Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		3 Months Ended				9 Months Ended
		Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, Between Level 1 and 2 transfers, amount		$ 0				$ 0
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		13,242,000		$ 23,462,000		12,872,000		$ 12,517,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		9,000,000	[1],[2]	1,000,000	[2]	15,823,000	[1],[2]
Purchases/(covers)		250,000		3,500,000		450,000		21,750,000
(Sales)/short buys		0		(6,665,000)		(218,000)		(6,665,000)
Realized and unrealized gains (losses), asset		(528,000)		4,474,000		860,000		3,992,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(508,000)		1,200,000		452,000		717,000
Balance Asset Value		12,964,000		15,771,000		12,964,000		15,771,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		7,427,000		404,000		3,278,000		412,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		3,716,000		104,000		5,710,000		104,000
(Sales)/short buys		0		(89,000)		(135,000)		(120,000)
Realized and unrealized gains (losses), asset		458,000		(102,000)		2,748,000		(79,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	458,000		(87,000)		2,750,000		(74,000)
Balance Asset Value		11,601,000		317,000		11,601,000		317,000
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		250,000		879,000		819,000		900,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		0		250,000		0		250,000
(Sales)/short buys		0		0		(569,000)		0
Realized and unrealized gains (losses), asset		0		0		0		(21,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0		0		0		(21,000)
Balance Asset Value		250,000		1,129,000		250,000		1,129,000
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		8,547,000		58,576,000		18,194,000		36,807,000
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		4,414,000		(36,985,000)		(5,233,000)		(15,216,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	4,414,000		(36,985,000)		(5,233,000)		(15,216,000)
Balance Asset Value		12,961,000		21,591,000		12,961,000		21,591,000
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		3,303,000		2,316,000		2,572,000		1,322,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		0		0		1,914,000		26,000
(Sales)/short buys		0		0		(817,000)		(71,000)
Realized and unrealized gains (losses), asset		254,000		678,000		(112,000)		1,717,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	252,000		878,000		(87,000)		1,757,000
Balance Asset Value		3,557,000		2,994,000		3,557,000		2,994,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		270,000		347,000		299,000		380,000
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		13,000		(12,000)		(16,000)		(45,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	13,000		(12,000)		(16,000)		(45,000)
Balance Asset Value		283,000		335,000		283,000		335,000
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		41,000,000		0		32,000,000		0
Asset, Transfers In		0		0
Asset, Transfers Out		(7,000,000)	[2]	7,000,000	[1]	11,000,000	[2]	(7,000,000)	[1]
Purchases/(covers)		467,000		12,000,000		13,467,000		12,000,000
(Sales)/short buys		0		0		0		0
Realized and unrealized gains (losses), asset		2,424,000		0		2,424,000		0
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	2,424,000		0		2,424,000		0
Balance Asset Value		36,891,000		19,000,000		36,891,000		19,000,000
Consolidated Funds | Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		0				0
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		3,000				3,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	3,000				3,000
Balance Asset Value		3,000				3,000
Consolidated Funds | Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value				744,000				493,000
Asset, Transfers In				0				0
Asset, Transfers Out				0				0
Purchases/(covers)				0				0
(Sales)/short buys				(739,000)				(739,000)
Realized and unrealized gains (losses), asset				(5,000)				246,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]			0				250,000
Balance Asset Value				0				0
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		8,547,000		58,576,000		18,194,000		36,807,000
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		4,414,000		(36,985,000)		(5,233,000)		(15,216,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	4,414,000		(36,985,000)		(5,233,000)		(15,216,000)
Balance Liability Value		12,961,000		21,591,000		12,961,000		21,591,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		7,197,000		2,358,000		6,158,000		4,083,000
Liability, Transfers In		0		0		0		0
Liability, Transfers Out		0		0		0		0
Liability, Purchases		0		3,100,000		2,397,000		3,100,000
Liability, Sales		0		0		(3,493,000)		(1,725,000)
Realized and unrealized gains (losses), liability		4,000		0		2,139,000		0
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	4,000		0		2,139,000		0
Balance Liability Value		$ 7,201,000		$ 5,458,000		$ 7,201,000		$ 5,458,000

[1] The company transferred investments to a consolidated fund.

[2] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmY3YjUwOGYzOTIwYTQ2ODY5Y2M0Y2QzOTMwZmYzZGM0fFRleHRTZWxlY3Rpb246NUEwQTk2NkMyRUREM0FEQUYzNTA0NjhEODcxREVGRjQM}

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