DERIVATIVE INSTRUMENTS, OFFSETTING OF ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands		Sep. 30, 2016		Sep. 30, 2015
NJRES
Derivative assets:
Amounts Presented on the Balance Sheets	[1]	$ 34,076		$ 44,870
Offsetting Derivative Instruments	[2]	(20,783)		(15,060)
Financial Collateral Received/Pledged	[3]	(6,904)		3,841
Net Amounts	[4]	6,389		33,651
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	58,740		23,004
Offsetting Derivative Instruments	[2]	(20,783)		(15,059)
Financial Collateral Received/Pledged	[3]	(26,691)		(1,200)
Net Amounts	[4]	11,266		6,745
NJRES | Physical commodity contracts
Derivative assets:
Amounts Presented on the Balance Sheets	[1]	9,981		6,562
Offsetting Derivative Instruments	[2]	(2,837)		(1,326)
Financial Collateral Received/Pledged	[3]	(755)		0
Net Amounts	[4]	6,389		5,236
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	12,872		9,271
Offsetting Derivative Instruments	[2]	(2,837)		(1,326)
Financial Collateral Received/Pledged	[3]	1,200		(1,200)
Net Amounts	[4]	11,235		6,745
NJRES | Financial commodity contracts
Derivative assets:
Amounts Presented on the Balance Sheets	[1]	24,094		38,308
Offsetting Derivative Instruments	[2]	(17,945)		(13,734)
Financial Collateral Received/Pledged	[3]	(6,149)		3,841
Net Amounts	[4]	0		28,415
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	45,836		13,733
Offsetting Derivative Instruments	[2]	(17,945)		(13,733)
Financial Collateral Received/Pledged	[3]	(27,891)		0
Net Amounts	[4]	0		0
NJRES | Foreign currency contracts
Derivative assets:
Amounts Presented on the Balance Sheets		1
Offsetting Derivative Instruments		(1)
Financial Collateral Received/Pledged		0
Net Amounts		0
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	32
Offsetting Derivative Instruments	[2]	(1)
Financial Collateral Received/Pledged	[3]	0
Net Amounts	[4]	31
NJNG
Derivative assets:
Amounts Presented on the Balance Sheets	[1]	1,115
Offsetting Derivative Instruments	[2]	(911)
Financial Collateral Received/Pledged	[3]	0
Net Amounts	[4]	204
Derivative liabilities:
Amounts Presented in Balance Sheets		27,592	[1]	15,316
Offsetting Derivative Instruments		(911)	[2]	(207)
Financial Collateral Received/Pledged		(2,485)	[3]	(10,881)
Net Amounts		24,196	[4]	4,228
NJNG | Physical commodity contracts
Derivative assets:
Amounts Presented on the Balance Sheets		235
Offsetting Derivative Instruments		(31)
Financial Collateral Received/Pledged		0
Net Amounts		204
Derivative liabilities:
Amounts Presented in Balance Sheets		1,154
Offsetting Derivative Instruments		(31)
Financial Collateral Received/Pledged		0
Net Amounts		1,123
NJNG | Financial commodity contracts
Derivative assets:
Amounts Presented on the Balance Sheets	[1]	880		207
Offsetting Derivative Instruments	[2]	(880)		(207)
Financial Collateral Received/Pledged	[3]	0		0
Net Amounts	[4]	0		0
Derivative liabilities:
Amounts Presented in Balance Sheets	[1]	3,365		11,088
Offsetting Derivative Instruments	[2]	(880)		(207)
Financial Collateral Received/Pledged	[3]	(2,485)		(10,881)
Net Amounts	[4]	0		0
NJNG | Interest rate contracts
Derivative assets:
Amounts Presented on the Balance Sheets	[1]	0
Offsetting Derivative Instruments	[2]	0
Financial Collateral Received/Pledged	[3]	0
Net Amounts	[4]	0
Derivative liabilities:
Amounts Presented in Balance Sheets		23,073	[1]	4,228
Offsetting Derivative Instruments		0	[2]	0
Financial Collateral Received/Pledged		0	[3]	0
Net Amounts		$ 23,073	[4]	$ 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 FCMs 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.