SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Incentive income compensation vesting period	5 years
Cumulative effect adjustment	$ (1,612,550)	$ (1,581,018)		$ (1,702,169)	$ (2,129,756)	$ (2,423,663)	$ (2,487,717)
Adoption of new accounting guidance (ASU 2016-13)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustment				356
Retained Earnings (Accumulated Deficit)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustment	$ 39,267	$ 36,469		(51,534)	$ 0	$ (60,056)	$ (100,683)
Retained Earnings (Accumulated Deficit) | Adoption of new accounting guidance (ASU 2016-13)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustment				$ 220
Retained Earnings (Accumulated Deficit) | Accounting Standards Update 2016-13 | Adoption of new accounting guidance (ASU 2016-13)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustment			$ 400
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Withdrawal period	1 month
Minimum | Furniture, equipment and capitalized software
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated useful life (in years)	3 years
Minimum | Acquired intangibles
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Useful lives (in years)	7 years
Minimum | Contractual Rights to Earn Future Fee Income
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Useful lives (in years)	7 years
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Withdrawal period	3 years
Maximum | Furniture, equipment and capitalized software
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated useful life (in years)	5 years
Maximum | Acquired intangibles
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Useful lives (in years)	25 years
Maximum | Contractual Rights to Earn Future Fee Income
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Useful lives (in years)	25 years
Management fees | Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Management fees payment term (years)	10 years
Management fees | Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Management fees payment term (years)	11 years
Closed-end
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percentage of fund profits	20.00%
Preferred return on funds	8.00%
Evergreen
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percentage of fund profits	20.00%