DEBT, CREDIT FACILITIES (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Sep. 30, 2011
Notes Payable to Banks [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	$ 157,300		$ 132,850
Debt Weighted Average Interest Rate	0.53%		0.54%
Commercial Paper [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	34,000		26,500
Debt Weighted Average Interest Rate	0.16%		0.24%
Debt Shelf Facilities Long term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	175,000	[1],[2],[3]	175,000	[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
Debt Shelf Facility Prudential [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75,000
Bank Credit Facilities Short term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	325,000	[4]	325,000	[4]
Line of Credit Facility, Remaining Borrowing Capacity	155,453		157,853
Bank Credit Facilities Short term [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200,000	[4]	200,000	[4]
Line of Credit Facility, Remaining Borrowing Capacity	166,000		173,500
Bank Credit Facilities, EDA Bonds [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100,000	[1],[4]	$ 100,000	[1],[4]

[1] There were no borrowings outstanding as of March 31, 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.