INVESTMENTS - Net Gains (Losses) from Investment Activities of Consolidated Funds (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Gain (Loss) on Investments [Line Items]
Net realized gain (loss) on consolidated funds’ investments	$ 3,392	$ (1,436)	$ 1,755	$ 8,647
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	3,662	10,231	56,793	(15,742)
Consolidated Funds \| Not Designated as Hedging Instrument
Gain (Loss) on Investments [Line Items]
Net realized gain (loss) on consolidated funds’ investments	3,392	(1,436)	1,755	8,647
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	3,662	10,231	56,793	(15,742)
Consolidated Funds \| Investments and other financial instruments \| Not Designated as Hedging Instrument
Gain (Loss) on Investments [Line Items]
Net realized gain (loss) on consolidated funds’ investments	3,839	1,267	6,075	13,589
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	2,012	56,490	10,941	83,913
Consolidated Funds \| CLO Liabilities \| Not Designated as Hedging Instrument
Gain (Loss) on Investments [Line Items]
Net realized gain (loss) on consolidated funds’ investments	0	0	0	0
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	1,595	(46,553)	44,943	(98,927)
Consolidated Funds \| Foreign-currency forward contracts \| Not Designated as Hedging Instrument
Gain (Loss) on Investments [Line Items]
Net realized gain (loss) on consolidated funds’ investments	(555)	368	(945)	(132)
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	200	(465)	(210)	(8)
Consolidated Funds \| Total-return and interest-rate swaps \| Not Designated as Hedging Instrument
Gain (Loss) on Investments [Line Items]
Net realized gain (loss) on consolidated funds’ investments	70	(2,395)	(1,398)	(3,285)
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	(185)	683	813	(713)
Consolidated Funds \| Options and futures \| Not Designated as Hedging Instrument
Gain (Loss) on Investments [Line Items]
Net realized gain (loss) on consolidated funds’ investments	38	(676)	(1,977)	(1,525)
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	$ 40	$ 76	$ 306	$ (7)

The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.3(a))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 325
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031664&loc=d3e22529-158502

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of investments, not including unrealized gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, held at each balance sheet date and included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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