DEBT - SCHEDULE OF LONG TERM DEBT (Details) (USD $)	9 Months Ended	12 Months Ended
	Jun. 30, 2013 NJNG [Member]	Sep. 30, 2012 NJNG [Member]	Jun. 30, 2013 NJNG [Member] Bank Revolving Credit Facility [Member]		Sep. 30, 2012 NJNG [Member] Bank Revolving Credit Facility [Member]		Jun. 30, 2013 NJR [Member] Bank Revolving Credit Facility [Member]		Sep. 30, 2012 NJR [Member] Bank Revolving Credit Facility [Member]		Mar. 31, 2013 NJR [Member] Debt Shelf Facility Metlife [Member]	Jun. 30, 2013 Debt Shelf Facility Prudential [Member] NJR [Member]	Jun. 30, 2013 Unsecured senior note 1.94% [Member] Debt Shelf Facility Metlife [Member] NJR [Member]	Jun. 30, 2013 Unsecured senior note 2.51% [Member] Debt Shelf Facility Metlife [Member] NJR [Member]	Jun. 30, 2013 Unsecured senior note 3.25% [Member] Debt Shelf Facility Prudential [Member] NJR [Member]
Debt Instrument [Line Items]
Remaining borrowing capacity			$ 154,000,000		$ 65,000,000		$ 107,710,000	[1]	$ 166,339,000	[1]		$ 25,000,000
Sale leaseback transaction, gross proceeds	7,100,000	6,500,000
Line of credit facility, maximum borrowing capacity			250,000,000	[2]	200,000,000	[2]	325,000,000	[2]	325,000,000	[2]	100,000,000	75,000,000
Amount issued and outstanding													25,000,000	25,000,000	50,000,000
Proceeds from issuance of long-term debt	$ 50,000,000
Interest rate, stated percentage	3.15%												1.94%	2.51%	3.25%

[1] Letters of credit outstanding total $16.4 million and $13.9 million as of June 30, 2013 and September 30, 2012, respectively, which reduces amount available.

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