DERIVATIVE INSTRUMENTS - OFFSETTING OF ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Sep. 30, 2014
NJRES [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	[1]	$ 42,043	$ 67,270
Offsetting Derivative Instruments, Derivative assets	[2]	(29,774)	(63,375)
Financial Collateral Received/Pledged, Derivative assets	[3]	0	0
Net Amounts, Derivative assets	[4]	12,269	3,895
Amounts Presented in Balance Sheets, Derivative liabilities	[1]	40,703	84,323
Offsetting Derivative Instruments, Derivative liabilities	[2]	(29,775)	(63,902)
Financial Collateral Received/Pledged, Derivative liabilities	[3]	(1,200)	(2,614)
Net Amounts, Derivative liabilities	[4]	9,728	17,807
NJRES [Member] | Physical Forward Commodity Contracts [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	[1]	11,965	15,426
Offsetting Derivative Instruments, Derivative assets	[2]	(5,972)	(11,531)
Financial Collateral Received/Pledged, Derivative assets	[3]	0	0
Net Amounts, Derivative assets	[4]	5,993	3,895
Amounts Presented in Balance Sheets, Derivative liabilities	[1]	16,900	30,910
Offsetting Derivative Instruments, Derivative liabilities	[2]	(5,972)	(12,058)
Financial Collateral Received/Pledged, Derivative liabilities	[3]	(1,200)	(1,200)
Net Amounts, Derivative liabilities	[4]	9,728	17,652
NJRES [Member] | Financial Commodity Contracts [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	[1]	30,078	51,844
Offsetting Derivative Instruments, Derivative assets	[2]	(23,802)	(51,844)
Financial Collateral Received/Pledged, Derivative assets	[3]	0	0
Net Amounts, Derivative assets	[4]	6,276	0
Amounts Presented in Balance Sheets, Derivative liabilities	[1]	23,803	53,258
Offsetting Derivative Instruments, Derivative liabilities	[2]	(23,803)	(51,844)
Financial Collateral Received/Pledged, Derivative liabilities	[3]	0	(1,414)
Net Amounts, Derivative liabilities	[4]	0	0
NJRES [Member] | Foreign Currency Contract [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative liabilities	[1]		155
Offsetting Derivative Instruments, Derivative liabilities	[2]		0
Financial Collateral Received/Pledged, Derivative liabilities	[3]		0
Net Amounts, Derivative liabilities	[4]		155
NJNG [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	[1]	4,225
Offsetting Derivative Instruments, Derivative assets	[2]	(1,320)
Financial Collateral Received/Pledged, Derivative assets	[3]	0
Net Amounts, Derivative assets	[4]	2,905
NJNG [Member] | Financial Commodity Contracts [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	[1]	1,320	2,607
Offsetting Derivative Instruments, Derivative assets	[2]	(1,320)	(2,230)
Financial Collateral Received/Pledged, Derivative assets	[3]	0	(377)
Net Amounts, Derivative assets	[4]	0	0
Amounts Presented in Balance Sheets, Derivative liabilities	[1]	14,701	2,230
Offsetting Derivative Instruments, Derivative liabilities	[2]	(1,320)	(2,230)
Financial Collateral Received/Pledged, Derivative liabilities	[3]	(13,381)	0
Net Amounts, Derivative liabilities	[4]	0	$ 0
NJNG [Member] | Interest Rate Contracts [Member]
Offsetting Assets and Liabilities [Line Items]
Amounts Presented in Balance Sheets, Derivative assets	[1]	2,905
Offsetting Derivative Instruments, Derivative assets	[2]	0
Financial Collateral Received/Pledged, Derivative assets	[3]	0
Net Amounts, Derivative assets	[4]	$ 2,905

[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.