SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fees and Other (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fees and Commissions [Line Items]
Fees and Other	$ 491,503	$ 355,418	$ 1,299,743	$ 1,116,382
Carried Interest	543,750	337,459	1,097,673	1,224,235
General Partner Capital Interest	94,413	56,775	176,476	192,590
Total Capital Allocation-Based Income	638,163	394,234	1,274,149	1,416,825
Total Revenues	$ 1,129,666	749,652	$ 2,573,892	2,533,207
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%		0.50%
Percentage used to derive management fees for separately managed accounts, high end of range	2.00%		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
Fees and Commissions [Line Items]
Fees and Other	$ 503,614	355,716	$ 1,283,548	1,096,398
Carried Interest	414,609	419,438	959,253	890,310
Total Revenues	$ 1,178,967	925,838	$ 2,786,763	2,353,051
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%		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%		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%
Management Fees
Fees and Commissions [Line Items]
Fees and Other	$ 188,866	178,942	$ 547,765	517,393
Management Fees | Reportable segments
Fees and Commissions [Line Items]
Fees and Other	276,595	232,954	789,630	670,807
Fee Credits
Fees and Commissions [Line Items]
Fees and Other	(73,904)	(70,641)	(137,804)	(207,396)
Fee Credits | Reportable segments
Fees and Commissions [Line Items]
Fees and Other	(82,187)	(70,747)	(178,982)	(211,148)
Transaction Fees
Fees and Commissions [Line Items]
Fees and Other	290,404	181,280	619,278	581,410
Transaction Fees | Reportable segments
Fees and Commissions [Line Items]
Fees and Other	289,030	179,167	609,800	578,667
Monitoring Fees
Fees and Commissions [Line Items]
Fees and Other	20,176	14,478	63,125	58,977
Monitoring Fees | Reportable segments
Fees and Commissions [Line Items]
Fees and Other	20,176	14,342	63,100	58,072
Incentive Fees
Fees and Commissions [Line Items]
Fees and Other	0	2,519	14,038	3,637
Expense Reimbursements
Fees and Commissions [Line Items]
Fees and Other	38,212	27,370	108,999	86,226
Oil and Gas Revenue
Fees and Commissions [Line Items]
Fees and Other	12,635	12,441	40,995	47,096
Consulting Fees
Fees and Commissions [Line Items]
Fees and Other	$ 15,114	$ 9,029	$ 43,347	$ 29,039