DERIVATIVE INSTRUMENTS - OFFSETTING OF ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016
NJRES
Derivative assets:
Amounts Presented in Balance Sheets	$ 38,763	$ 34,076
Offsetting Derivative Instruments	(34,372)	(20,783)
Financial Collateral Received/Pledged	(200)	(6,904)
Net Amounts	4,191	6,389
Derivative liabilities:
Amounts Presented in Balance Sheets	91,910	58,740
Offsetting Derivative Instruments	(34,371)	(20,783)
Financial Collateral Received/Pledged	(53,555)	(26,691)
Net Amounts	3,984	11,266
NJRES | Physical commodity contracts
Derivative assets:
Amounts Presented in Balance Sheets	7,669	9,981
Offsetting Derivative Instruments	(3,278)	(2,837)
Financial Collateral Received/Pledged	(200)	(755)
Net Amounts	4,191	6,389
Derivative liabilities:
Amounts Presented in Balance Sheets	7,171	12,872
Offsetting Derivative Instruments	(3,278)	(2,837)
Financial Collateral Received/Pledged	0	1,200
Net Amounts	3,893	11,235
NJRES | Financial commodity contracts
Derivative assets:
Amounts Presented in Balance Sheets	31,094	24,094
Offsetting Derivative Instruments	(31,094)	(17,945)
Financial Collateral Received/Pledged	0	(6,149)
Net Amounts	0	0
Derivative liabilities:
Amounts Presented in Balance Sheets	84,648	45,836
Offsetting Derivative Instruments	(31,093)	(17,945)
Financial Collateral Received/Pledged	(53,555)	(27,891)
Net Amounts	0	0
NJRES | Foreign currency contracts
Derivative assets:
Amounts Presented in Balance Sheets		1
Offsetting Derivative Instruments		(1)
Financial Collateral Received/Pledged		0
Net Amounts		0
Derivative liabilities:
Amounts Presented in Balance Sheets	91	32
Offsetting Derivative Instruments	0	(1)
Financial Collateral Received/Pledged	0	0
Net Amounts	91	31
NJNG
Derivative assets:
Amounts Presented in Balance Sheets	15,112	1,115
Offsetting Derivative Instruments	(2,923)	(911)
Financial Collateral Received/Pledged	(4,205)	0
Net Amounts	7,984	204
Derivative liabilities:
Amounts Presented in Balance Sheets	5,697	27,592
Offsetting Derivative Instruments	(2,923)	(911)
Financial Collateral Received/Pledged	0	(2,485)
Net Amounts	2,774	24,196
NJNG | Physical commodity contracts
Derivative assets:
Amounts Presented in Balance Sheets	1,181	235
Offsetting Derivative Instruments	(4)	(31)
Financial Collateral Received/Pledged	0	0
Net Amounts	1,177	204
Derivative liabilities:
Amounts Presented in Balance Sheets	76	1,154
Offsetting Derivative Instruments	(4)	(31)
Financial Collateral Received/Pledged	0	0
Net Amounts	72	1,123
NJNG | Financial commodity contracts
Derivative assets:
Amounts Presented in Balance Sheets	13,931	880
Offsetting Derivative Instruments	(2,919)	(880)
Financial Collateral Received/Pledged	(4,205)	0
Net Amounts	6,807	0
Derivative liabilities:
Amounts Presented in Balance Sheets	2,919	3,365
Offsetting Derivative Instruments	(2,919)	(880)
Financial Collateral Received/Pledged	0	(2,485)
Net Amounts	0	0
NJNG | Interest rate contracts
Derivative liabilities:
Amounts Presented in Balance Sheets	2,702	23,073
Offsetting Derivative Instruments	0	0
Financial Collateral Received/Pledged	0	0
Net Amounts	$ 2,702	$ 23,073