Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		$ 8,115,000		$ 15,811,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		1,415,000		1,732,000
(Sales)/short buys		(478,000)		(31,000)
Realized and unrealized gains (losses), asset		(235,000)		(996,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	486,000		(996,000)
Balance Asset Value		8,817,000		16,516,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		7,570,000		10,121,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		310,000		31,000
(Sales)/short buys		(133,000)		(52,000)
Realized and unrealized gains (losses), asset		(347,000)		404,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	412,000		404,000
Balance Asset Value		7,400,000		10,504,000
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		282,000		250,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		(307,000)		0
Realized and unrealized gains (losses), asset		25,000		0
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	0		0
Balance Asset Value		0		250,000
Options
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		1,455,000		14,753,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		(1,455,000)		0
Realized and unrealized gains (losses), asset		0		(7,782,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	0		(7,782,000)
Balance Asset Value		0		6,971,000
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		2,517,000		3,719,000
Asset, Transfers In		0		451,000	[2]
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		0		0
Realized and unrealized gains (losses), asset		(815,000)		(31,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	510,000		(31,000)
Balance Asset Value		1,702,000		4,139,000
Trade Claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		5,950,000		562,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		0		(70,000)
Realized and unrealized gains (losses), asset		5,000		211,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	5,000		190,000
Balance Asset Value		5,955,000		703,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		301,000		265,000
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		11,000		32,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	12,000		32,000
Balance Asset Value		312,000		297,000
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		50,445,000		36,928,000
Asset, Transfers In		0		0
Asset, Transfers Out		(38,552,000)	[3]	0
Purchases/(covers)		0		0
(Sales)/short buys		0		0
Realized and unrealized gains (losses), asset		0		3,387,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	0		3,887,000
Balance Asset Value		11,893,000		40,315,000
Consolidated Funds | Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		50,000		295,000
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		0		1,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	0		1,000
Balance Asset Value		50,000		296,000
Consolidated Funds | Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		3,568,000		3,000
Asset, Transfers In		0		0
Asset, Transfers Out		(20,000)	[3]	0
Purchases/(covers)		0		0
(Sales)/short buys		0		0
Realized and unrealized gains (losses), asset		1,706,000		(1,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[1]	1,706,000		(1,000)
Balance Asset Value		5,254,000		2,000
Consolidated Funds | Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value				657,000
Asset, Transfers In				0
Asset, Transfers Out				0
Purchases/(covers)				0
(Sales)/short buys				0
Realized and unrealized gains (losses), asset				54,000
Change in Unrealized Gain (Loss), instruments still held, asset	[1]			0
Balance Asset Value				711,000
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		22,401,000		14,753,000
Liability, Transfers In		0		0
Liability, Transfers Out		0		0
Liability, Purchases		0		0
Liability, Sales		0		0
Realized and unrealized gains (losses), liability		(1,006,000)		(7,782,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	[1]	1,006,000		(7,782,000)
Balance Liability Value		21,395,000		6,971,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		3,440,000		5,997,000
Liability, Transfers In		0		0
Liability, Transfers Out		0		0
Liability, Purchases		0		0
Liability, Sales		0		(167,000)
Realized and unrealized gains (losses), liability		0		(556,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	[1]	0		(556,000)
Balance Liability Value		$ 3,440,000		$ 5,274,000

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

[2] The Company received warrants as consideration as part of an investment banking transaction.

[3] The Company deconsolidated a fund (See note 3)