Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		3 Months Ended				9 Months Ended
		Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		$ 7,401,000		$ 7,422,000		$ 5,168,000		$ 8,115,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		(1,000,000)	[1]	(1,141,000)	[2]	(1,000,000)	[1]	(1,141,000)	[2]
Purchases/(covers)		0		0		3,243,000		1,415,000
(Sales)/short buys		0		0		(1,000,000)		(695,000)
Realized and unrealized gains (losses), asset		1,434,000		(1,123,000)		1,424,000		(2,536,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	2,295,000		(1,124,000)		2,285,000		(2,301,000)
Balance Asset Value		7,835,000		5,158,000		7,835,000		5,158,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		11,006,000		5,848,000		9,850,000		7,570,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		2,579,000		0		16,737,000		531,000
(Sales)/short buys		(480,000)		0		(12,952,000)		(1,333,000)
Realized and unrealized gains (losses), asset		208,000		(174,000)		(322,000)		(1,094,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	210,000		(174,000)		(122,000)		(1,128,000)
Balance Asset Value		13,313,000		5,674,000		13,313,000		5,674,000
Corporate Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		775,000				0
Balance Liability Value		0				0
Asset, Transfers In	[4]	20,000				20,000
Liability, Transfers In	[4]	2,525,000				2,525,000
Liability, Transfers Out		0				0
Asset, Transfers Out		0				0
Purchases/(covers)		1,117,000				1,892,000
Liability, Purchases		0				0
(Sales)/short buys		0				0
Liability, Sales		0				0
Realized and unrealized gains (losses), asset		161,000				161,000
Realized and unrealized gains (losses), liability		(1,325,000)				1,325,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	161,000				161,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	(1,325,000)				1,325,000
Balance Asset Value		2,073,000				2,073,000
Balance Liability Value		1,200,000				1,200,000
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		6,318,000				3,000,000		282,000
Asset, Transfers In						0		0
Asset, Transfers Out		(2,801,000)	[1]			(4,826,000)	[1],[2]	0
Purchases/(covers)		1,049,000				16,021,000		0
(Sales)/short buys		(2,072,000)				(11,764,000)		(307,000)
Realized and unrealized gains (losses), asset		47,000				110,000		25,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	4,000				41,000		0
Balance Asset Value		2,541,000		0		2,541,000		0
Options
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value								1,455,000
Asset, Transfers In								0
Asset, Transfers Out								0
Purchases/(covers)								0
(Sales)/short buys								(1,455,000)
Realized and unrealized gains (losses), asset								0
Change in Unrealized Gain (Loss), instruments still held, asset	[3]							0
Balance Asset Value				0				0
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		595,000		1,544,000		1,666,000		2,517,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		0		0		0		0
(Sales)/short buys		(72,000)				(188,000)		(143,000)
Realized and unrealized gains (losses), asset		61,000		38,000		(894,000)		(792,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(12,000)		38,000		20,000		(933,000)
Balance Asset Value		584,000		1,582,000		584,000		1,582,000
Trade Claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		10,488,000		5,699,000		5,543,000		5,950,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		1,871,000		44,000		6,965,000		44,000
(Sales)/short buys		(5,354,000)		0		(5,506,000)		(334,000)
Realized and unrealized gains (losses), asset		57,000		3,000		60,000		86,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	57,000		3,000		57,000		23,000
Balance Asset Value		7,062,000		5,746,000		7,062,000		5,746,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value				295,000				301,000
Asset, Transfers In				0				0
Asset, Transfers Out				0				0
Purchases/(covers)				0				0
(Sales)/short buys				(234,000)				(234,000)
Realized and unrealized gains (losses), asset				(61,000)				(67,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]			0				0
Balance Asset Value				0				0
US Government Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		0				0
Liability, Transfers In	[4]	4,681,000				4,681,000
Liability, Transfers Out		0				0
Liability, Purchases		0				0
Liability, Sales		0				0
Realized and unrealized gains (losses), liability		2,431,000				(2,431,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	2,431,000				2,431,000
Balance Liability Value		2,250,000				2,250,000
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		24,322,000		24,314,000		24,314,000		50,445,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		19,929,000	[1]	0		(19,929,000)	[1]	(38,552,000)	[5]
Purchases/(covers)		0		0		0		3,066,000
(Sales)/short buys		0		0		0		0
Realized and unrealized gains (losses), asset		0		0		8,000		9,355,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0		0		8,000		9,355,000
Balance Asset Value		4,393,000		24,314,000		4,393,000		24,314,000
Consolidated Funds | Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		1,017,000		94,000		94,000		50,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		94,000	[1]	0		(94,000)	[1]	0
Purchases/(covers)		0		0		407,000		0
(Sales)/short buys		(957,000)		0		(958,000)		0
Realized and unrealized gains (losses), asset		34,000		0		551,000		44,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0		0		0		44,000
Balance Asset Value		0		94,000		0		94,000
Consolidated Funds | Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		6,274,000		4,738,000		5,279,000		3,568,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		(20,000)	[5]
Purchases/(covers)		0				0		(1,340,000)
(Sales)/short buys		(670,000)		0		(1,758,000)		0
Realized and unrealized gains (losses), asset		(139,000)		110,000		1,944,000		2,640,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(809,000)		110,000		190,000		1,300,000
Balance Asset Value		5,465,000		4,848,000		5,465,000		4,848,000
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		2,779,000		301,000		2,096,000		22,401,000
Liability, Transfers In		0		0		0		0
Liability, Transfers Out		0		0		0		(28,973,000)	[6]
Liability, Purchases		0		0		0		0
Liability, Sales		0		0		(4,000)		(259,000)
Realized and unrealized gains (losses), liability		(279,000)		2,246,000		408,000		9,378,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	279,000		(2,246,000)		(408,000)		(9,378,000)
Balance Liability Value		2,500,000		2,547,000		2,500,000		2,547,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		29,536,000		2,870,000		3,070,000		3,440,000
Liability, Transfers In		0		0		0		0
Liability, Transfers Out		0		0		0		0
Liability, Purchases		0		0		27,700,000		0
Liability, Sales		0		(227,000)		(1,234,000)		(797,000)
Realized and unrealized gains (losses), liability		298,000		0		298,000		0
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	(298,000)		0		(298,000)		0
Balance Liability Value		$ 29,834,000		$ 2,643,000		$ 29,834,000		$ 2,643,000

[1] The entity in which the Company is invested completed an initial public offering

[2] The investments were converted to common stock.

[3] Unrealized gains/losses are reported in other income (loss) in the accompanying condensed consolidated statements of operations.

[4] The investments had a change of valuation methodology due to increased activity in foreign market.

[5] The Company deconsolidated an investment fund.

[6] On June 26, 2018, the Company received shareholder approval which allows the Company to settle its convertible note (see Note 18) entirely in class A common shares. Upon receiving shareholder approval, the Company reclassified the embedded conversion option, associated with the convertible debt, to equity. (see Note 19).