DEBT - CREDIT FACILITIES (Details) (USD $)	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2013 NJR [Member] Letter of Credit [Member]	Sep. 30, 2013 NJR [Member] Letter of Credit [Member]	Dec. 31, 2013 NJR [Member] Notes Payable to Banks [Member]	Sep. 30, 2013 NJR [Member] Notes Payable to Banks [Member]	Dec. 31, 2013 NJR [Member] Bank Revolving Credit Facility [Member]		Sep. 30, 2013 NJR [Member] Bank Revolving Credit Facility [Member]		Jan. 31, 2014 NJR [Member] Bank Revolving Credit Facility [Member] Subsequent Event [Member]	Jan. 24, 2014 NJR [Member] Bank Revolving Credit Facility [Member] Subsequent Event [Member]	Dec. 31, 2013 NJR [Member] Bank Term Loan [Member]		Sep. 30, 2013 NJR [Member] Bank Term Loan [Member]		Dec. 31, 2013 NJR [Member] Bank Letter of Credit Facility [Member]		Sep. 30, 2013 NJR [Member] Bank Letter of Credit Facility [Member]		Dec. 31, 2013 NJNG [Member] Letter of Credit [Member]	Sep. 30, 2013 NJNG [Member] Letter of Credit [Member]	Dec. 31, 2013 NJNG [Member] Commercial Paper [Member]	Sep. 30, 2013 NJNG [Member] Commercial Paper [Member]	Dec. 31, 2013 NJNG [Member] Bank Revolving Credit Facility [Member]		Sep. 30, 2013 NJNG [Member] Bank Revolving Credit Facility [Member]		Dec. 31, 2013 NJNG [Member] Bank Credit Facility Dedicated to EDA Bonds [Member]		Sep. 30, 2013 NJNG [Member] Bank Credit Facility Dedicated to EDA Bonds [Member]
Line of Credit Facility [Line Items]
Bank credit facilities							$ 325,000,000	[1]	$ 325,000,000	[1]	$ 425,000,000						$ 10,000,000	[2],[3]	$ 10,000,000	[2],[3]					$ 250,000,000	[1]	$ 250,000,000	[1]	$ 100,000,000	[1],[2]	$ 100,000,000	[1],[2]
Amount outstanding at end of period					223,100,000	97,000,000							100,000,000		100,000,000								180,500,000	168,600,000
Weighted average interest rate at end of period					1.09%	1.00%							0.72%		0.74%								0.15%	0.13%
Amount available at end of period							101,900,000	[4]	210,110,000	[4]			0		0										69,500,000	[5]	81,400,000	[5]
Bank term loan	503,600,000	365,600,000											100,000,000	[3]	100,000,000	[3]
Letters of credit outstanding, amount			19,800,000	17,900,000																	731,000	266,000
Line of credit facility, additional borrowing capacity												$ 50,000,000

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

[2] There were no borrowings outstanding as of December 31, 2013 and September 30, 2013, respectively.

[3] Uncommitted.

[4] Letters of credit outstanding total $19.8 million and $17.9 million as of December 31, 2013 and September 30, 2013, respectively, which reduces amount available by the same amount.

[5] Letters of credit outstanding total $731,000 and $266,000 as of December 31, 2013 and September 30, 2013, respectively, which reduces the amount available by the same amount.