COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Oct. 31, 2017
Contingencies And Commitments [Line Items]
Accrued incentives (fund level)	$ 1,293,366		$ 1,293,366		$ 1,434,458
Compensation expense related to accrued incentives (fund level)	675,029		675,029		754,903
Contingent consideration	36,100		36,100
Contingent consideration, fair value	6,700		6,700		6,700
Contingent consideration income (expense)	(200)	$ 7,100	100	$ 9,600
Capital commitments	370,500		370,500		385,800
Consolidated Funds
Contingencies And Commitments [Line Items]
Aggregate potential credit and investment commitments	39,000		39,000		$ 13,800
BDC Acquisition
Contingencies And Commitments [Line Items]
Indemnification asset	$ 32,000		$ 32,000			$ 56,200