DERIVATIVE INSTRUMENTS - OFFSETTING OF ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands		Jun. 30, 2016	Sep. 30, 2015
NJRES [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	$ 42,037	$ 44,870
Offsetting Derivative Instruments	[2]	(35,279)	(15,060)
Financial Collateral Received/Pledged	[3]	0	3,841
Net Amounts	[4]	6,758	33,651
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	77,954	23,004
Offsetting Derivative Instruments	[2]	(35,280)	(15,059)
Financial Collateral Received/Pledged	[3]	(36,156)	(1,200)
Net Amounts	[4]	6,518	6,745
NJRES [Member] | Physical Commodity Contracts [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	8,460	6,562
Offsetting Derivative Instruments	[2]	(3,431)	(1,326)
Financial Collateral Received/Pledged	[3]	0	0
Net Amounts	[4]	5,029	5,236
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	9,950	9,271
Offsetting Derivative Instruments	[2]	(3,432)	(1,326)
Financial Collateral Received/Pledged	[3]	0	(1,200)
Net Amounts	[4]	6,518	6,745
NJRES [Member] | Financial Commodity Contracts [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	33,577	38,308
Offsetting Derivative Instruments	[2]	(31,848)	(13,734)
Financial Collateral Received/Pledged	[3]	0	3,841
Net Amounts	[4]	1,729	28,415
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	68,004	13,733
Offsetting Derivative Instruments	[2]	(31,848)	(13,733)
Financial Collateral Received/Pledged	[3]	(36,156)	0
Net Amounts	[4]	0	0
NJNG [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	1,759
Offsetting Derivative Instruments	[2]	(1,631)
Financial Collateral Received/Pledged	[3]	0
Net Amounts	[4]	128
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	28,913	15,316
Offsetting Derivative Instruments	[2]	(1,631)	(207)
Financial Collateral Received/Pledged	[3]	(4,345)	(10,881)
Net Amounts	[4]	22,937	4,228
NJNG [Member] | Physical Commodity Contracts [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	130
Offsetting Derivative Instruments	[2]	(2)
Financial Collateral Received/Pledged	[3]	0
Net Amounts	[4]	128
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	307
Offsetting Derivative Instruments	[2]	(2)
Financial Collateral Received/Pledged	[3]	0
Net Amounts	[4]	305
NJNG [Member] | Financial Commodity Contracts [Member]
Derivative assets:
Amounts Presented in Balance Sheets	[1]	1,629	207
Offsetting Derivative Instruments	[2]	(1,629)	(207)
Financial Collateral Received/Pledged	[3]	0	0
Net Amounts	[4]	0	0
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	5,974	11,088
Offsetting Derivative Instruments	[2]	(1,629)	(207)
Financial Collateral Received/Pledged	[3]	(4,345)	(10,881)
Net Amounts	[4]	0	0
NJNG [Member] | Interest Rate Contracts [Member]
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	22,632	4,228
Offsetting Derivative Instruments	[2]	0	0
Financial Collateral Received/Pledged	[3]	0	0
Net Amounts	[4]	$ 22,632	$ 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.