COMMITMENTS AND CONTINGENT LIABILITIES, SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	9 Months Ended
	Jun. 30, 2012
Long-term Purchase Commitment [Line Items]
Current Charges Recoverable Through BGSS	$ 101,200,000
Natural Gas Purchases and Future Demand Fees [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	254,938,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	393,348,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	147,118,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	74,010,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	58,852,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	264,845,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	219,588,000
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	285,550,000
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	48,956,000
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	22,912,000
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	16,189,000
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	29,785,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	35,350,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	107,798,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	98,162,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	51,098,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	42,663,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	235,060,000
Natural Gas Purchases [Member] | NJRES [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	190,416,000
Natural Gas Purchases [Member] | NJRES [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	213,773,000
Natural Gas Purchases [Member] | NJRES [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	8,735,000
Natural Gas Purchases [Member] | NJRES [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
Natural Gas Purchases [Member] | NJRES [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
Natural Gas Purchases [Member] | NJRES [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
Natural Gas Purchases [Member] | NJNG [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	14,085,000
Natural Gas Purchases [Member] | NJNG [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	1,191,000
Natural Gas Purchases [Member] | NJNG [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
Natural Gas Purchases [Member] | NJNG [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
Natural Gas Purchases [Member] | NJNG [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
Natural Gas Purchases [Member] | NJNG [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
Storage Demand Fees [Member] | NJRES [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	11,503,000
Storage Demand Fees [Member] | NJRES [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	30,740,000
Storage Demand Fees [Member] | NJRES [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	18,634,000
Storage Demand Fees [Member] | NJRES [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	12,016,000
Storage Demand Fees [Member] | NJRES [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	7,106,000
Storage Demand Fees [Member] | NJRES [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	12,353,000
Storage Demand Fees [Member] | NJNG [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	7,783,000
Storage Demand Fees [Member] | NJNG [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	29,834,000
Storage Demand Fees [Member] | NJNG [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	25,015,000
Storage Demand Fees [Member] | NJNG [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	15,888,000
Storage Demand Fees [Member] | NJNG [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	11,088,000
Storage Demand Fees [Member] | NJNG [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	33,245,000
Pipeline Demand Fees [Member] | NJRES [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	17,669,000
Pipeline Demand Fees [Member] | NJRES [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	41,037,000
Pipeline Demand Fees [Member] | NJRES [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	21,587,000
Pipeline Demand Fees [Member] | NJRES [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	10,896,000
Pipeline Demand Fees [Member] | NJRES [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	9,083,000
Pipeline Demand Fees [Member] | NJRES [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	17,432,000
Pipeline Demand Fees [Member] | NJNG [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	13,482,000
Pipeline Demand Fees [Member] | NJNG [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	76,773,000
Pipeline Demand Fees [Member] | NJNG [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	73,147,000
Pipeline Demand Fees [Member] | NJNG [Member] | More than Three and within Four Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	35,210,000
Pipeline Demand Fees [Member] | NJNG [Member] | More than Four and within Five Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	31,575,000
Pipeline Demand Fees [Member] | NJNG [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	$ 201,815,000

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