep. 30, 2011
Notes Payable to Banks [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	$ 218,000,000		$ 132,850,000
Debt Weighted Average Interest Rate	0.56%		0.54%
Commercial Paper [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	82,000,000		26,500,000
Debt Weighted Average Interest Rate	0.19%		0.24%
Letter of Credit [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	8,500,000		34,300,000
Debt Shelf Facilities Long term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	175,000,000	[1],[2],[3]	175,000,000	[1],[2],[3]
Debt Shelf Facility MetLife [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100,000,000		100,000,000
Debt Shelf Facility Prudential [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75,000,000		75,000,000
Bank Credit Facilities Short term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	325,000,000	[4]	325,000,000	[4]
Line of Credit Facility, Remaining Borrowing Capacity	98,464,000	[5]	157,853,000	[5]
Bank Credit Facilities Short term [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200,000,000	[4]	200,000,000	[4]
Line of Credit Facility, Remaining Borrowing Capacity	118,000,000		173,500,000
Bank Credit Facilities, EDA Bonds [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100,000,000	[1],[4]	$ 100,000,000	[1],[4]

[1] There were no borrowings outstanding as of June 30, 2012 and September 30, 2011, respectively.

[2] Uncommitted, long-term debt shelf facilities, which require no commitment fees on the unused amounts.

[3] $100 million debt shelf expires May 2013 and $75 million debt shelf expires June 2014.

[4] Committed credit facilities, which require commitment fees on the unused amounts.

[5] Letters of credit outstanding total $8.5 million and $34.3 million as of June 30, 2012 and September 30, 2011, respectively, which reduces amount available.