DEBT, CREDIT FACILITIES (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Commercial Paper [Member] NJNG [Member]	Sep. 30, 2012 Commercial Paper [Member] NJNG [Member]	Sep. 30, 2013 Letter of Credit [Member] NJR [Member]	Sep. 30, 2012 Letter of Credit [Member] NJR [Member]	Sep. 30, 2013 Letters of Credit on Behalf of NJRES [Member] NJR [Member]	Sep. 30, 2013 Letter of Credit on Behalf of NJNG [Member] NJNG [Member]	Sep. 30, 2012 Letter of Credit on Behalf of NJNG [Member] NJNG [Member]	Sep. 30, 2013 Letter of Credit on Behalf of NJRCEV [Member] NJR [Member]	Sep. 30, 2013 Debt Shelf Facility MetLife [Member] NJR [Member]	Sep. 26, 2013 Debt Shelf Facility MetLife [Member] NJR [Member]	Sep. 30, 2013 Debt Shelf Facility Prudential [Member] NJR [Member]	Sep. 30, 2013 Bank Credit Facilities Short term [Member] NJR [Member]	Sep. 30, 2012 Bank Credit Facilities Short term [Member] NJR [Member]	Sep. 30, 2013 Bank Credit Facilities Short term [Member] NJNG [Member]	Sep. 30, 2012 Bank Credit Facilities Short term [Member] NJNG [Member]	Sep. 30, 2013 JPMC Term Loan [Member] NJR [Member]	Sep. 30, 2013 Bank Credit Facilities, EDA Bonds [Member] NJNG [Member]	Sep. 30, 2012 Bank Credit Facilities, EDA Bonds [Member] NJNG [Member]	Sep. 30, 2013 Unsecured senior note 3.25% [Member] NJR [Member]	Sep. 30, 2012 Unsecured senior note 3.25% [Member] NJR [Member]	Sep. 30, 2013 Unsecured senior note 1.94% [Member] NJR [Member]	Sep. 30, 2012 Unsecured senior note 1.94% [Member] NJR [Member]	Sep. 30, 2013 Unsecured senior note 2.51% [Member] NJR [Member]	Sep. 30, 2012 Unsecured senior note 2.51% [Member] NJR [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity					$ 10,000,000						$ 100,000,000	$ 100,000,000	$ 75,000,000	$ 325,000,000	$ 325,000,000	$ 250,000,000	$ 200,000,000		$ 100,000,000	$ 100,000,000
Long-term debt																					50,000,000	50,000,000	25,000,000	25,000,000	25,000,000	25,000,000
Stated interest rate																					3.25%		1.94%		2.51%
Line of credit facility, maximum borrowing capacity, incremental increase														5,000,000		15,000,000
Line of credit facility, maximum borrowing capacity, maximum increase														100,000,000			50,000,000
Letters of credit outstanding, amount					17,900,000	13,900,000	14,500,000	300,000	0	3,400,000
Short-term debt	365,600,000	279,800,000																100,000,000
Line of credit facility, amount outstanding			168,600,000	135,000,000										97,000,000	144,800,000			100,000,000
Debt, Weighted Average Interest Rate			0.13%	0.18%										1.00%	1.16%			0.74%
Line of Credit Facility, Remaining Borrowing Capacity			$ 81,400,000	$ 65,000,000										$ 210,110,000	$ 166,339,000			$ 0