COMMITMENTS AND CONTINGENT LIABILITIES, SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	12 Months Ended
	Sep. 30, 2011
Long-term Purchase Commitment [Line Items]
Current Charges Recoverable Through BGSS	$ 107,000,000
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	126,471,000
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	107,273,000
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	95,794,000
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	50,151,000
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	42,695,000
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	234,701,000
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	620,586,000
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	195,747,000
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	33,071,000
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	18,492,000
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	13,097,000
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	25,303,000
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	747,057,000	[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	303,020,000	[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	128,865,000	[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	68,643,000	[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	55,792,000	[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	260,004,000	[1]
NJNG [Member] | Natural Gas Purchases [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	19,128,000
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	0
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	536,331,000
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	149,972,000
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	6,587,000
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	31,171,000
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	29,882,000
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	24,128,000
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	14,992,000
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	11,088,000
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	33,245,000
NJRES [Member] | Storage Demand Fees [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	35,554,000
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	19,023,000
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	12,624,000
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	7,725,000
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	4,000,000
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	7,875,000
NJNG [Member] | Pipeline Demand Fees [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	76,172,000
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	77,391,000
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	71,666,000
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	35,159,000
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	31,607,000
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	201,456,000
NJRES [Member] | Pipeline Demand Fees [Member] | Three Months from Balance Sheet Date [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	48,701,000
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	26,752,000
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	13,860,000
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	10,767,000
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	9,097,000
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	$ 17,428,000

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