DERIVATIVE INSTRUMENTS, BALANCE SHEET RELATED DISCLOSURES (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Jun. 01, 2015	Sep. 30, 2014
Derivatives, Fair Value [Line Items]
Fixed treasury rate		3.26%
Notional amount of foreign currency derivatives		$ 125,000
Asset Derivatives, Current	$ 40,743		$ 64,223
Liability Derivatives, Current	32,791		79,863
Asset Derivatives, Noncurrent	4,334		5,654
Liability Derivatives, Noncurrent	5,529		6,690
Asset Derivatives	45,087		69,877
Liability Derivatives	38,330		86,553
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	45,087		69,877
Liability Derivatives	38,330		86,398
Foreign Currency Contracts [Member] | NJRES [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Current	0		0
Liability Derivatives, Current	0		155
Asset Derivatives, Noncurrent	0		0
Liability Derivatives, Noncurrent	0		0
Asset Derivatives	0		0
Liability Derivatives	0		155
Financial Commodity Contracts [Member] | NJRES [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Current	35,682		46,307
Liability Derivatives, Current	13,347		46,725
Asset Derivatives, Noncurrent	2,626		5,537
Liability Derivatives, Noncurrent	386		6,533
Financial Commodity Contracts [Member] | NJNG [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Current	207		2,525
Liability Derivatives, Current	10,163		2,205
Asset Derivatives, Noncurrent	0		82
Liability Derivatives, Noncurrent	925		25
Interest Rate Contracts [Member] | NJNG [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Current	0		0
Liability Derivatives, Current	4,228		0
Physical Forward Commodity Contracts [Member] | NJRES [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Current	4,854		15,391
Liability Derivatives, Current	9,281		30,778
Asset Derivatives, Noncurrent	1,718		35
Liability Derivatives, Noncurrent	0		132
Treasury Lock [Member]
Derivatives, Fair Value [Line Items]
Notional amount of foreign currency derivatives	125,000
First Mortgage Bonds [Member] | Series LL [Member] | NJNG [Member]
Derivatives, Fair Value [Line Items]
Long-term debt	$ 125,000		$ 125,000
Stated interest rate	5.60%