DEBT - CREDIT FACILITIES (Details) - USD ($)		Mar. 31, 2016	Sep. 30, 2015
NJR [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount		$ 23,100,000	$ 16,500,000
NJR [Member] | Notes [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period		$ 115,500,000	$ 39,350,000
Weighted average interest rate at end of period		1.36%	1.17%
Amount available at end of period	[1]	$ 286,441,000	$ 369,176,000
NJR [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Amount available at end of period		0	100,000,000
NJR [Member] | Revolving Credit Facility [Member] | Committed Credit Facilities Due September 2020 [Member]
Line of Credit Facility [Line Items]
Bank revolving credit facilities	[2]	425,000,000	425,000,000
NJR [Member] | Revolving Credit Facility [Member] | Uncommitted Credit Facilities Due October 2015 [Member]
Line of Credit Facility [Line Items]
Bank revolving credit facilities	[3]	0	100,000,000
NJNG [Member] | Commercial Paper [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period		$ 37,000,000	$ 27,000,000
Weighted average interest rate at end of period		0.46%	0.20%
Amount available at end of period	[4]	$ 212,269,000	$ 222,269,000
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] | Committed Credit Facilities Due May 2019 [Member]
Line of Credit Facility [Line Items]
Bank revolving credit facilities	[2]	$ 250,000,000	$ 250,000,000

[1] Letters of credit outstanding total $23.1 million and $16.5 million as of March 31, 2016 and September 30, 2015, respectively, which reduces amount available by the same amount.

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

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

[4] Letters of credit outstanding total $731,000 and $731,000 as of March 31, 2016 and September 30, 2015, respectively, which reduces the amount available by the same amount.