FAIR VALUE OPTION - Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets	$ 20,586,262	$ 22,032,021
Liabilities	12,645,610	15,586,216
Private Equity
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets	3,012	3,744
Credit
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets	4,958,922	4,381,519
Investments of Consolidated CFEs
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets	13,293,505	15,573,203
Real Assets
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets	321,644	343,820
Equity Method - Other
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets	1,744,961	1,384,739
Other Investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets	264,218	344,996
Debt Obligations of Consolidated CFEs
Fair Value, Option, Quantitative Disclosures [Line Items]
Liabilities	$ 12,645,610	$ 15,586,216