COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2016 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Current charges recoverable through BGSS	$ 35,700
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	283,721	[1]
2017	374,972	[1]
2018	249,535	[1]
2019	202,950	[1]
2020	144,803	[1]
Thereafter	920,215	[1]
NJRES [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	224,799
2017	218,818
2018	119,396
2019	62,494
2020	7,856
Thereafter	7,837
NJRES [Member] | Natural Gas Purchases [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	151,898
2017	127,345
2018	82,142
2019	49,608
2020	0
Thereafter	0
NJRES [Member] | Storage Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	21,405
2017	31,439
2018	13,117
2019	6,728
2020	4,953
Thereafter	4,055
NJRES [Member] | Pipeline Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	51,496
2017	60,034
2018	24,137
2019	6,158
2020	2,903
Thereafter	$ 3,782
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	$ 58,922
2017	156,154
2018	130,139
2019	140,456
2020	136,947
Thereafter	912,378
NJNG [Member] | Natural Gas Purchases [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	23,178
2017	62,070
2018	39,166
2019	39,421
2020	41,226
Thereafter	93,884
NJNG [Member] | Storage Demand Fees [Member]
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2016	14,495
2017	29,099
2018	22,237
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	21,249
2017	64,985
2018	68,736
2019	88,201
2020	89,945
Thereafter	$ 818,494

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