DEBT, CREDIT FACILITIES (Details) (USD $)	Jun. 30, 2011		Sep. 30, 2010
NJR [Member] | Debt Shelf Facilities Long term [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 175,000,000	[1]	$ 0	[1]
NJR [Member] | Debt Shelf Facility MetLife [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100,000,000
NJR [Member] | Debt Shelf Facility Prudential [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75,000,000
NJR [Member] | Bank Credit Facilities Short term [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	325,000,000		325,000,000	[2]
NJNG [Member] | Bank Credit Facilities Short term [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200,000,000	[2]	200,000,000	[2]
NJR [Member] | Expired Credit Line [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	50,000,000
NJR [Member] | Notes Payable to Banks [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	138,000,000		140,600,000
Debt Weighted Average Interest Rate	0.51%		0.64%
NJNG [Member] | Commercial Paper [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	0		7,000,000
Debt Weighted Average Interest Rate	0.00%		0.26%
NJR [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	8,400,000
NJR [Member] | Letters of Credit on Behalf of NJRES [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	7,100,000
NJR [Member] | Letter of Credit on Behalf of CR&R [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	675,000
NJR [Member] | Letter of Credit on Behalf of Njrcev [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 711,000

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

[2] Committed credit facilities, which require commitment fees on the unu