DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Sep. 30, 2015	Jun. 01, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Benchmark interest rate			3.26%
Notional amount of foreign currency derivatives			$ 125,000
Fair Value
Derivative assets, current	$ 54,803	$ 40,743
Derivative liabilities, current	53,735	32,791
Derivative assets, noncurrent	1,174	4,334
Derivative liabilities, noncurrent	13,913	5,529
Derivative assets	55,977	45,087
Derivative liabilities	67,648	38,330
Not Designated as Hedging Instrument [Member]
Fair Value
Derivative assets	55,970	45,087
Derivative liabilities	67,648	38,330
NJRES [Member] | Designated as Hedging Instrument [Member] | Foreign Currency Contracts [Member]
Fair Value
Derivative assets, current	7	0
Derivative liabilities, current	0	0
Derivative assets	7	0
Derivative liabilities	0	0
NJRES [Member] | Not Designated as Hedging Instrument [Member] | Physical Commodity Contracts [Member]
Fair Value
Derivative assets, current	5,245	4,854
Derivative liabilities, current	8,892	9,281
Derivative assets, noncurrent	914	1,718
Derivative liabilities, noncurrent	158	0
NJRES [Member] | Not Designated as Hedging Instrument [Member] | Financial Commodity Contracts [Member]
Fair Value
Derivative assets, current	47,241	35,682
Derivative liabilities, current	23,739	13,347
Derivative assets, noncurrent	260	2,626
Derivative liabilities, noncurrent	823	386
NJNG [Member] | Interest Rate Contracts [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional amount of foreign currency derivatives	125,000	125,000
NJNG [Member] | Not Designated as Hedging Instrument [Member] | Physical Commodity Contracts [Member]
Fair Value
Derivative assets, current	58	0
Derivative liabilities, current	90	0
NJNG [Member] | Not Designated as Hedging Instrument [Member] | Financial Commodity Contracts [Member]
Fair Value
Derivative assets, current	2,252	207
Derivative liabilities, current	21,014	10,163
Derivative assets, noncurrent	0	0
Derivative liabilities, noncurrent	0	925
NJNG [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member]
Fair Value
Derivative assets, noncurrent	0	0
Derivative liabilities, noncurrent	12,932	$ 4,228
First Mortgage [Member] | Series Ll [Member] | NJNG [Member]
Derivatives, Fair Value [Line Items]
Debt issued	$ 125,000
Interest rate, stated percentage	5.60%