NET INVESTMENT INCOME (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
Realized gains (losses)									$ 87,618	$ (113,836)	$ 22,227
Change in unrealized gains and losses									(41,444)	209,993	(265,401)
Investment related foreign exchange gains (losses)									5,292	3,094	6,225
Interest and dividend income, net of withholding taxes									25,510	23,915	15,313
Interest, dividend and other expenses									(23,937)	(22,334)	(31,092)
Investment advisor compensation									(19,863)	(24,543)	(19,246)
Net investment income (loss)	$ (16,214)	$ 63,976	$ (39,149)	$ 11,618	$ 52,857	$ 32,945	$ (38,054)	$ 28,435	$ 20,231	$ 76,183	$ (281,924)
Net investment gain (loss) as a percentage									1.50%	7.20%	(20.20%)
Net Investment Income (Loss) [Member]
Investment related foreign exchange gains (losses)									$ 7,653	$ (2,988)	$ 3,725