Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) (Level 3, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Operating Companies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, end of period	$ 8,510
Operating Companies | Lehman Claim
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, end of period	660
Fair Value, Measurements, Recurring | Operating Companies | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	2,332		250
Transfers In	0		0
Transfers Out	0		0
Purchases	0
Sales	0
Realized gains (losses)	0
Unrealized gains (losses)	0		2
Investments at fair value, end of period	2,332		252
Fair Value, Measurements, Recurring | Operating Companies | Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	2,549		819
Transfers In	0		0
Transfers Out	0		0
Purchases	0		0
Sales	(265)		(6)
Realized gains (losses)	260		6
Unrealized gains (losses)	(266)		8
Investments at fair value, end of period	2,278		827
Fair Value, Measurements, Recurring | Operating Companies | Corporate Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	515
Transfers In	0
Transfers Out	0
Purchases	2,735
Sales	(3,346)
Realized gains (losses)	(914)
Unrealized gains (losses)	1,010
Investments at fair value, end of period	0
Fair Value, Measurements, Recurring | Operating Companies | Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	1,713		1,534
Transfers In	290	[1]	0
Transfers Out	0		(88)	[2]
Purchases	166		257
Sales	(110)		(65)
Realized gains (losses)	0		56
Unrealized gains (losses)	1,184		1,622
Investments at fair value, end of period	3,243		3,316
Fair Value, Measurements, Recurring | Operating Companies | Warrants and Rights, sold not yet purchased
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	3		0
Transfers In	0		0
Transfers Out	0		(1,004)
Covers			(302)
Short buys			973
Purchases	0
Sales	0
Realized gains (losses)	0		(35)
Unrealized gains (losses)	0		368
Investments at fair value, end of period	3		0
Fair Value, Measurements, Recurring | Operating Companies | Portfolio Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	25,670		16,919
Transfers In	0		0
Transfers Out	0		0
Purchases	3,590		1,622
Sales	(3,876)		(529)
Realized gains (losses)	8		6
Unrealized gains (losses)	167		995
Investments at fair value, end of period	25,559		19,013
Fair Value, Measurements, Recurring | Operating Companies | Real Estate Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	1,864		2,353
Transfers In	0		0
Transfers Out	0		0
Purchases			152
Sales	0		0
Realized gains (losses)	0		0
Unrealized gains (losses)	11		74
Investments at fair value, end of period	1,875		2,579
Fair Value, Measurements, Recurring | Operating Companies | Lehman Claim
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	706		553
Transfers In	0		0
Transfers Out	0		0
Purchases	0		0
Sales	0		0
Realized gains (losses)	0		0
Unrealized gains (losses)	(46)		21
Investments at fair value, end of period	660		574
Fair Value, Measurements, Recurring | Consolidated Funds | Portfolio Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	182,920		213,402
Transfers In	0		16,769	[3]
Transfers Out	0		(17,151)	[3]
Purchases	0		415
Sales	(7,031)		(2,888)
Realized gains (losses)	222		214
Unrealized gains (losses)	2,246		5,596
Investments at fair value, end of period	178,357		216,357
Fair Value, Measurements, Recurring | Consolidated Funds | Lehman Claim
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value, beginning of period	14,124		7,340
Transfers In	0		0
Transfers Out	0		0
Purchases	0		0
Sales	(1,449)		(2,291)
Realized gains (losses)	1,360		1,914
Unrealized gains (losses)	1,105		(1,617)
Investments at fair value, end of period	$ 15,140		$ 5,346

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

[2] The security was listed on an exchange subsequent to a private funding.

[3] Change in consolidated funds.