COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2015 USD ($)
Long-term Purchase Commitment [Line Items]
Current charges recoverable through BGSS	$ 58,500
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	407,622	[1]
2017	316,349	[1]
2018	258,655	[1]
2019	205,778	[1]
2020	146,504	[1]
Thereafter	889,219	[1]
NJRES [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	307,161
2017	159,210
2018	109,425
2019	63,497
2020	7,925
Thereafter	7,164
NJRES [Member] | Natural Gas Purchases [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	212,469
2017	94,896
2018	84,187
2019	51,029
2020	0
Thereafter	0
NJRES [Member] | Storage Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	20,288
2017	13,290
2018	8,565
2019	4,960
2020	3,672
Thereafter	3,270
NJRES [Member] | Pipeline Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	74,404
2017	51,024
2018	16,673
2019	7,508
2020	4,253
Thereafter	$ 3,894
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	$ 100,461
2017	157,139
2018	149,230
2019	142,281
2020	138,579
Thereafter	882,055
NJNG [Member] | Natural Gas Purchases [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	41,962
2017	63,953
2018	39,885
2019	40,976
2020	43,775
Thereafter	98,948
NJNG [Member] | Storage Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	21,815
2017	25,328
2018	15,871
2019	11,079
2020	5,345
Thereafter	0
NJNG [Member] | Pipeline Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	36,684
2017	67,858
2018	93,474
2019	90,226
2020	89,459
Thereafter	$ 783,107

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