Fair Value Measurements for Operating Entities and Consolidated Funds - Assets and Liabilities at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	$ 400,945		$ 334,251
Operating Companies [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	4,808
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	856,411		788,977
Liabilities at fair value	401,778		335,008
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	598,745		491,607
Liabilities at fair value	392,906		333,337
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	231,177		274,942
Liabilities at fair value	8,869		1,671
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	26,489		22,428
Liabilities at fair value	3		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	225,679		165,197
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	225,679		165,197
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	7,985		1,529
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	7,985		1,529
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	142,314		123,877
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	142,314		123,875
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	0		2
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	0	0	0	0	401	0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities sold, not yet purchased, at fair value	3	0	0	0	0	0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Futures [Member] | Derivative Liabilities [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	19		617
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Futures [Member] | Derivative Liabilities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	19		617
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Futures [Member] | Derivative Liabilities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Futures [Member] | Derivative Liabilities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Equity Swap [Member] | Derivative Liabilities [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			140
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Equity Swap [Member] | Derivative Liabilities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Equity Swap [Member] | Derivative Liabilities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			140
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Equity Swap [Member] | Derivative Liabilities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Forward Contracts [Member] | Derivative Liabilities [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	814
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Forward Contracts [Member] | Derivative Liabilities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Forward Contracts [Member] | Derivative Liabilities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	814
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Forward Contracts [Member] | Derivative Liabilities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Options [Member] | Derivative Liabilities [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	24,964		43,648
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Options [Member] | Derivative Liabilities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	24,894		43,648
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Options [Member] | Derivative Liabilities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	70		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Options [Member] | Derivative Liabilities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Derivative Liabilities [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	3
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Derivative Liabilities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Derivative Liabilities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Derivative Liabilities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	3
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	206,123		182,868
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	206,123		182,868
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Convertible Bonds [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	12,633		18,130
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Convertible Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Convertible Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	12,633		18,130
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Convertible Bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	191,840		231,864
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	191,840		231,864
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	353,840		250,380
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	352,841		248,598
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	40		713
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	959	1,079	1,069	953	490	334
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	3,494		2,759
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	650		1,225
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Warrants and Rights [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	2,844	3,316	1,534	3,534	2,902	1,977
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	2,816		3,214
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	2,816		3,214
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Futures [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	236		172
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Futures [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	236		172
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Futures [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Futures [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Equity Swap [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets			635
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Equity Swap [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets			0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Equity Swap [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets			635
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Equity Swap [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets			0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Forward Contracts [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	16
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Forward Contracts [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Forward Contracts [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	16
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Forward Contracts [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Options [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	36,520		55,699
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Options [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	36,079		55,530
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Options [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	441		169
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Assets [Member] | Options [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Portfolio Funds [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	46,083		40,350
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Portfolio Funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Portfolio Funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	26,207		23,431
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Portfolio Funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	19,876	19,012	16,919	17,744	17,660	17,081
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Investments [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	2,079		2,353
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Investments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Investments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Investments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	2,079	2,579	2,353	2,289	2,102	1,882
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Lehman Claim [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	731		553
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Lehman Claim [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Lehman Claim [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Operating Companies [Member] | Fair Value, Measurements, Recurring [Member] | Lehman Claim [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	731	574	553	501	501	313
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	230,152		235,154
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	1,602		2,006
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	12,505		12,406
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	216,045		220,742
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	1,602		2,006
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	1,602		2,006
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | US Government Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		401
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		401
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	632		3,927
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	632		3,927
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Portfolio Funds [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	221,380		221,480
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Portfolio Funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Portfolio Funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	11,873		8,078
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Portfolio Funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	209,507	215,815	213,402	239,588	260,443	311,242
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Lehman Claim [Member] | Total Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	6,538		7,340
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Lehman Claim [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Lehman Claim [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0		0
Consolidated Funds [Member] | Fair Value, Measurements, Recurring [Member] | Lehman Claim [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	$ 6,538	$ 5,346	$ 7,340	$ 7,320	$ 7,193	$ 6,243