SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CUSTOMER ACCOUNTS RECEIVABLE (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Sep. 30, 2014
accounts receivable by subsidiary [Line Items]
Billed		$ 197,086	$ 189,970
Receivable by Subsidiary, percentage		100.00%	100.00%
Unbilled revenues		$ 6,707	$ 7,231
NJRES [Member]
accounts receivable by subsidiary [Line Items]
Billed		$ 114,531	$ 142,566
Receivable by Subsidiary, percentage		58.00%	75.00%
NJNG [Member]
accounts receivable by subsidiary [Line Items]
Billed	[1]	$ 76,716	$ 41,281
Receivable by Subsidiary, percentage		39.00%	22.00%
NJRCEV [Member]
accounts receivable by subsidiary [Line Items]
Billed		$ 898	$ 594
Receivable by Subsidiary, percentage		0.00%	0.00%
NJRHS and Other [Member]
accounts receivable by subsidiary [Line Items]
Billed		$ 4,941	$ 5,529
Receivable by Subsidiary, percentage		3.00%	3.00%

[1] Does not include unbilled revenues of $6.7 million and $7.2 million as of June 30, 2015 and September 30, 2014, respectively.