BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Unconsolidated Investments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) investment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Number of investments, fair value option | investment	31
Income from unconsolidated investments - performance fees | $	$ 36.3	$ 27.4	$ 8.8