REVENUES - Revenues Disaggregated by Fund Structure (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 313,483	$ 213,283	$ 579,898	$ 550,604
Management Fees
Disaggregation of Revenue [Line Items]
Revenues	175,103	178,096	345,037	363,511
Closed-end
Disaggregation of Revenue [Line Items]
Revenues	115,254	117,423	224,629	240,810
Open-end
Disaggregation of Revenue [Line Items]
Revenues	28,949	36,557	60,490	74,109
Evergreen
Disaggregation of Revenue [Line Items]
Revenues	30,900	24,116	59,918	48,592
Incentive Income
Disaggregation of Revenue [Line Items]
Revenues	138,380	35,187	234,861	187,093
Closed-end
Disaggregation of Revenue [Line Items]
Revenues	135,962	31,880	232,443	183,786
Evergreen
Disaggregation of Revenue [Line Items]
Revenues	$ 2,418	$ 3,307	$ 2,418	$ 3,307