DEBT, SCHEDULE OF LONG TERM DEBT (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Debt Instrument [Line Items]
Total long-term debt	$ 512,886,000	$ 525,169,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Proceeds from long-term debt	50,000,000	100,000,000	97,045,000
NJR [Member]
Debt Instrument [Line Items]
Total long-term debt	150,000,000	150,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2014	0
2015	25,000,000
2016	0
2017	50,000,000
2018	25,000,000
Thereafter	50,000,000
Present Value of Future Minimum Lease Payments, Sale Leaseback Transactions, Fiscal Year Maturity [Abstract]
2014	11,300,000
2015	10,700,000
2016	10,900,000
2017	9,800,000
2018	7,900,000
Thereafter	11,300,000
Subtotal	61,900,000
Less: interest component	(10,200,000)
Total	51,700,000
NJNG [Member]
Debt Instrument [Line Items]
Less: Current maturities of long-term debt	(68,643,000)	(7,760,000)
Total long-term debt	362,886,000	375,169,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2014	60,000,000
2015	0
2016	0
2017	0
2018	125,000,000
Thereafter	194,800,000
Sale leaseback transaction, gross proceeds	7,100,000	6,500,000	5,900,000
Sale leaseback transaction, other payments required	800,000	1,000,000	3,900,000
First Mortgage [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Amount of restricted net assets for consolidated and unconsolidated subsidiaries	510,900,000
Retained earnings, appropriated	339,800,000
Variable Demand Rate Notes [Member] | NJNG [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Maximum	12.00%
Debt Instrument, Interest Rate, Effective Percentage	0.09%
Unsecured Debt [Member] | NJR [Member]
Debt Instrument [Line Items]
Long-term debt	50,000,000	50,000,000
Stated interest rate	6.05%
Unsecured Debt [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	60,000,000	60,000,000
Stated interest rate	4.77%
Unsecured senior note 1.94% [Member] | NJR [Member]
Debt Instrument [Line Items]
Long-term debt	25,000,000	25,000,000
Stated interest rate	1.94%
Unsecured senior note 2.51% [Member] | NJR [Member]
Debt Instrument [Line Items]
Long-term debt	25,000,000	25,000,000
Stated interest rate	2.51%
Unsecured senior note 3.25% [Member] | NJR [Member]
Debt Instrument [Line Items]
Long-term debt	50,000,000	50,000,000
Stated interest rate	3.25%
Debt, Auction Rate Securities [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Proceeds from long-term debt			97,000,000
Series HH [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	12,000,000	12,000,000
Stated interest rate	5.00%
Series II [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	10,300,000	10,300,000
Stated interest rate	4.50%
Series JJ [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	10,500,000	10,500,000
Stated interest rate	4.60%
Series KK [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	15,000,000	15,000,000
Stated interest rate	4.90%
Series LL [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	125,000,000	125,000,000
Stated interest rate	5.60%
Series MM [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	9,545,000	9,545,000
Interest rate term	Variable
Series NN [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	41,000,000	41,000,000
Interest rate term	Variable
Series OO [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	46,500,000	46,500,000
Interest rate term	Variable
Series PP [Member] | First Mortgage [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	50,000,000	0
Stated interest rate	3.15%
Capital lease obligation-Buildings [Member] | Capital Lease Obligations [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	20,381,000	21,907,000
Capital lease obligation-Meters [Member] | Capital Lease Obligations [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	31,261,000	30,887,000
Capital lease obligation-Equipment [Member] | Capital Lease Obligations [Member] | NJNG [Member]
Debt Instrument [Line Items]
Long-term debt	$ 42,000	$ 290,000