COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) (USD $)	6 Months Ended
	Mar. 31, 2015
Long-term Purchase Commitment [Line Items]
Current charges recoverable through BGSS	$ 40,600,000
Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	328,820,000	[1]
2016	387,471,000	[1]
2017	192,133,000	[1]
2018	169,977,000	[1]
2019	157,329,000	[1]
Thereafter	1,054,802,000	[1]
NJRES [Member] | Natural Gas Purchases [Member]
Long-term Purchase Commitment [Line Items]
2015	197,232,000
2016	130,025,000
2017	5,059,000
2018	0
2019	0
Thereafter	0
NJRES [Member] | Storage Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	13,262,000
2016	20,746,000
2017	7,509,000
2018	4,123,000
2019	2,306,000
Thereafter	3,383,000
NJRES [Member] | Pipeline Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	46,374,000
2016	56,531,000
2017	29,550,000
2018	15,082,000
2019	7,212,000
Thereafter	7,838,000
NJRES [Member] | Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	256,868,000
2016	207,302,000
2017	42,118,000
2018	19,205,000
2019	9,518,000
Thereafter	11,221,000
NJRES [Member] | Minimum [Member]
Long-term Purchase Commitment [Line Items]
Storage and pipeline capacity, contract term	1 year
NJRES [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Storage and pipeline capacity, contract term	10 years
NJNG [Member] | Natural Gas Purchases [Member]
Long-term Purchase Commitment [Line Items]
2015	31,306,000
2016	74,991,000
2017	79,203,000
2018	49,459,000
2019	50,325,000
Thereafter	169,489,000
NJNG [Member] | Storage Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	14,406,000
2016	25,762,000
2017	20,524,000
2018	14,398,000
2019	9,299,000
Thereafter	4,649,000
NJNG [Member] | Pipeline Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	26,240,000
2016	79,416,000
2017	50,288,000
2018	86,915,000
2019	88,187,000
Thereafter	869,443,000
NJNG [Member] | Natural Gas Purchases and Future Demand Fees [Member]
Long-term Purchase Commitment [Line Items]
2015	71,952,000
2016	180,169,000
2017	150,015,000
2018	150,772,000
2019	147,811,000
Thereafter	$ 1,043,581,000

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