FAIR VALUE - Consolidated Funds Summary of Valuation Techniques and Quantitative Information (Details) - Consolidated Funds $ in Thousands	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Real estate securities	$ 57,080	$ 0
Total Level III investments	6,939,504	6,531,385
Level III
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Total Level III investments	226,689	325,922
Level III | Recent transaction price
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Real estate securities	57,080
Level III | Communication services | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments		20,746
Level III | Communication services | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments		2,416
Level III | Consumer discretionary | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	8,621
Level III | Consumer discretionary | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	6,203
Level III | Financials | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	12,023	108,277
Level III | Financials | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	4,393	3,608
Level III | Health care | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	25,321	37,724
Level III | Health care | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	2,012	2,550
Level III | Real estate | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	15,067	79,562
Level III | Real estate | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	3,563	4,570
Level III | Other | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	33,494	38,959
Level III | Other | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments	14,010	17,943
Level III | Other | Recent transaction price
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments		5,078
Level III | Equity Investment | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments	2,493	2,099
Level III | Equity Investment | Market approach (comparable companies)
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments		$ 2,390
Level III | Equity Investment | Recent transaction price
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments	$ 39,883
Discount rate | Level III | Communication services | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs		0.12
Discount rate | Level III | Communication services | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs		0.14
Discount rate | Level III | Communication services | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs		0.13
Discount rate | Level III | Consumer discretionary | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.10
Discount rate | Level III | Consumer discretionary | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.14
Discount rate | Level III | Consumer discretionary | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.12
Discount rate | Level III | Financials | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.09	0.09
Discount rate | Level III | Financials | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.12	0.15
Discount rate | Level III | Financials | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.11	0.14
Discount rate | Level III | Health care | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.10	0.10
Discount rate | Level III | Health care | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.17	0.16
Discount rate | Level III | Health care | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.12	0.14
Discount rate | Level III | Real estate | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.10	0.12
Discount rate | Level III | Real estate | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.12	0.23
Discount rate | Level III | Real estate | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.11	0.14
Discount rate | Level III | Other | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.08	0.08
Discount rate | Level III | Other | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.15	0.15
Discount rate | Level III | Other | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Credit-oriented investments, significant unobservable inputs	0.13	0.13
Discount rate | Level III | Equity Investment | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	0.10	0.10
Discount rate | Level III | Equity Investment | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	0.15	0.30
Discount rate | Level III | Equity Investment | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	0.11	0.12
Earnings multiple | Level III | Equity Investment | Market approach (comparable companies)
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments	$ 2,166
Earnings multiple | Level III | Equity Investment | Market approach (comparable companies) | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	4	4
Earnings multiple | Level III | Equity Investment | Market approach (comparable companies) | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	8	10
Earnings multiple | Level III | Equity Investment | Market approach (comparable companies) | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	6	7
Revenue multiple | Level III | Equity Investment | Market approach (comparable companies)
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments	$ 360
Revenue multiple | Level III | Equity Investment | Market approach (comparable companies) | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	2
Revenue multiple | Level III | Equity Investment | Market approach (comparable companies) | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	4
Revenue multiple | Level III | Equity Investment | Market approach (comparable companies) | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Equity investments, significant unobservable inputs	3