SEGMENT REPORTING - Expenses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total Segment Expenses	$ 636,703	$ 530,247	$ 629,728	$ 540,014	$ 452,816	$ 511,117	$ 423,218	$ 308,323	$ 2,336,692	$ 1,695,474	$ 1,871,225
Segment Reconciling Items
Segment Reporting Information [Line Items]
Less: Equity based compensation									334,821	264,890	261,579
Less: Reimbursable expenses and placement fees									181,839	148,483	103,307
Less: Operating expenses relating to consolidated funds, CFEs and other entities									82,888	104,339	65,012
Less: Expenses incurred by oil & gas producing entities									46,411	70,312	153,611
Less: Intangible amortization									17,821	6,647	49,766
Less: Other									46,692	32,228	46,038
Reportable segments
Segment Reporting Information [Line Items]
Total Segment Expenses									$ 1,626,220	$ 1,068,575	$ 1,191,912