DEBT - CREDIT FACILITIES (Details) (USD $)	Jun. 30, 2014		Jan. 30, 2014		Jan. 24, 2014	Sep. 30, 2013
Line of Credit Facility [Line Items]
Bank term loan	$ 174,500,000					$ 365,600,000
NJR [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	26,700,000					17,900,000
NJR [Member] | Bank Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, additional borrowing capacity					50,000,000
Bank credit facilities	425,000,000	[1]	325,000,000	[1]		325,000,000	[1]
Amount available at end of period	304,830,000	[2]				210,110,000	[2]
NJR [Member] | Bank Revolving Credit Facility [Member] | Notes Payable to Banks [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period	93,500,000					97,000,000
Weighted average interest rate at end of period	1.16%					1.00%
NJR [Member] | Bank Term Loan [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period	0					100,000,000
Weighted average interest rate at end of period	0.00%					0.74%
Amount available at end of period	100,000,000					0
Bank term loan	100,000,000	[3]				100,000,000	[3]
NJR [Member] | Bank Letter of Credit Facility [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	0	[3],[4]				10,000,000	[3],[4]
NJNG [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	731,000					266,000
NJNG [Member] | Bank Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	250,000,000	[1]				250,000,000	[1]
Line of credit facility, maximum borrowing capacity, incremental increase	15,000,000
Line of credit facility, maximum borrowing capacity, maximum increase	50,000,000
Amount available at end of period	168,269,000	[5]				81,400,000	[5]
NJNG [Member] | Bank Revolving Credit Facility [Member] | Commercial Paper [Member]
Line of Credit Facility [Line Items]
Amount outstanding at end of period	81,000,000					168,600,000
Weighted average interest rate at end of period	0.11%					0.13%
NJNG [Member] | Bank Credit Facility Dedicated to EDA Bonds [Member]
Line of Credit Facility [Line Items]
Bank credit facilities	$ 100,000,000	[1],[4]				$ 100,000,000	[1],[4]

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

[2] Letters of credit outstanding total $26.7 million and $17.9 million as of June 30, 2014 and September 30, 2013, respectively, which reduces amount available by the same amount.

[3] Uncommitted, expired on June 5, 2014.

[4] There were no borrowings outstanding as of June 30, 2014 and September 30, 2013, respectively.

[5] Letters of credit outstanding total $731,000 and $266,000 as of June 30, 2014 and September 30, 2013, respectively, which reduces the amount available by the same amount.