SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ACCOUNTS RECEIVABLE BY SUBSIDIARY (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Sep. 30, 2013
accounts receivable by subsidiary [Line Items]
Billed	$ 276,409		$ 240,281
Receivable by Subsidiary, percentage	100.00%		100.00%
Unbilled revenues	7,464		7,429
NJRES [Member]
accounts receivable by subsidiary [Line Items]
Billed	186,014		194,263
Receivable by Subsidiary, percentage	67.00%		81.00%
NJNG [Member]
accounts receivable by subsidiary [Line Items]
Billed	85,579	[1]	43,045	[1]
Receivable by Subsidiary, percentage	31.00%		18.00%
NJRCEV [Member]
accounts receivable by subsidiary [Line Items]
Billed	480		293
Receivable by Subsidiary, percentage	0.00%		0.00%
NJRHS and Other [Member]
accounts receivable by subsidiary [Line Items]
Billed	$ 4,336		$ 2,680
Receivable by Subsidiary, percentage	2.00%		1.00%

[1] Does not include unbilled revenues of $7.5 million and $7.4 million as of June 30, 2014 and September 30, 2013, respectively.