REVENUES FROM CONTRACTS WITH CUSTOMERS (Summary of Revenue from Contracts with Customers Disaggregated by Type of Customer) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 7,910	$ 12,228	$ 26,076	$ 38,459
Management fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,275	9,607	19,807	30,728
Other revenues and fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,635	2,621	6,269	7,731
Permanent Capital Vehicles
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,237	8,668	17,281	26,471
Permanent Capital Vehicles | Management fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,045	6,593	12,855	21,144
Permanent Capital Vehicles | Other revenues and fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,192	2,075	4,426	5,327
Long-dated Private Funds
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,097	1,616	3,633	5,185
Long-dated Private Funds | Management fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,097	1,616	3,633	5,185
Long-dated Private Funds | Other revenues and fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
SMAs
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,133	1,398	3,319	4,399
SMAs | Management fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,133	1,398	3,319	4,399
SMAs | Other revenues and fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	443	546	1,843	2,404
Other | Management fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Other revenues and fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 443	$ 546	$ 1,843	$ 2,404