BUSINESS COMBINATIONS - Narrative (Details) - USD ($) $ in Thousands			3 Months Ended		4 Months Ended	9 Months Ended
	Jul. 01, 2021	Jun. 02, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Asset Acquisition [Line Items]
Acquisition and merger-related expense		$ 4,900
Goodwill		$ 417,700	$ 787,750		$ 787,750	$ 787,750		$ 371,047
Total revenues					54,000
Net income					$ 26,800
Landmark Acquisition
Asset Acquisition [Line Items]
Business combination equity interest in acquiree, percentage		100.00%
Business combination, consideration transferred		$ 1,103,469
Goodwill		417,665
Total revenues			948,719	$ 527,105		2,966,540	$ 1,214,989
Net income			$ 87,542	$ 37,570		$ 257,361	$ 41,263
Landmark Acquisition | Management contracts
Asset Acquisition [Line Items]
Acquisition and merger-related expense		$ 425,900
Acquired finite lived intangible assets useful life		7 years 4 months 24 days
Landmark Acquisition | Client relationships
Asset Acquisition [Line Items]
Acquisition and merger-related expense		$ 197,200
Acquired finite lived intangible assets useful life		11 years 9 months 18 days
Landmark Acquisition | Trade name
Asset Acquisition [Line Items]
Acquisition and merger-related expense		$ 86,200
Landmark Partners XVI - GP
Asset Acquisition [Line Items]
Business combination equity interest in acquiree, percentage		60.00%
Black Creek Acquisition
Asset Acquisition [Line Items]
Business combination equity interest in acquiree, percentage	100.00%
Bargain purchase gain	$ 42,300
Black Creek Acquisition | Management contracts
Asset Acquisition [Line Items]
Acquisition and merger-related expense	$ 576,200
Acquired finite lived intangible assets useful life	6 years 1 month 6 days
Black Creek Acquisition | Client relationships
Asset Acquisition [Line Items]
Acquisition and merger-related expense	$ 7,200
Acquired finite lived intangible assets useful life	12 years