Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		$ 5,168,000		$ 8,115,000
Asset, Transfers In		0		0
Asset, Transfers Out		(1,000,000)	[1]	(1,141,000)	[2]
Purchases/(covers)		3,513,000		1,415,000
(Sales)/short buys		(1,270,000)		(695,000)
Realized and unrealized gains (losses), asset		1,424,000		(2,526,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	2,285,000		860,000
Balance Asset Value		7,835,000		5,168,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		9,850,000		7,570,000
Asset, Transfers In		10,242,000	[4],[5]	0
Asset, Transfers Out		(3,000)	[6]	(569,000)
Purchases/(covers)		11,477,000		3,324,000
(Sales)/short buys		(11,002,000)		(1,416,000)
Realized and unrealized gains (losses), asset		(3,098,000)		941,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(3,098,000)		1,797,000
Balance Asset Value		17,466,000		9,850,000
Corporate Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		0
Balance Liability Value		0
Asset, Transfers In	[5]	4,000
Liability, Transfers In	[5]	2,525,000
Liability, Transfers Out		0
Asset, Transfers Out		0
Purchases/(covers)		2,811,000
Liability, Purchases		0
(Sales)/short buys		(533,000)
Liability, Sales		0
Realized and unrealized gains (losses), asset		139,000
Realized and unrealized gains (losses), liability		1,525,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	140,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	1,525,000
Balance Asset Value		2,421,000		0
Balance Liability Value		1,000,000		0
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		3,000,000		282,000
Asset, Transfers In		0		0
Asset, Transfers Out		(4,826,000)	[1],[2]	0
Purchases/(covers)		11,354,000		3,000,000
(Sales)/short buys		(7,072,000)		(307,000)
Realized and unrealized gains (losses), asset		44,000		25,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(25,000)		0
Balance Asset Value		2,500,000		3,000,000
Options
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		0		1,455,000
Asset, Transfers In		330,000	[4]	0
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		0		(1,455,000)
Realized and unrealized gains (losses), asset		6,000		0
Change in Unrealized Gain (Loss), instruments still held, asset		6,000		0	[3]
Balance Asset Value		336,000		0
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		1,666,000		2,517,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		(189,000)		(143,000)
Realized and unrealized gains (losses), asset		(883,000)		(708,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	31,000		(850,000)
Balance Asset Value		594,000		1,666,000
Trade Claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		5,543,000		5,950,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		7,205,000		44,000
(Sales)/short buys		(5,506,000)		(536,000)
Realized and unrealized gains (losses), asset		78,000		85,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	76,000		0
Balance Asset Value		7,320,000		5,543,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		0		301,000
Asset, Transfers In				0
Asset, Transfers Out				0
Purchases/(covers)				0
(Sales)/short buys				(234,000)
Realized and unrealized gains (losses), asset				(67,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]			0
Balance Asset Value				0
US Government Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		0
Liability, Transfers In	[5]	4,681,000
Liability, Transfers Out		0
Liability, Purchases		0
Liability, Sales		0
Realized and unrealized gains (losses), liability		(2,731,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	2,731,000
Balance Liability Value		1,950,000		0
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		24,314,000		50,445,000
Asset, Transfers In		0		0
Asset, Transfers Out		(19,929,000)	[1]	(38,552,000)	[7]
Purchases/(covers)		0		3,066,000
(Sales)/short buys		0		0
Realized and unrealized gains (losses), asset		8,000		9,355,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0		9,355,000
Balance Asset Value		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		94,000		50,000
Asset, Transfers In		0		0
Asset, Transfers Out		(94,000)	[1]	0
Purchases/(covers)		407,000		0
(Sales)/short buys		(958,000)		0
Realized and unrealized gains (losses), asset		551,000		44,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0		44,000
Balance Asset Value		0		94,000
Consolidated Funds | Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		5,279,000		3,568,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		(20,000)	[7]
Purchases/(covers)		0		0
(Sales)/short buys		(1,758,000)		(1,340,000)
Realized and unrealized gains (losses), asset		2,046,000		3,071,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	289,000		1,730,000
Balance Asset Value		5,567,000		5,279,000
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		2,096,000		22,401,000
Liability, Transfers In		0		0
Liability, Transfers Out		0		(28,973,000)	[8]
Liability, Purchases		0		0
Liability, Sales		(4,000)		(259,000)
Realized and unrealized gains (losses), liability		828,000		8,927,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	(828,000)		(8,927,000)
Balance Liability Value		2,920,000		2,096,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		3,070,000		3,440,000
Liability, Transfers In		0		0
Liability, Transfers Out		0		0
Liability, Purchases		27,700,000		427,000
Liability, Sales		(1,234,000)		(797,000)
Realized and unrealized gains (losses), liability		1,360,000		0
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	(1,360,000)		0
Balance Liability Value		$ 30,896,000		$ 3,070,000

[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 consolidated statements of operations.

[4] The holding Company which held common stock and options was liquidated

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

[6] Shares of common stock were exchanged for liquid warrants and rights of an acquired company.

[7] The Company deconsolidated an investment fund.

[8] On June 26, 2018, the Company received shareholder approval which allows the Company to settle its convertible note (see Note 23) 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 24).