COMMITMENTS AND CONTINGENT LIABILITIES, SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	6 Months Ended
	Mar. 31, 2012
Long-term Purchase Commitment [Line Items]
Current Charges Recoverable Through BGSS	$ 96,000,000
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	380,570,000	[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	363,255,000	[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	145,835,000	[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	74,278,000	[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	58,979,000	[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	264,863,000	[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	317,863,000
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	255,313,000
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	47,562,000
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	23,177,000
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	16,313,000
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	29,780,000
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	62,707,000
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	107,942,000
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	98,273,000
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	51,101,000
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	42,666,000
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	235,083,000
Natural Gas Purchases [Member] | NJRES [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	264,023,000
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	181,858,000
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	6,555,000
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	19,877,000
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	1,096,000
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	21,136,000
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	31,625,000
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	18,838,000
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	12,286,000
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	7,236,000
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	15,666,000
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	30,070,000
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	25,123,000
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	32,704,000
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	41,830,000
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	22,169,000
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	10,891,000
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	9,077,000
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	17,427,000
Pipeline Demand Fees [Member] | NJNG [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	27,164,000
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	76,776,000
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	73,150,000
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	35,213,000
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	31,578,000
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	$ 201,838,000

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