COMMITMENTS AND CONTINGENT LIABILITIES, SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	9 Months Ended
	Jun. 30, 2011
Long-term Purchase Commitment [Line Items]
Current Charges Recoverable Through BGSS	$ 105,000,000
NJNG [Member] | 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	64,922,000
NJNG [Member] | 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	114,945,000
NJNG [Member] | 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	106,886,000
NJNG [Member] | 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	95,974,000
NJNG [Member] | 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	50,181,000
NJNG [Member] | 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	273,001,000
NJRES [Member] | 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	291,853,000
NJRES [Member] | 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	421,340,000
NJRES [Member] | 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	108,568,000
NJRES [Member] | 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	20,174,000
NJRES [Member] | 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	14,402,000
NJRES [Member] | 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	33,356,000
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	356,775,000
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	536,285,000
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	215,454,000
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	116,148,000
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	64,583,000
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	306,357,000
NJNG [Member] | Natural Gas Purchases [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	40,809,000
NJNG [Member] | Natural Gas Purchases [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	6,928,000
NJNG [Member] | Natural Gas Purchases [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
NJNG [Member] | Natural Gas Purchases [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
NJNG [Member] | Natural Gas Purchases [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
NJNG [Member] | Natural Gas Purchases [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
NJRES [Member] | Natural Gas Purchases [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	268,965,000
NJRES [Member] | Natural Gas Purchases [Member] | More than One and within Two Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	347,341,000
NJRES [Member] | Natural Gas Purchases [Member] | More than Two and within Three Years from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	69,619,000
NJRES [Member] | Natural Gas Purchases [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
NJRES [Member] | Natural Gas Purchases [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
NJRES [Member] | Natural Gas Purchases [Member] | More than Five Years from Balance Sheet Date and Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	0
NJNG [Member] | Storage Demand Fees [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	7,804,000
NJNG [Member] | Storage 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	31,208,000
NJNG [Member] | Storage 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	29,920,000
NJNG [Member] | Storage 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	24,153,000
NJNG [Member] | Storage 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	14,999,000
NJNG [Member] | Storage 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	44,340,000
NJRES [Member] | Storage Demand Fees [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	10,046,000
NJRES [Member] | Storage 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	31,140,000
NJRES [Member] | Storage 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	17,399,000
NJRES [Member] | Storage 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	11,494,000
NJRES [Member] | Storage 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	7,207,000
NJRES [Member] | Storage 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	11,924,000
NJNG [Member] | Pipeline Demand Fees [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	16,309,000
NJNG [Member] | Pipeline 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	76,809,000
NJNG [Member] | Pipeline 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	76,966,000
NJNG [Member] | Pipeline 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	71,821,000
NJNG [Member] | Pipeline 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	35,182,000
NJNG [Member] | Pipeline 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	228,661,000
NJRES [Member] | Pipeline Demand Fees [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	12,842,000
NJRES [Member] | Pipeline 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	42,859,000
NJRES [Member] | Pipeline 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	21,550,000
NJRES [Member] | Pipeline 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	8,680,000
NJRES [Member] | Pipeline 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	7,195,000
NJRES [Member] | Pipeline 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	$ 21,432,000