DEBT - CREDIT FACILITIES (Details) - USD ($)		Jun. 30, 2015		Oct. 24, 2014	Sep. 30, 2014
NJR [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount		$ 12,700,000			$ 20,500,000
NJR [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	[1]	425,000,000			425,000,000
Amount available at end of period	[2]	412,345,000			256,484,000
NJR [Member] | Revolving Credit Facility [Member] | Notes Payable to Banks [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period		$ 0			$ 148,000,000
Weighted average interest rate at end of period		0.00%			1.08%
NJR [Member] | Bank Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Bank credit facilities		$ 100,000,000	[3]	$ 100,000,000	$ 0	[3]
Amount available at end of period		100,000,000			0
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	[1]	250,000,000			250,000,000
Amount available at end of period	[4]	249,269,000			96,269,000
NJNG [Member] | Revolving Credit Facility [Member] | Commercial Paper [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period		$ 0			$ 153,000,000
Weighted average interest rate at end of period		0.00%			0.12%

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

[2] Letters of credit outstanding total $12.7 million and $20.5 million as of June 30, 2015 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 and $731,000 as of June 30, 2015 and September 30, 2014, respectively, which reduces the amount available by the same amount.