RELATED PARTY TRANSACTIONS (Details) - USD ($)	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	Dec. 31, 2014
Related Party Transaction [Line Items]
Redeemable non-controlling interest in related party joint venture	$ 7,169,000				$ 5,884,000				$ 7,169,000	$ 5,884,000	$ 12,265,000	$ 14,657,000
Nonredeemable Noncontrolling Interest	12,933,000				11,561,000				12,933,000	11,561,000	11,118,000	14,233,000
Noncontrolling Interest in Joint Ventures	20,102,000				17,445,000				20,102,000	17,445,000	23,382,000	$ 28,890,000
Change in non-controlling interest in related party joint venture	(202,000)	$ 1,078,000	$ (550,000)	$ 252,000	856,000	$ 981,000	$ (791,000)	$ 773,000	578,000	1,819,000	(5,508,000)
Debt instruments, trading, at fair value	7,180,000				22,473,000				7,180,000	22,473,000
Listed equity securities	1,203,672,000				844,001,000				1,203,672,000	844,001,000
Non-controlling interest in related party joint venture				$ 11,561,000					11,561,000
Net Income (Loss) Attributable to Noncontrolling Interest									578,000	1,819,000	(5,508,000)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders									$ (2,079,000)	7,756,000	0
Board of Directors Chairman [Member] | Investment Advisory Agreement [Member]
Related Party Transaction [Line Items]
Performance compensation full rate									20.00%
Performance compensation reduced rate									10.00%
Loss carry forward recoupment required									150.00%
Performance compensation									$ 2,079,000	8,244,000	0
Investment management fee rate - monthly									0.125%
Investment management fee rate - annual									1.50%
Management fees									$ 17,785,000	16,299,000	19,246,000
Board of Directors Chairman [Member] | Equities – listed
Related Party Transaction [Line Items]
Listed equity securities	$ 39,200,000				$ 34,800,000				39,200,000	34,800,000
Board of Directors Chairman [Member] | Service Agreement
Related Party Transaction [Line Items]
Investor relations fee monthly									5,000
Non-controlling interest in joint venture
Related Party Transaction [Line Items]
Temporary Equity, Net Income									201,000	1,375,000	(2,392,000)
Temporary Equity, Carrying Amount, Period Increase (Decrease)									(1,084,000)	7,756,000	0
Nonredeemable Noncontrolling Interest [Member]
Related Party Transaction [Line Items]
Change in non-controlling interest in related party joint venture									378,000	443,000	(3,115,000)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders									$ (994,000)	$ 0	$ 0