COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2016 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Current charges recoverable through BGSS	$ 17,600
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	215,043	[1]
2017	461,391	[1]
2018	274,835	[1]
2019	214,293	[1]
2020	148,493	[1]
Thereafter	933,908	[1]
NJRES [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	178,267
2017	285,963
2018	142,306
2019	71,671
2020	9,181
Thereafter	11,123
NJRES [Member] | Natural Gas Purchases [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	139,097
2017	193,138
2018	104,064
2019	57,868
2020	0
Thereafter	0
NJRES [Member] | Storage Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	11,303
2017	32,816
2018	14,582
2019	8,104
2020	6,258
Thereafter	7,308
NJRES [Member] | Pipeline Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	27,867
2017	60,009
2018	23,660
2019	5,699
2020	2,923
Thereafter	$ 3,815
NJRES [Member] | Minimum [Member]
Long-term Purchase Commitment [Line Items]
Storage and pipeline capacity, contract term	1 year
NJRES [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Storage and pipeline capacity, contract term	10 years
NJNG [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	$ 36,776
2017	175,428
2018	132,529
2019	142,622
2020	139,312
Thereafter	922,785
NJNG [Member] | Natural Gas Purchases [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	19,170
2017	80,193
2018	39,226
2019	41,658
2020	43,611
Thereafter	104,378
NJNG [Member] | Storage Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	7,255
2017	29,131
2018	22,255
2019	12,834
2020	5,776
Thereafter	0
NJNG [Member] | Pipeline Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	10,351
2017	66,104
2018	71,048
2019	88,130
2020	89,925
Thereafter	$ 818,407

[1] Does not include amounts related to intercompany asset management agreements between NJRES and NJNG.