DERIVATIVE INSTRUMENTS - OFFSETTING OF ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Sep. 30, 2015
NJRES [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	$ 61,899	$ 44,870
Offsetting Derivative Instruments	[2]	(13,813)	(15,060)
Financial Collateral Received/Pledged	[3]	(26,136)	3,841
Net Amounts	[4]	21,950	33,651
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	38,805	23,004
Offsetting Derivative Instruments	[2]	(13,813)	(15,059)
Financial Collateral Received/Pledged	[3]	(3,966)	(1,200)
Net Amounts	[4]	21,026	6,745
NJRES [Member] | Physical Forward Commodity Contracts [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	12,889	6,562
Offsetting Derivative Instruments	[2]	(809)	(1,326)
Financial Collateral Received/Pledged	[3]	(1,000)	0
Net Amounts	[4]	11,080	5,236
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	22,983	9,271
Offsetting Derivative Instruments	[2]	(809)	(1,326)
Financial Collateral Received/Pledged	[3]	(1,200)	(1,200)
Net Amounts	[4]	20,974	6,745
NJRES [Member] | Financial Commodity Contracts [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	49,010	38,308
Offsetting Derivative Instruments	[2]	(13,004)	(13,734)
Financial Collateral Received/Pledged	[3]	(25,136)	3,841
Net Amounts	[4]	10,870	28,415
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	15,770	13,733
Offsetting Derivative Instruments	[2]	(13,004)	(13,733)
Financial Collateral Received/Pledged	[3]	(2,766)	0
Net Amounts	[4]	0	0
NJRES [Member] | Foreign Currency Contracts [Member]
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	52
Offsetting Derivative Instruments	[2]	0
Financial Collateral Received/Pledged	[3]	0
Net Amounts	[4]	52
NJNG [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	820
Offsetting Derivative Instruments	[2]	(820)
Financial Collateral Received/Pledged	[3]	0
Net Amounts	[4]	0
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	15,680	15,316
Offsetting Derivative Instruments	[2]	(820)	(207)
Financial Collateral Received/Pledged	[3]	(12,999)	(10,881)
Net Amounts	[4]	1,861	4,228
NJNG [Member] | Financial Commodity Contracts [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	820	207
Offsetting Derivative Instruments	[2]	(820)	(207)
Financial Collateral Received/Pledged	[3]	0	0
Net Amounts	[4]	0	0
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	13,819	11,088
Offsetting Derivative Instruments	[2]	(820)	(207)
Financial Collateral Received/Pledged	[3]	(12,999)	(10,881)
Net Amounts	[4]	0	0
NJNG [Member] | Interest Rate Contracts [Member]
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	1,861	4,228
Offsetting Derivative Instruments	[2]	0	0
Financial Collateral Received/Pledged	[3]	0	0
Net Amounts	[4]	$ 1,861	$ 4,228

[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.