DERIVATIVE INSTRUMENTS, BALANCE SHEET RELATED DISCLOSURES (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015	Jun. 01, 2015
Derivatives, Fair Value [Line Items]
Fixed treasury rate			3.26%
Notional amount of foreign currency derivatives			$ 125,000
Asset Derivatives, current	$ 29,964	$ 40,743
Asset Derivatives, noncurrent	5,227	4,334
Asset Derivatives	35,191	45,087
Liability Derivatives, current	61,080	32,791
Liability Derivatives, noncurrent	25,252	5,529
Liability Derivatives	86,332	38,330
Physical commodity contracts | NJNG | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current	235	0
Liability Derivatives, current	1,154	0
Physical commodity contracts | NJRES | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current	5,994	4,854
Asset Derivatives, noncurrent	3,987	1,718
Liability Derivatives, current	11,660	9,281
Liability Derivatives, noncurrent	1,212	0
Financial commodity contracts | NJNG | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current	805	207
Asset Derivatives, noncurrent	75	0
Liability Derivatives, current	2,979	10,163
Liability Derivatives, noncurrent	386	925
Financial commodity contracts | NJRES | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current	22,929	35,682
Asset Derivatives, noncurrent	1,165	2,626
Liability Derivatives, current	45,255	13,347
Liability Derivatives, noncurrent	581	386
Interest rate contracts | NJNG | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, noncurrent	0	0
Liability Derivatives, noncurrent	23,073	4,228
Foreign currency contracts
Derivatives, Fair Value [Line Items]
Notional amount of foreign currency derivatives	3,600
Foreign currency contracts | NJRES | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current	1	0
Liability Derivatives, current	32	0
First mortgage bonds: | Series LL | NJNG
Derivatives, Fair Value [Line Items]
Long-term debt	$ 125,000	$ 125,000
Stated interest rate	5.60%