REVENUES - Revenues Disaggregated by Fund Structure (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 266,415	$ 337,321
Management Fees
Disaggregation of Revenue [Line Items]
Revenues	169,934	185,415
Closed-end
Disaggregation of Revenue [Line Items]
Revenues	109,375	123,387
Open-end
Disaggregation of Revenue [Line Items]
Revenues	31,541	37,552
Evergreen
Disaggregation of Revenue [Line Items]
Revenues	29,018	24,476
Incentive Income
Disaggregation of Revenue [Line Items]
Revenues	96,481	151,906
Closed-end
Disaggregation of Revenue [Line Items]
Revenues	96,481	151,906
Evergreen
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration