DERIVATIVES AND HEDGING - Impact of Derivatives Held by Consolidated Funds on Income (Details) - Not Designated as Hedging Instrument - Consolidated Funds - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivatives, Fair Value [Line Items]
Net Realized Gain (Loss) on Investments	$ (447)	$ (2,703)	$ (4,320)	$ (4,942)
Net Change in Unrealized Appreciation (Depreciation) on Investments	55	294	909	(728)
Foreign-currency forward contracts
Derivatives, Fair Value [Line Items]
Net Realized Gain (Loss) on Investments	(555)	368	(945)	(132)
Net Change in Unrealized Appreciation (Depreciation) on Investments	200	(465)	(210)	(8)
Total-return and interest-rate swaps
Derivatives, Fair Value [Line Items]
Net Realized Gain (Loss) on Investments	70	(2,395)	(1,398)	(3,285)
Net Change in Unrealized Appreciation (Depreciation) on Investments	(185)	683	813	(713)
Options and futures
Derivatives, Fair Value [Line Items]
Net Realized Gain (Loss) on Investments	38	(676)	(1,977)	(1,525)
Net Change in Unrealized Appreciation (Depreciation) on Investments	$ 40	$ 76	$ 306	$ (7)