INVESTMENTS - Equity-method Investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Schedule of Equity Method Investments [Line Items]
Revenues / investment income	$ 339,302	$ 457,262	$ 1,231,263	$ 934,753
Interest expense	(60,041)	(65,385)	(130,898)	(132,615)
Other expenses	(119,402)	(215,921)	(481,302)	(417,357)
Net realized and unrealized gain on investments	115,770	815,438	1,120,917	1,345,799
Net income	$ 275,629	$ 991,394	$ 1,739,980	$ 1,730,580
Maximum
Schedule of Equity Method Investments [Line Items]
Ownership percentage	2.50%		2.50%
Double Line
Schedule of Equity Method Investments [Line Items]
Ownership percentage	20.00%		20.00%