REVENUES - Revenues Disaggregated by Fund Structure (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 928,987	$ 1,386,079	$ 1,469,767
Closed-end
Disaggregation of Revenue [Line Items]
Total revenues	345,026	466,319	504,727
Open-end
Disaggregation of Revenue [Line Items]
Total revenues	93,401	142,013	160,961
Evergreen
Disaggregation of Revenue [Line Items]
Total revenues	89,227	103,688	60,726
Sub-advisory
Disaggregation of Revenue [Line Items]
Total revenues	51,209	0	0
Management Fees
Disaggregation of Revenue [Line Items]
Total revenues	578,863	712,020	726,414
Closed-end
Disaggregation of Revenue [Line Items]
Total revenues	334,287	651,021	701,065
Evergreen
Disaggregation of Revenue [Line Items]
Total revenues	15,837	23,038	42,288
Incentive Income
Disaggregation of Revenue [Line Items]
Total revenues	$ 350,124	$ 674,059	$ 743,353