DEBT, SHORT-TERM BANK FACILITIES (Details) - USD ($)		12 Months Ended
		Sep. 30, 2015	Sep. 30, 2014		Sep. 28, 2015	Sep. 26, 2014	Aug. 31, 2014	[3]	Jun. 05, 2014	May. 15, 2014	[3]	Jan. 31, 2014
NJR [Member] | Letters of Credit [Member]
Short-term Debt [Line Items]
Bank revolving credit facilities	[1],[2]								$ 10,000,000
Letters of credit outstanding, amount		$ 16,500,000	$ 20,500,000
NJR [Member] | Bank Revolving Credit Facilities [Member]
Short-term Debt [Line Items]
Bank revolving credit facilities	[3]		425,000,000		$ 425,000,000							$ 325,000,000
Outstanding at end of period		$ 39,350,000	$ 148,000,000
Weighted average interest rate at end of period		1.17%	1.08%
Amount available at end of period	[4]	$ 369,176,000	$ 256,484,000
Commitment fee percentage		0.075%	0.10%
NJR [Member] | Term Loan [Member]
Short-term Debt [Line Items]
Bank revolving credit facilities	[2]	$ 100,000,000	$ 0
Amount available at end of period		100,000,000	0
NJNG [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Outstanding at end of period		$ 27,000,000	$ 153,000,000
Weighted average interest rate at end of period		0.20%	0.12%
NJNG [Member] | Letters of Credit [Member]
Short-term Debt [Line Items]
Letters of credit outstanding, amount		$ 731,000	$ 731,000
NJNG [Member] | Bank Revolving Credit Facilities [Member]
Short-term Debt [Line Items]
Bank revolving credit facilities			250,000,000	[1]			$ 250,000,000			$ 250,000,000
Commitment fee percentage		0.075%
NJNG [Member] | Bank Revolving Credit Facilities [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Amount available at end of period	[5]	$ 222,269,000	$ 96,269,000
NJNG [Member] | Term Loan [Member]
Short-term Debt [Line Items]
Bank revolving credit facilities						$ 100,000,000

[1] Committed credit facilities, which require commitment fees of .075 percent on the unused amounts.

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

[3] Committed credit facilities, which require commitment fees of .075 percent and .1 percent on the unused amounts as of September 30, 2015 and 2014, respectively.

[4] Letters of credit outstanding total $16.5 million and $20.5 million as of September 30, 2015 and 2014, respectively, which reduces amount available by the same amount.

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