DERIVATIVE INSTRUMENTS - OFFSETTING OF ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Sep. 30, 2014
NJRES [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	$ 64,247	[1]	$ 67,270	[1]
Offsetting Derivative Instruments, Derivative assets	(54,001)	[2]	(63,375)	[2]
Financial Collateral Received/Pledged, Derivative assets	0	[3]	0	[3]
Net Amounts, Derivative assets	10,246	[4]	3,895	[4]
Amounts Presented in Balance Sheets, Derivative liabilities	62,579	[1]	84,323	[1]
Offsetting Derivative Instruments, Derivative liabilities	(54,001)	[2]	(63,902)	[2]
Financial Collateral Received/Pledged, Derivative liabilities	(1,200)	[3]	(2,614)	[3]
Net Amounts, Derivative liabilities	7,378	[4]	17,807	[4]
NJRES [Member] | Physical Forward Commodity Contracts [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	11,076	[1]	15,426	[1]
Offsetting Derivative Instruments, Derivative assets	(2,961)	[2]	(11,531)	[2]
Financial Collateral Received/Pledged, Derivative assets	0	[3]	0	[3]
Net Amounts, Derivative assets	8,115	[4]	3,895	[4]
Amounts Presented in Balance Sheets, Derivative liabilities	11,521	[1]	30,910	[1]
Offsetting Derivative Instruments, Derivative liabilities	(2,961)	[2]	(12,058)	[2]
Financial Collateral Received/Pledged, Derivative liabilities	(1,200)	[3]	(1,200)	[3]
Net Amounts, Derivative liabilities	7,360	[4]	17,652	[4]
NJRES [Member] | Financial Commodity Contracts [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	53,171	[1]	51,844	[1]
Offsetting Derivative Instruments, Derivative assets	(51,040)	[2]	(51,844)	[2]
Financial Collateral Received/Pledged, Derivative assets	0	[3]	0	[3]
Net Amounts, Derivative assets	2,131	[4]	0	[4]
Amounts Presented in Balance Sheets, Derivative liabilities	51,040	[1]	53,258	[1]
Offsetting Derivative Instruments, Derivative liabilities	(51,040)	[2]	(51,844)	[2]
Financial Collateral Received/Pledged, Derivative liabilities	0	[3]	(1,414)	[3]
Net Amounts, Derivative liabilities	0	[4]	0	[4]
NJRES [Member] | Foreign Currency Contract [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative liabilities	18	[1]	155	[1]
Offsetting Derivative Instruments, Derivative liabilities	0	[2]	0	[2]
Financial Collateral Received/Pledged, Derivative liabilities	0	[3]	0	[3]
Net Amounts, Derivative liabilities	18	[4]	155	[4]
NJNG [Member] | Financial Commodity Contracts [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	907	[1]	2,607	[1]
Offsetting Derivative Instruments, Derivative assets	(907)	[2]	(2,230)	[2]
Financial Collateral Received/Pledged, Derivative assets	0	[3]	(377)	[3]
Net Amounts, Derivative assets	0	[4]	0	[4]
Amounts Presented in Balance Sheets, Derivative liabilities	25,645	[1]	2,230	[1]
Offsetting Derivative Instruments, Derivative liabilities	(907)	[2]	(2,230)	[2]
Financial Collateral Received/Pledged, Derivative liabilities	(24,738)	[3]	0	[3]
Net Amounts, Derivative liabilities	$ 0	[4]	$ 0	[4]

[1] Derivative assets and liabilities are presented on a gross basis in the balance sheet as the Company does not elect balance sheet offsetting under ASC 210-20.

[2] Offsetting derivative instruments include: transactions with NAESB netting election, transactions held by FCM's with net margining and transactions with ISDA netting.

[3] Financial collateral includes cash balances at FCMs as well as cash received from or pledged to other counterparties.

[4] Net amounts represent presentation of derivative assets and liabilities if the Company were to elect balance sheet offsetting under ASC 210-20.