DEBT - CREDIT FACILITIES (Details) - USD ($)		Dec. 31, 2015	Sep. 30, 2015
NJR [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount		$ 22,900,000	$ 16,500,000
NJR [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Bank revolving credit facilities	[1]	425,000,000	425,000,000
Amount outstanding at end of period		$ 135,000,000	$ 39,350,000
Weighted average interest rate at end of period		1.24%	1.17%
Amount available at end of period	[2]	$ 267,055,000	$ 369,176,000
NJR [Member] | Term Loan [Member]
Line of Credit Facility [Line Items]
Bank revolving credit facilities	[3]	0	100,000,000
Amount available at end of period		0	100,000,000
NJNG [Member] | Commercial Paper [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period		$ 76,000,000	$ 27,000,000
Weighted average interest rate at end of period		0.28%	0.20%
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 revolving credit facilities	[1]	250,000,000	250,000,000
NJNG [Member] | Revolving Credit Facility [Member] | Commercial Paper [Member]
Line of Credit Facility [Line Items]
Amount available at end of period	[4]	$ 173,269,000	$ 222,269,000

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

[2] Letters of credit outstanding total $22.9 million and $16.5 million as of December 31, 2015 and September 30, 2015, 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 December 31, 2015 and September 30, 2015, respectively, which reduces the amount available by the same amount.