COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	6 Months Ended
	Mar. 31, 2014
Long-term Purchase Commitment [Line Items]
Current charges recoverable through BGSS	$ 95,100,000
Natural Gas Purchases [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
2014	320,608,000
2015	99,106,000
2016	15,452,000
2017	0
2018	0
Thereafter	0
Natural Gas Purchases [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
2014	55,132,000
2015	107,920,000
2016	6,522,000
2017	113,000
2018	0
Thereafter	0
Storage Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
2014	15,571,000
2015	20,773,000
2016	9,931,000
2017	5,425,000
2018	3,318,000
Thereafter	4,000,000
Storage Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
2014	12,995,000
2015	20,611,000
2016	13,285,000
2017	10,883,000
2018	9,299,000
Thereafter	13,948,000
Pipeline Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
2014	35,978,000
2015	43,174,000
2016	33,561,000
2017	18,307,000
2018	12,548,000
Thereafter	7,175,000
Pipeline Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
2014	32,139,000
2015	74,142,000
2016	43,312,000
2017	34,247,000
2018	33,978,000
Thereafter	194,675,000
Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2014	472,423,000	[1]
2015	365,726,000	[1]
2016	122,063,000	[1]
2017	68,975,000	[1]
2018	59,143,000	[1]
Thereafter	219,798,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
2014	372,157,000
2015	163,053,000
2016	58,944,000
2017	23,732,000
2018	15,866,000
Thereafter	11,175,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
2014	100,266,000
2015	202,673,000
2016	63,119,000
2017	45,243,000
2018	43,277,000
Thereafter	$ 208,623,000

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