Long-Term 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	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity-method investments	$ 10,639		$ 10,639		$ 11,631
Proceeds from long-term equity method investment			855	$ 779
In-transit redemptions recorded from proceeds from investments redeemed that qualify for NAV practical expedient			4,271
Equity in (losses) earnings from investments	(1,685)	$ 4,813	(323)	$ 5,975
Indian Creek Investors LP (“Indian Creek”)
Schedule of Equity Method Investments [Line Items]
Equity-method investments	$ 719		$ 719		1,167
Equity-method ownership percentage	12.52%		12.52%
Boyar Value Fund (“Boyar”)
Schedule of Equity Method Investments [Line Items]
Equity-method investments	$ 9,444		$ 9,444		8,384
Equity-method ownership percentage	34.57%		34.57%
Quoted market value	$ 9,444		$ 9,444
Ladenburg Thalmann Financial Services Inc. (“LTS”)
Schedule of Equity Method Investments [Line Items]
Equity-method investments	$ 476		$ 476		2,080
Equity-method ownership percentage	10.29%		10.29%
Quoted market value	$ 52,106		$ 52,106
Castle Brands, Inc. (“Castle”)
Schedule of Equity Method Investments [Line Items]
Equity-method investments	$ 0		$ 0		$ 0
Equity-method ownership percentage	7.63%		7.63%
Quoted market value	$ 5,932		$ 5,932