FAIR VALUE, DEBT (Details) (Fair Value, Inputs, Level 2 [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
NJNG [Member] | Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 379,845	$ 329,845
NJNG [Member] | Fair Market Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	397,175	364,394
NJR [Member] | Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	150,000	150,000
NJR [Member] | Fair Market Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 159,343	$ 165,662