COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	9 Months Ended
	Jun. 30, 2013
Long-term Purchase Commitment [Line Items]
Current charges recoverable through BGSS	$ 99,700,000
Natural Gas Purchases [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
2013	247,632,000
2014	126,175,000
2015	31,225,000
2016	16,800,000
2017	0
Thereafter	0
Natural Gas Purchases [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
2013	37,843,000
2014	94,047,000
2015	103,080,000
2016	8,755,000
2017	113,000
Thereafter	0
Storage Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
2013	9,615,000
2014	26,098,000
2015	12,005,000
2016	7,114,000
2017	5,035,000
Thereafter	7,318,000
Storage Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
2013	7,061,000
2014	28,208,000
2015	21,283,000
2016	11,956,000
2017	9,990,000
Thereafter	23,247,000
Pipeline Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
2013	18,557,000
2014	31,851,000
2015	18,133,000
2016	9,576,000
2017	8,225,000
Thereafter	9,756,000
Pipeline Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
2013	15,504,000
2014	75,442,000
2015	41,596,000
2016	34,558,000
2017	32,753,000
Thereafter	221,838,000
Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2013	336,212,000	[1]
2014	381,821,000	[1]
2015	227,322,000	[1]
2016	88,759,000	[1]
2017	56,116,000	[1]
Thereafter	262,159,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
2013	275,804,000
2014	184,124,000
2015	61,363,000
2016	33,490,000
2017	13,260,000
Thereafter	17,074,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
2013	60,408,000
2014	197,697,000
2015	165,959,000
2016	55,269,000
2017	42,856,000
Thereafter	$ 245,085,000

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