Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		3 Months Ended				6 Months Ended
		Jun. 30, 2019		Jun. 30, 2018		Jun. 30, 2019		Jun. 30, 2018
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		$ 7,157,000		$ 8,817,000		$ 5,168,000		$ 8,115,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		1,243,000		0		3,243,000		1,415,000
(Sales)/short buys		(1,000,000)		(217,000)		(1,000,000)		(695,000)
Realized and unrealized gains (losses), asset		1,000		(1,178,000)		(10,000)		(1,413,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	1,000		(1,817,000)		(10,000)		(1,331,000)
Balance Asset Value		7,401,000		7,422,000		7,401,000		7,422,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		4,951,000		7,400,000		9,850,000		7,570,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		12,896,000		221,000		14,158,000		531,000
(Sales)/short buys		(6,519,000)		(1,200,000)		(12,472,000)		(1,333,000)
Realized and unrealized gains (losses), asset		(322,000)		(572,000)		(530,000)		(919,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	(325,000)		(547,000)		(332,000)		(959,000)
Balance Asset Value		11,006,000		5,849,000		11,006,000		5,849,000
Corporate Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		261,000				0
Asset, Transfers In		0				0
Asset, Transfers Out		0				0
Purchases/(covers)		514,000				775,000
(Sales)/short buys		0				0
Realized and unrealized gains (losses), asset		0				0
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	0				0
Balance Asset Value		775,000				775,000
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		5,000,000				3,000,000		282,000
Asset, Transfers In						0		0
Asset, Transfers Out		(2,025,000)	[2]			(2,025,000)	[2]	0
Purchases/(covers)		9,971,000				14,971,000		0
(Sales)/short buys		(6,692,000)				(9,692,000)		(307,000)
Realized and unrealized gains (losses), asset		64,000				64,000		25,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	64,000				64,000		0
Balance Asset Value		6,318,000		0		6,318,000		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	[1]							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		454,000		1,702,000		1,666,000		2,517,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		(374,000)	[2]	0		(374,000)	[2]
Purchases/(covers)		0		0		0		0
(Sales)/short buys		0		(143,000)		(116,000)		(143,000)
Realized and unrealized gains (losses), asset		141,000		71,000		(955,000)		(744,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	141,000		(1,176,000)		32,000		(666,000)
Balance Asset Value		595,000		1,256,000		595,000		1,256,000
Trade Claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		5,487,000		5,955,000		5,543,000		5,950,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		5,095,000		0		5,095,000		0
(Sales)/short buys		(96,000)		(334,000)		(152,000)		(334,000)
Realized and unrealized gains (losses), asset		2,000		78,000		2,000		83,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	0		14,000		0		20,000
Balance Asset Value		10,488,000		5,699,000		10,488,000		5,699,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value				312,000				301,000
Asset, Transfers In				0				0
Asset, Transfers Out				0				0
Purchases/(covers)				0				0
(Sales)/short buys				0				0
Realized and unrealized gains (losses), asset				(17,000)				(6,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[1]			(18,000)				(6,000)
Balance Asset Value				295,000				295,000
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		24,322,000		11,893,000		24,314,000		50,445,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		(38,552,000)	[3]
Purchases/(covers)		0		3,066,000		0		3,066,000
(Sales)/short buys		0		0		0		0
Realized and unrealized gains (losses), asset		0		9,355,000		8,000		9,355,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	0		9,356,000		8,000		9,356,000
Balance Asset Value		24,322,000		24,314,000		24,322,000		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		50,000		94,000		50,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		0		0		407,000		0
(Sales)/short buys		0		0		0		0
Realized and unrealized gains (losses), asset		0		44,000		516,000		44,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	0		43,000		516,000		43,000
Balance Asset Value		1,017,000		94,000		1,017,000		94,000
Consolidated Funds | Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		4,708,000		5,254,000		5,279,000		3,568,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		(20,000)	[3]
Purchases/(covers)		0		(1,340,000)		0		(1,340,000)
(Sales)/short buys		0		0		(1,088,000)		0
Realized and unrealized gains (losses), asset		1,566,000		824,000		2,083,000		2,530,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	1,566,000		(516,000)		995,000		1,190,000
Balance Asset Value		6,274,000		4,738,000		6,274,000		4,738,000
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		1,733,000		21,395,000		2,096,000		22,401,000
Liability, Transfers In		0		0		0		0
Liability, Transfers Out		0		(28,973,000)	[4]	0		(28,973,000)	[4]
Liability, Purchases		0		0		0		0
Liability, Sales		0		(259,000)		(4,000)		(259,000)
Realized and unrealized gains (losses), liability		1,046,000		8,138,000		687,000		7,132,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	[1]	1,046,000		8,138,000		687,000		7,132,000
Balance Liability Value		2,779,000		301,000		2,779,000		301,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		29,536,000		3,440,000		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		(570,000)		(1,234,000)		(570,000)
Realized and unrealized gains (losses), liability		0		0		0		0
Change in Unrealized Gain (Loss), instruments still held, liabilities	[1]	0		0		0		0
Balance Liability Value		$ 29,536,000		$ 2,870,000		$ 29,536,000		$ 2,870,000

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

[2] The investments were converted to common stock.

[3] The Company deconsolidated an investment fund.

[4] 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).