DEBT, CREDIT FACILITIES (Details) (USD $)	Sep. 30, 2012		Sep. 30, 2011
NJNG [Member]
Line of Credit Facility [Line Items]
Debt Weighted Average Interest Rate	0.22%
Debt Shelf Facilities Long term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	$ 100,000,000		$ 0
Debt Weighted Average Interest Rate	2.74%		0.00%
Notes Payable to Banks [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	144,800,000		132,850,000
Debt Weighted Average Interest Rate	1.16%		0.54%
Commercial Paper [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	135,000,000		26,500,000
Debt Weighted Average Interest Rate	0.18%		0.24%
Letter of Credit [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	13,900,000		34,300,000
Letters of Credit on Behalf of NJRES [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	11,000,000
Letter of Credit on Behalf of Njrcev [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	2,900,000
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]	175,000,000	[1]
Line of Credit Facility, Remaining Borrowing Capacity	75,000,000	[2]	175,000,000	[2]
Debt Shelf Facility MetLife [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	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
Bank Credit Facilities Short term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	325,000,000	[3]	325,000,000	[3]
Line of Credit Facility, Remaining Borrowing Capacity	166,339,000	[2]	157,853,000	[2]
Line of Credit Facility, Maximum Borrowing Capacity, Incremental Increase	5,000,000
Line of Credit Facility, Maximum Borrowing Capacity, Maximum Increase	100,000,000
Bank Credit Facilities Short term [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200,000,000	[3]	200,000,000	[3]
Line of Credit Facility, Remaining Borrowing Capacity	65,000,000		173,500,000
Line of Credit Facility, Maximum Borrowing Capacity, Incremental Increase	15,000,000
Line of Credit Facility, Maximum Borrowing Capacity, Maximum Increase			50,000,000
Bank Credit Facilities, EDA Bonds [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100,000,000		100,000,000
Unsecured senior note 1.94% [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Long-term Debt	25,000,000		0
Debt Instrument, Interest Rate, Stated Percentage	1.94%
Unsecured senior note 2.51% [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Long-term Debt	25,000,000		0
Debt Instrument, Interest Rate, Stated Percentage	2.51%
Unsecured senior note 3.25% [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Long-term Debt	$ 50,000,000		$ 0
Debt Instrument, Interest Rate, Stated Percentage	3.25%

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

[2] Letters of credit outstanding total $13.9 million and $34.3 million as of September 30, 2012 and 2011, respectively, which reduces amount available.

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