DEBT - CREDIT FACILITIES (Details) (USD $)	Dec. 31, 2014		Sep. 30, 2014
NJR [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	$ 17,700,000		$ 20,500,000
NJR [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	425,000,000	[1]	425,000,000	[1]
Amount available at end of period	327,345,000	[2]	256,484,000	[2]
NJR [Member] | Revolving Credit Facility [Member] | Notes Payable to Banks [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period	80,000,000		148,000,000
Weighted average interest rate at end of period	1.06%		1.08%
NJR [Member] | Bank Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	100,000,000	[3]	0	[3]
Amount available at end of period	100,000,000	[2]	0	[2]
NJNG [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	731,000		731,000
NJNG [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	250,000,000	[1]	250,000,000	[1]
Amount available at end of period	75,073,000	[4]	96,269,000	[4]
NJNG [Member] | Revolving Credit Facility [Member] | Commercial Paper [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period	$ 174,196,000		$ 153,000,000
Weighted average interest rate at end of period	0.15%		0.12%

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

[2] Letters of credit outstanding total $17.7 million and $20.5 million as of December 31, 2014 and September 30, 2014, respectively, which reduces amount available by the same amount.

[3] Uncommitted credit facilities, which require no commitment fees.

[4] Letters of credit outstanding total $731,000 as of December 31, 2014 and September 30, 2014, which reduces the amount available by the same amount.