INVESTMENTS - Investment income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Equity Method Investments [Line Items]
Other investments, at fair value	$ (6,285)	$ 14,059	$ (4,649)	$ 9,439
Total investment income	49,106	41,000	99,557	70,447
Funds
Schedule of Equity Method Investments [Line Items]
Equity-method investments investment income (loss)	36,562	10,259	69,483	29,219
Companies
Schedule of Equity Method Investments [Line Items]
Equity-method investments investment income (loss)	$ 18,829	$ 16,682	$ 34,723	$ 31,789