NET INVESTMENT INCOME (LOSS) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Investment Income [Abstract]
Realized gains (losses)									$ (14,150,000)	$ (236,887,000)	$ 87,618,000
Change in unrealized gains and losses									8,380,000	(32,597,000)	(41,444,000)
Investment related foreign exchange gains (losses)									20,000	938,000	(7,653,000)
Interest and dividend income, net of withholding taxes									16,059,000	35,468,000	25,510,000
Interest, dividend and other expenses									(4,798,000)	(17,987,000)	(23,937,000)
Income (loss) from equity method investment									700,000	(247,000)	0
Investment advisor compensation on joint venture									0	(11,221,000)	(19,863,000)
Net investment related income (loss)									6,211,000	(262,533,000)	20,231,000
Income (loss) from investment in related party investment fund	$ (5,714,000)	$ 6,609,000	$ 14,405,000	$ 30,756,000	$ (50,548,000)	$ (10,025,000)	$ 0	$ 0	46,056,000	(60,573,000)	0
Total net investment related income (loss)									$ 52,267,000	$ (323,106,000)	$ 20,231,000
Net investment gain (loss) as a percentage									9.30%	(30.30%)	1.50%
Net increase (decrease) in provision									$ 5,988,000	$ 0	$ 0