SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CUSTOMER ACCOUNTS RECEIVABLE (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Sep. 30, 2014
accounts receivable by subsidiary [Line Items]
Billed	$ 331,378		$ 189,970
Receivable by Subsidiary, percentage	100.00%		100.00%
Unbilled revenues	42,864		7,231
NJRES [Member]
accounts receivable by subsidiary [Line Items]
Billed	171,563		142,566
Receivable by Subsidiary, percentage	52.00%		75.00%
NJNG [Member]
accounts receivable by subsidiary [Line Items]
Billed	153,642	[1]	41,281	[1]
Receivable by Subsidiary, percentage	46.00%		22.00%
NJRCEV [Member]
accounts receivable by subsidiary [Line Items]
Billed	1,127		594
Receivable by Subsidiary, percentage	0.00%		0.00%
NJRHS and Other [Member]
accounts receivable by subsidiary [Line Items]
Billed	$ 5,046		$ 5,529
Receivable by Subsidiary, percentage	2.00%		3.00%

[1] Does not include unbilled revenues of $42.9 million and $7.2 million as of March 31, 2015 and September 30, 2014, respectively.