COMMITMENTS AND CONTINGENT LIABILITIES, SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	3 Months Ended
	Dec. 31, 2011
Long-term Purchase Commitment [Line Items]
Current Charges Recoverable Through BGSS	$ 90,000,000
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	498,685,000	[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	308,660,000	[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	133,764,000	[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	70,124,000	[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	56,013,000	[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	260,389,000	[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	419,726,000
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	202,310,000
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	36,902,000
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	19,918,000
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	13,347,000
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	25,304,000
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	78,959,000
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	106,350,000
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	96,862,000
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	50,206,000
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	235,085,000
Natural Gas Purchases [Member] | NJRES [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	340,289,000
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	148,449,000
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	6,216,000
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	14,017,000
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	0
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	26,296,000
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	21,940,000
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	15,081,000
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	9,008,000
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	4,250,000
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	7,875,000
Storage Demand Fees [Member] | NJNG [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	23,465,000
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	30,072,000
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	24,227,000
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	14,992,000
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	53,141,000
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	31,921,000
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	15,605,000
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	10,910,000
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	9,097,000
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	17,429,000
Pipeline Demand Fees [Member] | NJNG [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	41,477,000
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	76,278,000
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	72,635,000
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	35,214,000
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	$ 201,840,000

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