DEBT - CREDIT FACILITIES (Details) (USD $)	Dec. 31, 2012		Sep. 30, 2012
Commercial Paper [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period	$ 204,800,000		$ 135,000,000
Weighted average interest rate at end of period	0.19%		0.18%
Debt Shelf Facilities Long term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period	100,000,000		100,000,000
Weighted average interest rate at end of period	2.74%		2.74%
Notes Payable to Banks [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period	189,600,000		144,800,000
Weighted average interest rate at end of period	1.11%		1.16%
Letter of Credit [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	18,900,000		13,900,000
Bank Credit Facilities, EDA Bonds [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	100,000,000	[1],[2]	100,000,000	[1],[2]
Bank Credit Facilities Short term [Member] | NJNG [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	250,000,000	[2]	200,000,000	[2]
Amount available at end of period	45,200,000		65,000,000
Bank Credit Facilities Short term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	325,000,000	[2]	325,000,000	[2]
Amount available at end of period	116,510,000	[3]	166,339,000	[3]
Debt Shelf Facilities Long term [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	175,000,000	[4],[5]	175,000,000	[4],[5]
Amount available at end of period	75,000,000		75,000,000
Debt Shelf Facility MetLife [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	100,000,000		100,000,000
Debt Shelf Facility Prudential [Member] | NJR [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	$ 75,000,000		$ 75,000,000

[1] There were no borrowings outstanding as of December 31, 2012 and September 30, 2012, respectively.

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

[3] Letters of credit outstanding total $18.9 million and $13.9 million as of December 31, 2012 and September 30, 2012, respectively, which reduces amount available.

[4] $100 million debt shelf expires May 2013 and $75 million debt shelf expires June 2014.

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