GOODWILL AND INTANGIBLE ASSETS - Carrying Value of Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Finite-lived intangible assets, net
Finite-lived intangible assets	$ 882,317	$ 247,077
Foreign currency translation	1,530	3,093
Total finite-lived intangible assets	883,847	250,170
Less: accumulated amortization	(85,157)	(28,082)
Finite-lived intangible assets, net	798,690	222,088
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	654,000	0
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Intangible assets, net	1,452,690	222,088
Management contracts
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	567,800	0
Trade name
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 86,200	0
Management contracts
Finite-lived intangible assets, net
Weighted average amortization period	6 years 6 months
Finite-lived intangible assets	$ 641,737	210,857
Client relationships
Finite-lived intangible assets, net
Weighted average amortization period	11 years 2 months 12 days
Finite-lived intangible assets	$ 229,501	25,141
Trade name
Finite-lived intangible assets, net
Weighted average amortization period	8 years 8 months 12 days
Finite-lived intangible assets	$ 11,079	$ 11,079