Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		3 Months Ended				6 Months Ended
		Jun. 30, 2016		Jun. 30, 2015		Jun. 30, 2016		Jun. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value						$ 70,034,000
Balance Liability Value						24,352,000
Balance Asset Value		$ 74,357,000				74,357,000
Balance Liability Value		15,744,000				15,744,000
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		13,646,000		$ 19,480,000		12,872,000		$ 12,517,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		(1,000,000)	[1]	(6,823,000)	[2]	(1,000,000)	[1]	(6,823,000)	[1]
Purchases/(covers)		200,000		10,875,000		200,000		18,250,000
(Sales)/short buys		0		0		(218,000)		0
Realized and unrealized gains (losses), asset		396,000		(70,000)		1,388,000		(482,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	394,000		(70,000)		960,000		(483,000)
Balance Asset Value		13,242,000		23,462,000		13,242,000		23,462,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		6,265,000		411,000		3,278,000		412,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		1,204,000		0		2,273,000		0
(Sales)/short buys		(135,000)		(28,000)		(135,000)		(31,000)
Realized and unrealized gains (losses), asset		411,000		21,000		2,329,000		23,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	276,000		7,000		2,330,000		12,000
Balance Asset Value		7,745,000		404,000		7,745,000		404,000
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		0		0		0
(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		879,000		250,000		879,000
Options
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		20,892,000		41,642,000		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		(12,345,000)		16,934,000		(9,647,000)		21,769,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(12,345,000)		16,934,000		(9,647,000)		21,769,000
Balance Asset Value		8,547,000		58,576,000		8,547,000		58,576,000
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		2,505,000		2,559,000		2,572,000		1,322,000
Asset, Transfers In		0		0		0		0
Asset, Transfers Out		0		0		0		0
Purchases/(covers)		1,914,000		0		1,914,000		26,000
(Sales)/short buys		(817,000)		(57,000)		(817,000)		(71,000)
Realized and unrealized gains (losses), asset		(299,000)		(186,000)		(366,000)		1,039,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	402,000		(212,000)		(353,000)		985,000
Balance Asset Value		3,303,000		2,316,000		3,303,000		2,316,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		293,000		361,000		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		(23,000)		(14,000)		(29,000)		(33,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(23,000)		(14,000)		(29,000)		(33,000)
Balance Asset Value		270,000		347,000		270,000		347,000
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		28,000,000				32,000,000
Asset, Transfers In		0
Asset, Transfers Out		0				(4,000,000)	[2]
Purchases/(covers)		13,000,000				13,000,000
(Sales)/short buys		0				0
Realized and unrealized gains (losses), asset		0				0
Change in Unrealized Gain (Loss), instruments still held, asset		0				0	[3]
Balance Asset Value		41,000,000				41,000,000
Consolidated Funds | Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value				494,000				493,000
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				250,000				251,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]			250,000				250,000
Balance Asset Value				744,000				744,000
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		20,892,000		41,642,000		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		(12,345,000)		16,934,000		(9,647,000)		21,769,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	(12,345,000)		16,934,000		(9,647,000)		21,769,000
Balance Liability Value		8,547,000		58,576,000		8,547,000		58,576,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		8,293,000		3,974,000		6,158,000		4,083,000
Liability, Transfers In		0		0		0		0
Liability, Transfers Out		0		0		0		0
Liability, Purchases		2,397,000		0		2,397,000		0
Liability, Sales		(3,493,000)		(1,616,000)		(3,493,000)		(1,725,000)
Realized and unrealized gains (losses), liability		0		0		2,135,000		0
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	0		0		2,135,000		0
Balance Liability Value		$ 7,197,000		$ 2,358,000		$ 7,197,000		$ 2,358,000

[1] The investment completed an initial public offering.

[2] The investment was converted to equity.

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