REVENUES - Revenues Disaggregated by Fund Structure (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 205,190	$ 241,227	$ 785,088	$ 791,831
Management Fees
Disaggregation of Revenue [Line Items]
Revenues	179,761	175,195	524,798	538,706
Closed-end
Disaggregation of Revenue [Line Items]
Revenues	120,462	112,415	345,091	353,225
Open-end
Disaggregation of Revenue [Line Items]
Revenues	29,990	34,942	90,480	109,051
Evergreen
Disaggregation of Revenue [Line Items]
Revenues	29,309	27,838	89,227	76,430
Incentive Income
Disaggregation of Revenue [Line Items]
Revenues	25,429	66,032	260,290	253,125
Closed-end
Disaggregation of Revenue [Line Items]
Revenues	25,335	65,661	257,778	249,447
Evergreen
Disaggregation of Revenue [Line Items]
Revenues	$ 94	$ 371	$ 2,512	$ 3,678