SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fees and Other (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounting Policies [Abstract]
Management Fees	$ 187,727	$ 161,182
Transaction Fees	158,653	243,658
Monitoring Fees	17,586	13,504
Fee Credits	(29,053)	(88,078)
Incentive Fees	13,805	273
Expense Reimbursements	20,211	23,265
Oil and Gas Revenue	14,507	17,273
Consulting Fees	10,958	9,102
Total Fees and Other	394,394	380,179
Carried Interest	62,747	335,773
Less: General partner capital interest - unconsolidated funds	15,465	51,803
Total Capital Allocation-Based Income	78,212	387,576
Total Revenues	$ 472,606	767,755
Fees and Commissions [Line Items]
Gross management fees as a percentage of committed capital, low end of range	1.00%
Gross management fees as a percentage of committed capital, high end of range	2.00%
Maximum length of investment period	6 years
Percentage used to derive management fees for separately managed accounts, low end of range	0.50%
Percentage used to derive management fees for separately managed accounts, high end of range	2.00%
Asset Management Fees Earned From Credit Funds And Other Investment Vehicles, Percentage, Low End of Range	0.33%
Asset Management Fees Earned From Credit Funds And Other Investment Vehicles, Percentage, High End of Range	1.75%
Incentive fee, low end of range (as a percent)	5.00%
Incentive fee, high end of range (as a percent)	20.00%
Measurement period (in years)	1 year
Reportable segments
Accounting Policies [Abstract]
Fee Credits	$ (43,774)	(89,017)
Incentive Fees	202,555	206,204
Total Fees and Other	382,186	375,522
Total Revenues	$ 727,538	$ 1,022,698
Minimum
Fees and Commissions [Line Items]
Gross management fees as a percentage of capital	0.75%
Collateral Management Fee, Based on Annual Rate of Percentage of Collateral	0.40%
Minimum | Reportable segments
Fees and Commissions [Line Items]
Fee Credits as a percentage of monitoring and transaction fees net of fund-related expenses	80.00%
Maximum
Fees and Commissions [Line Items]
Gross management fees as a percentage of capital	1.25%
Collateral Management Fee, Based on Annual Rate of Percentage of Collateral	0.50%
Maximum | Reportable segments
Fees and Commissions [Line Items]
Fee Credits as a percentage of monitoring and transaction fees net of fund-related expenses	100.00%