SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CUSTOMER ACCOUNTS RECEIVABLE (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Sep. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed		$ 148,822	$ 155,273
Receivable by subsidiary, percentage		100.00%	100.00%
Unbilled revenues		$ 27,144	$ 6,372
NJRES [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed		$ 75,691	$ 107,461
Receivable by subsidiary, percentage		51.00%	69.00%
NJNG [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	[1]	$ 67,080	$ 41,130
Receivable by subsidiary, percentage	[1]	45.00%	26.00%
NJRCEV [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed		$ 1,975	$ 1,084
Receivable by subsidiary, percentage		1.00%	1.00%
NJRHS and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed		$ 4,076	$ 5,598
Receivable by subsidiary, percentage		3.00%	4.00%

[1] Does not include unbilled revenues of $27.1 million and $6.4 million as of March 31, 2016 and September 30, 2015, respectively.