COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	3 Months Ended
	Dec. 31, 2014
Long-term Purchase Commitment [Line Items]
Current charges recoverable through BGSS	$ 62,300,000
Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	467,601,000	[1]
2016	278,480,000	[1]
2017	97,053,000	[1]
2018	117,291,000	[1]
2019	106,448,000	[1]
Thereafter	884,359,000	[1]
NJRES [Member] | Natural Gas Purchases [Member]
Long-term Purchase Commitment [Line Items]
2015	272,131,000
2016	106,975,000
2017	5,673,000
2018	0
2019	0
Thereafter	0
NJRES [Member] | Storage Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	21,019,000
2016	15,503,000
2017	4,274,000
2018	2,520,000
2019	1,782,000
Thereafter	2,598,000
NJRES [Member] | Pipeline Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	61,654,000
2016	50,559,000
2017	23,246,000
2018	15,079,000
2019	7,212,000
Thereafter	7,838,000
NJRES [Member] | Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	354,804,000
2016	173,037,000
2017	33,193,000
2018	17,599,000
2019	8,994,000
Thereafter	10,436,000
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 [Member]
Long-term Purchase Commitment [Line Items]
2015	50,539,000
2016	3,923,000
2017	113,000
2018	0
2019	0
Thereafter	0
NJNG [Member] | Storage Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	21,143,000
2016	24,957,000
2017	17,910,000
2018	12,811,000
2019	9,299,000
Thereafter	4,649,000
NJNG [Member] | Pipeline Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	41,115,000
2016	76,563,000
2017	45,837,000
2018	86,881,000
2019	88,155,000
Thereafter	869,274,000
NJNG [Member] | Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	112,797,000
2016	105,443,000
2017	63,860,000
2018	99,692,000
2019	97,454,000
Thereafter	$ 873,923,000

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