Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	$ 259,530,000		$ 226,269,000
Balance Liability Value	40,890,000		6,937,000
Fair value, Between Level 1 and 2 transfers, amount	0
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	324,000		2,332,000
Asset, Transfers In	0		0
Asset, Transfers Out	(2,000,000)	[1]	(2,000,000)	[1]
Purchases/(covers)	14,396,000		0
(Sales)/short buys	0		0
Realized and unrealized gains (losses), asset	(203,000)		(8,000)
Change in Unrealized Gain (Loss), instruments still held, asset	(203,000)	[2]	(8,000)	[2]
Balance Asset Value	12,517,000		324,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	3,559,000		2,549,000
Asset, Transfers In	0		0
Asset, Transfers Out	(3,150,000)	[1]	0
Purchases/(covers)	12,000		4,000
(Sales)/short buys	(1,000)		(275,000)
Realized and unrealized gains (losses), asset	(8,000)		1,281,000
Change in Unrealized Gain (Loss), instruments still held, asset	(135,000)	[2]	1,451,000	[2]
Balance Asset Value	412,000		3,559,000
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	1,950,000		0
Asset, Transfers In	0		0
Asset, Transfers Out	0		0
Purchases/(covers)	0		3,938,000
(Sales)/short buys	(200,000)		(1,988,000)
Realized and unrealized gains (losses), asset	(850,000)		0
Change in Unrealized Gain (Loss), instruments still held, asset	(850,000)	[2]	0	[2]
Balance Asset Value	900,000		1,950,000
Corporate Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value			515,000
Asset, Transfers In			0
Asset, Transfers Out			0
Purchases/(covers)			2,735,000
(Sales)/short buys			(3,346,000)
Realized and unrealized gains (losses), asset			96,000
Change in Unrealized Gain (Loss), instruments still held, asset			0	[2]
Balance Asset Value			0
Options, asset
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	0
Asset, Transfers In	0
Asset, Transfers Out	0
Purchases/(covers)	35,710,000
(Sales)/short buys	0
Realized and unrealized gains (losses), asset	1,097,000
Change in Unrealized Gain (Loss), instruments still held, asset	1,097,000	[2]
Balance Asset Value	36,807,000
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	5,805,000		1,713,000
Asset, Transfers In	0		291,000	[3]
Asset, Transfers Out	(1,288,000)		0
Purchases/(covers)	57,000		166,000
(Sales)/short buys	(97,000)		(110,000)
Realized and unrealized gains (losses), asset	(3,155,000)		3,745,000
Change in Unrealized Gain (Loss), instruments still held, asset	(1,415,000)	[2]	4,011,000	[2]
Balance Asset Value	1,322,000		5,805,000
Portfolio Funds, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	51,649,000		25,670,000
Asset, Transfers In	0		13,128,000	[4]
Asset, Transfers Out	0		0
Purchases/(covers)	13,453,000		16,914,000
(Sales)/short buys	(9,940,000)		(9,001,000)
Realized and unrealized gains (losses), asset	11,109,000		4,938,000
Change in Unrealized Gain (Loss), instruments still held, asset	9,704,000	[2]	3,568,000	[2]
Balance Asset Value	66,271,000		51,649,000
Real Estate Investments, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	2,088,000		1,864,000
Asset, Transfers In	0		0
Asset, Transfers Out	0		0
Purchases/(covers)	50,000,000		0
(Sales)/short buys	(50,168,000)		(124,000)
Realized and unrealized gains (losses), asset	255,000		348,000
Change in Unrealized Gain (Loss), instruments still held, asset	255,000	[2]	348,000	[2]
Balance Asset Value	2,175,000		2,088,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	378,000		706,000
Asset, Transfers In	0		0
Asset, Transfers Out	0		0
Purchases/(covers)	0		0
(Sales)/short buys	(76,000)		(607,000)
Realized and unrealized gains (losses), asset	78,000		279,000
Change in Unrealized Gain (Loss), instruments still held, asset	79,000	[2]	279,000	[2]
Balance Asset Value	380,000		378,000
Consolidated Funds | Portfolio Funds, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	155,674,000		182,920,000
Asset, Transfers In	0		0
Asset, Transfers Out	0		0
Purchases/(covers)	0		0
(Sales)/short buys	(28,466,000)		(33,504,000)
Realized and unrealized gains (losses), asset	11,045,000		6,258,000
Change in Unrealized Gain (Loss), instruments still held, asset	9,996,000	[2]	10,984,000	[2]
Balance Asset Value	138,253,000		155,674,000
Consolidated Funds | Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value	4,842,000		14,124,000
Asset, Transfers In	0		0
Asset, Transfers Out	0		0
Purchases/(covers)	0		0
(Sales)/short buys	(4,711,000)		(13,377,000)
Realized and unrealized gains (losses), asset	362,000		4,095,000
Change in Unrealized Gain (Loss), instruments still held, asset	(3,897,000)	[2]	(7,781,000)	[2]
Balance Asset Value	493,000		4,842,000
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value	0
Liability, Transfers In	0
Liability, Transfers Out	0
Liability, Purchases	(35,710,000)
Liability, Sales	0
Realized and unrealized gains (losses), liability	1,097,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	1,097,000	[2]
Balance Liability Value	36,807,000
Warrants and Rights, sold not yet purchased
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value			3,000
Liability, Transfers In			0
Liability, Transfers Out			0
Liability, Purchases			0
Liability, Sales			0
Realized and unrealized gains (losses), liability			(3,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities			0	[2]
Balance Liability Value			0
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value	6,937,000		8,116,000
Liability, Transfers In	0		0
Liability, Transfers Out	0		0
Liability, Purchases	(21,000)		(779,000)
Liability, Sales	(820,000)		0
Realized and unrealized gains (losses), liability	(2,055,000)		(400,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	0	[2]	0	[2]
Balance Liability Value	$ 4,083,000		$ 6,937,000

[1] The company completed an initial public offering.

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

[3] The security was acquired through an acquisition (See Note 2).

[4] The investment was transferred into level 3 due to the Company's commitment as part of its long term extension of its partnership