DEBT, SCHEDULE OF LONG-TERM DEBT (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 15, 2015	Nov. 07, 2014	Sep. 30, 2014
Debt Instrument [Line Items]
Total long-term debt	$ 843,595			$ 598,209
NJNG [Member]
Debt Instrument [Line Items]
Less: Current maturities of long-term debt	(11,138)			(9,505)
Total long-term debt	618,595			473,209
NJNG [Member] | First Mortgage Bonds [Member] | Series II [Member]
Debt Instrument [Line Items]
Long-term debt	$ 10,300			10,300
Stated interest rate	4.50%
NJNG [Member] | First Mortgage Bonds [Member] | Series JJ [Member]
Debt Instrument [Line Items]
Long-term debt	$ 10,500			10,500
Stated interest rate	4.60%
NJNG [Member] | First Mortgage Bonds [Member] | Series KK [Member]
Debt Instrument [Line Items]
Long-term debt	$ 15,000			15,000
Stated interest rate	4.90%
NJNG [Member] | First Mortgage Bonds [Member] | Series LL [Member]
Debt Instrument [Line Items]
Long-term debt	$ 125,000			125,000
Stated interest rate	5.60%
NJNG [Member] | First Mortgage Bonds [Member] | Series MM [Member]
Debt Instrument [Line Items]
Long-term debt	$ 9,545			9,545
Interest rate term	Variable
NJNG [Member] | First Mortgage Bonds [Member] | Series NN [Member]
Debt Instrument [Line Items]
Long-term debt	$ 41,000			41,000
Interest rate term	Variable
NJNG [Member] | First Mortgage Bonds [Member] | Series OO [Member]
Debt Instrument [Line Items]
Long-term debt	$ 46,500			46,500
Interest rate term	Variable
NJNG [Member] | First Mortgage Bonds [Member] | Series PP [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000			50,000
Stated interest rate	3.15%
NJNG [Member] | First Mortgage Bonds [Member] | Series, QQ [Member]
Debt Instrument [Line Items]
Long-term debt	$ 70,000			70,000
Stated interest rate	3.58%
NJNG [Member] | First Mortgage Bonds [Member] | Series, RR [Member]
Debt Instrument [Line Items]
Long-term debt	$ 55,000			55,000
Stated interest rate	4.61%
NJNG [Member] | First Mortgage Bonds [Member] | Series, SS [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000			0
Stated interest rate	2.82%
NJNG [Member] | First Mortgage Bonds [Member] | Series, TT [Member]
Debt Instrument [Line Items]
Long-term debt	$ 100,000			0
Stated interest rate	3.66%
NJNG [Member] | Capital Lease Obligation [Member] | Capital lease obligation-Buildings [Member]
Debt Instrument [Line Items]
Long-term debt	$ 16,700			18,726
NJNG [Member] | Capital Lease Obligation [Member] | Capital lease obligation-Meters [Member]
Debt Instrument [Line Items]
Long-term debt	30,188			31,143
NJR [Member]
Debt Instrument [Line Items]
Less: Current maturities of long-term debt	0			(25,000)
Total long-term debt	225,000			125,000
NJR [Member] | Unsecured Senior Notes 6.05% [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000			50,000
Stated interest rate	6.05%
NJR [Member] | Unsecured Senior Notes 1.94% [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	$ 25,000		25,000
Stated interest rate	1.94%
NJR [Member] | Unsecured Senior Notes 2.51% [Member]
Debt Instrument [Line Items]
Long-term debt	$ 25,000			25,000
Stated interest rate	2.51%
NJR [Member] | Unsecured Senior Notes 3.25% [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000			50,000
Stated interest rate	3.25%
NJR [Member] | Unsecured Senior Notes 3.48% [Member]
Debt Instrument [Line Items]
Long-term debt	$ 100,000		$ 100,000	$ 0
Stated interest rate	3.48%		3.48%