Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		3 Months Ended			9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value					$ 55,006,000
Balance Liability Value					40,890,000
Balance Asset Value		$ 63,053,000			63,053,000
Balance Liability Value		27,049,000			27,049,000
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		23,462,000		$ 2,574,000	12,517,000		$ 324,000
Asset, Transfers In		0		0	0		0
Asset, Transfers Out	[1]	(9,000,000)	[2]	(2,000,000)	(15,823,000)	[2]	(2,000,000)
Purchases/(covers)		3,500,000		0	21,750,000		2,250,000
(Sales)/short buys		(6,665,000)		0	(6,665,000)		0
Realized and unrealized gains (losses), asset		4,474,000		0	3,992,000		0
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	1,200,000		0	717,000		0
Balance Asset Value		15,771,000		574,000	15,771,000		574,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		404,000		419,000	412,000		3,559,000
Asset, Transfers In		0		0	0		0
Asset, Transfers Out		0		0	0		(3,150,000)	[1]
Purchases/(covers)		104,000		0	104,000		9,000
(Sales)/short buys		(89,000)		(1,000)	(120,000)		(1,000)
Realized and unrealized gains (losses), asset		(102,000)		(128,000)	(79,000)		(127,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(87,000)		(14,000)	(74,000)		(13,000)
Balance Asset Value		317,000		290,000	317,000		290,000
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		879,000		1,750,000	900,000		1,950,000
Asset, Transfers In		0		0	0		0
Asset, Transfers Out		0		0	0		0
Purchases/(covers)		250,000		0	250,000		0
(Sales)/short buys		0		0	0		(200,000)
Realized and unrealized gains (losses), asset		0		0	(21,000)		0
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0		0	(21,000)		0
Balance Asset Value		1,129,000		1,750,000	1,129,000		1,750,000
Options
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		58,576,000		37,658,000	36,807,000		0
Asset, Transfers In		0		0	0		0
Asset, Transfers Out		0		0	0		0
Purchases/(covers)		0		0	0		35,710,000
(Sales)/short buys		0		0	0		0
Realized and unrealized gains (losses), asset		(36,985,000)		(8,873,000)	(15,216,000)		(6,925,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(36,985,000)		(8,873,000)	(15,216,000)		(6,925,000)
Balance Asset Value		21,591,000		28,785,000	21,591,000		28,785,000
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		2,316,000		3,346,000	1,322,000		5,805,000
Asset, Transfers In		0		0	0		0
Asset, Transfers Out		0		0	0		0
Purchases/(covers)		0		57,000	26,000		57,000
(Sales)/short buys		0		(57,000)	(71,000)		(1,385,000)
Realized and unrealized gains (losses), asset		678,000		(738,000)	1,717,000		(1,869,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	878,000		(434,000)	1,757,000		(432,000)
Balance Asset Value		2,994,000		2,608,000	2,994,000		2,608,000
Real Estate Investments, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		1,987,000		2,262,000	2,175,000		2,088,000
Asset, Transfers In		0		0	0		0
Asset, Transfers Out		0		0	0		0
Purchases/(covers)		0		0	0		50,000,000
(Sales)/short buys		(70,000)		0	(377,000)		(50,027,000)
Realized and unrealized gains (losses), asset		(1,000)		23,000	118,000		224,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(1,000)		23,000	118,000		224,000
Balance Asset Value		1,916,000		2,285,000	1,916,000		2,285,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		347,000		418,000	380,000		378,000
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		(76,000)
Realized and unrealized gains (losses), asset		(12,000)		(58,000)	(45,000)		58,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	(12,000)		(58,000)	(45,000)		58,000
Balance Asset Value		335,000		360,000	335,000		360,000
Consolidated Funds | Preferred Stock
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	[2]	(7,000,000)			7,000,000
Purchases/(covers)		12,000,000			12,000,000
(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		19,000,000			19,000,000
Consolidated Funds | Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		744,000		4,090,000	493,000		4,842,000
Asset, Transfers In		0		0	0		0
Asset, Transfers Out		0		0	0		0
Purchases/(covers)		0		0	0		0
(Sales)/short buys		(739,000)		(3,731,000)	(739,000)		(4,711,000)
Realized and unrealized gains (losses), asset		(5,000)		2,000	246,000		230,000
Change in Unrealized Gain (Loss), instruments still held, asset	[3]	0		2,000	0		230,000
Balance Asset Value		0		361,000	0		361,000
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		58,576,000		37,658,000	36,807,000		0
Liability, Transfers In		0		0	0		0
Liability, Transfers Out		0		0	0		0
Liability, Purchases		0		0	0		(35,710,000)
Liability, Sales		0		0	0		0
Realized and unrealized gains (losses), liability		(36,985,000)		(8,873,000)	(15,216,000)		(6,925,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	(36,985,000)		(8,873,000)	(15,216,000)		(6,925,000)
Balance Liability Value		21,591,000		28,785,000	21,591,000		28,785,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		2,358,000		6,783,000	4,083,000		6,937,000
Liability, Transfers In		0		0	0		0
Liability, Transfers Out		0		0	0		0
Liability, Purchases		(3,100,000)		0	(3,100,000)		0
Liability, Sales		0		(364,000)	(1,725,000)		(518,000)
Realized and unrealized gains (losses), liability		0		0	0		0
Change in Unrealized Gain (Loss), instruments still held, liabilities	[3]	0		0	0		0
Balance Liability Value		$ 5,458,000		$ 6,419,000	$ 5,458,000		$ 6,419,000

[1] The company completed an initial public offering.

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

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