COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	6 Months Ended
	Mar. 31, 2013
Long-term Purchase Commitment [Line Items]
Current charges recoverable through BGSS	$ 96,000,000
Natural Gas Purchases [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	431,244,000
Purchase Obligation, Due in Second Year	99,374,000
Purchase Obligation, Due in Third Year	31,484,000
Purchase Obligation, Due in Fourth Year	16,420,000
Other Commitment, Due in Fifth Year	0
Long-term purchase commitment, amount	0
Natural Gas Purchases [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	72,604,000
Purchase Obligation, Due in Second Year	110,195,000
Purchase Obligation, Due in Third Year	109,158,000
Purchase Obligation, Due in Fourth Year	9,041,000
Other Commitment, Due in Fifth Year	113,000
Long-term purchase commitment, amount	0
Storage Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	16,655,000
Purchase Obligation, Due in Second Year	23,326,000
Purchase Obligation, Due in Third Year	12,016,000
Purchase Obligation, Due in Fourth Year	7,114,000
Other Commitment, Due in Fifth Year	5,035,000
Long-term purchase commitment, amount	7,318,000
Storage Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	14,134,000
Purchase Obligation, Due in Second Year	25,398,000
Purchase Obligation, Due in Third Year	17,310,000
Purchase Obligation, Due in Fourth Year	11,956,000
Other Commitment, Due in Fifth Year	9,990,000
Long-term purchase commitment, amount	23,247,000
Pipeline Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	29,824,000
Purchase Obligation, Due in Second Year	25,644,000
Purchase Obligation, Due in Third Year	10,426,000
Purchase Obligation, Due in Fourth Year	8,801,000
Other Commitment, Due in Fifth Year	7,452,000
Long-term purchase commitment, amount	9,371,000
Pipeline Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	31,090,000
Purchase Obligation, Due in Second Year	74,586,000
Purchase Obligation, Due in Third Year	39,239,000
Purchase Obligation, Due in Fourth Year	34,558,000
Other Commitment, Due in Fifth Year	32,753,000
Long-term purchase commitment, amount	221,838,000
Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	595,551,000	[1]
Purchase Obligation, Due in Second Year	358,523,000	[1]
Purchase Obligation, Due in Third Year	219,633,000	[1]
Purchase Obligation, Due in Fourth Year	87,890,000	[1]
Other Commitment, Due in Fifth Year	55,343,000	[1]
Long-term purchase commitment, amount	261,774,000	[1]
Natural Gas Purchases and Future Demand Fees [Member] | NJRES [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	477,723,000
Purchase Obligation, Due in Second Year	148,344,000
Purchase Obligation, Due in Third Year	53,926,000
Purchase Obligation, Due in Fourth Year	32,335,000
Other Commitment, Due in Fifth Year	12,487,000
Long-term purchase commitment, amount	16,689,000
Natural Gas Purchases and Future Demand Fees [Member] | NJNG [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation, Due in Next Twelve Months	117,828,000
Purchase Obligation, Due in Second Year	210,179,000
Purchase Obligation, Due in Third Year	165,707,000
Purchase Obligation, Due in Fourth Year	55,555,000
Other Commitment, Due in Fifth Year	42,856,000
Long-term purchase commitment, amount	$ 245,085,000

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