Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		3 Months Ended			9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		$ 18,576,000	$ 13,242,000		$ 15,811,000		$ 12,872,000
Asset, Transfers In		0	0		0		0
Asset, Transfers Out		0	0		(3,472,000)	[1]	(1,000,000)	[2]
Purchases/(covers)		0	250,000		9,000,000		450,000
(Sales)/short buys		0	0		(31,000)		(218,000)
Realized and unrealized gains (losses), asset		(587,000)	(528,000)		(3,319,000)		860,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(587,000)	(508,000)		(1,006,000)		452,000
Balance Asset Value		17,989,000	12,964,000		17,989,000		12,964,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		10,588,000	5,927,000		10,121,000		2,278,000
Asset, Transfers In		0	0		0		0
Asset, Transfers Out		0	0		0		0
Purchases/(covers)		3,151,000	3,716,000		3,182,000		5,210,000
(Sales)/short buys		(1,946,000)	0		(2,121,000)		(135,000)
Realized and unrealized gains (losses), asset		297,000	719,000		908,000		3,009,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	297,000	458,000		908,000		2,750,000
Balance Asset Value		12,090,000	10,362,000		12,090,000		10,362,000
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		282,000	250,000		250,000		819,000
Asset, Transfers In		0	0		0		0
Asset, Transfers Out		0	0		0		0
Purchases/(covers)		250,000	0		282,000		0
(Sales)/short buys		0	0		0		(569,000)
Realized and unrealized gains (losses), asset		(250,000)	0		(250,000)		0
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0	0		0		0
Balance Asset Value		282,000	250,000		282,000		250,000
Corporate Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value			319,000				0
Asset, Transfers In			0				0
Asset, Transfers Out			0				0
Purchases/(covers)			0				279,000
(Sales)/short buys			(179,000)				(179,000)
Realized and unrealized gains (losses), asset			80,000				120,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]		45,000				85,000
Balance Asset Value			220,000				220,000
Options
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		9,860,000	8,547,000		14,753,000		18,194,000
Asset, Transfers In		0	0		0		0
Asset, Transfers Out		0	0		0		0
Purchases/(covers)		0	0		0		0
(Sales)/short buys		0	0		0		0
Realized and unrealized gains (losses), asset		499,000	4,414,000		(4,394,000)		(5,233,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	499,000	4,414,000		(4,394,000)		(5,233,000)
Balance Asset Value		10,359,000	12,961,000		10,359,000		12,961,000
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		3,409,000	3,303,000		3,719,000		2,572,000
Asset, Transfers In		0	0		3,192,000	[4],[5]	0
Asset, Transfers Out		0	0		0		0
Purchases/(covers)		0	0		0		1,914,000
(Sales)/short buys		0	0		(4,367,000)		(817,000)
Realized and unrealized gains (losses), asset		(1,013,000)	254,000		(148,000)		(112,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	187,000	252,000		510,000		(87,000)
Balance Asset Value		2,396,000	3,557,000		2,396,000		3,557,000
Trade Claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		4,648,000			562,000
Asset, Transfers In		0			0
Asset, Transfers Out		0			0
Purchases/(covers)		1,925,000			5,865,000
(Sales)/short buys		(630,000)			(700,000)
Realized and unrealized gains (losses), asset		3,000			219,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	3,000			198,000
Balance Asset Value		5,946,000			5,946,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		309,000	270,000		265,000		299,000
Asset, Transfers In		0	0		0		0
Asset, Transfers Out		0	0		0		0
Purchases/(covers)		0	0		0		0
(Sales)/short buys		0	0		0		0
Realized and unrealized gains (losses), asset		10,000	13,000		54,000		(16,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	10,000	13,000		54,000		(16,000)
Balance Asset Value		319,000	283,000		319,000		283,000
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		18,224,000	41,000,000		36,928,000		32,000,000
Asset, Transfers In		0	0		0		0
Asset, Transfers Out		0	7,000,000	[1]	(13,668,000)	[1]	(11,000,000)	[1]
Purchases/(covers)		467,000	467,000		467,000		13,467,000
(Sales)/short buys		0	0		(11,853,000)		0
Realized and unrealized gains (losses), asset		252,000	2,424,000		7,069,000		2,424,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	252,000	2,424,000		2,958,000		2,424,000
Balance Asset Value		18,943,000	36,891,000		18,943,000		36,891,000
Consolidated Funds | Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		848,000			295,000
Asset, Transfers In		0			0
Asset, Transfers Out		0			0
Purchases/(covers)		0			476,000
(Sales)/short buys		(848,000)			(848,000)
Realized and unrealized gains (losses), asset		0			77,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0			0
Balance Asset Value		0			0
Consolidated Funds | Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		3,369,000			3,000		0
Asset, Transfers In		0	0		0		0
Asset, Transfers Out		0	0		0		0
Purchases/(covers)		0	0		0		0
(Sales)/short buys		0	0		0		0
Realized and unrealized gains (losses), asset		9,000	3,000		3,375,000		3,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	9,000	3,000		3,375,000		3,000
Balance Asset Value		3,378,000	3,000		3,378,000		3,000
Consolidated Funds | Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		202,000			657,000
Asset, Transfers In		0			0
Asset, Transfers Out		0			0
Purchases/(covers)		0			202,000
(Sales)/short buys		(200,000)			(1,021,000)
Realized and unrealized gains (losses), asset		(2,000)			162,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0			0
Balance Asset Value		0			0
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		9,860,000	8,547,000		14,753,000		18,194,000
Liability, Transfers In		0	0		0		0
Liability, Transfers Out		0	0		0		0
Liability, Purchases		0	0		0		0
Liability, Sales		0	0		0		0
Realized and unrealized gains (losses), liability		499,000	4,414,000		(4,394,000)		(5,233,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	499,000	4,414,000		(4,394,000)		(5,233,000)
Balance Liability Value		10,359,000	12,961,000		10,359,000		12,961,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		5,174,000	7,197,000		5,997,000		6,158,000
Liability, Transfers In		0	0		0		0
Liability, Transfers Out		0	0		0		0
Liability, Purchases		0	0		0		2,397,000
Liability, Sales		(125,000)	0		(392,000)		(3,493,000)
Realized and unrealized gains (losses), liability		0	4,000		(556,000)		2,139,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	0	4,000		(556,000)		2,139,000
Balance Liability Value		$ 5,049,000	$ 7,201,000		$ 5,049,000		$ 7,201,000

[1] The investments were converted to common stock.

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

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

[4] As part of the preferred stock sale, the sellers received contingent value rights to be paid in the event certain milestones are reached.

[5] The Company received warrants as part of a transaction.