FAIR VALUE OF FINANCIAL INSTRUMENTS (Schedule of Change in Fair Value of Investments Due to Change in Capitalization Rates) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017
Up 25 Basis Points [Member]
Investments in and Advances to Affiliates [Line Items]
Increase (decrease) in fair value of investments	$ (5.5)	$ (2.8)
Down 25 Basis Points [Member]
Investments in and Advances to Affiliates [Line Items]
Increase (decrease) in fair value of investments	6.0	3.1
Up 50 basis points [Member]
Investments in and Advances to Affiliates [Line Items]
Increase (decrease) in fair value of investments	(10.6)	(5.3)
Down 50 Basis Points [Member]
Investments in and Advances to Affiliates [Line Items]
Increase (decrease) in fair value of investments	$ 12.7	$ 6.4