Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of Investment Holdings [Line Items]
Investments owned	$ 795,294,000	$ 756,555,000
Deferred compensation obligations	176,370,000	298,705,000
Trading [Abstract]
Proceeds from sales of available-for-sale investments	3,500,000	4,300,000	6,900,000
Realized gains from sales of available-for-sale investments	100,000	500,000	0
Realized losses from our sales of available-for-sale investments	100,000	400,000	2,500,000
Consolidated Private Equity [Member]
Summary of Investment Holdings [Line Items]
Investments owned	58,749,000	101,360,000
Private Equity [Member]
Summary of Investment Holdings [Line Items]
Investments owned	35,726,000	17,803,000
Available-For-Sale Investments [Member]
Summary of Investment Holdings [Line Items]
Investments owned	13,883,000	16,588,000
Available-for-sale [Abstract]
Amortized Cost	13,610,000	15,962,000
Gross Unrealized Gains	622,000	1,662,000
Gross Unrealized Losses	(349,000)	(1,036,000)
Fair Value	13,883,000	16,588,000
Available-For-Sale Investments [Member] | Equity Investments [Member]
Available-for-sale [Abstract]
Amortized Cost	6,753,000	9,695,000
Gross Unrealized Gains	489,000	1,380,000
Gross Unrealized Losses	(342,000)	(1,023,000)
Fair Value	6,900,000	10,052,000
Available-For-Sale Investments [Member] | Fixed Income Investments [Member]
Available-for-sale [Abstract]
Amortized Cost	6,857,000	6,267,000
Gross Unrealized Gains	133,000	282,000
Gross Unrealized Losses	(7,000)	(13,000)
Fair Value	6,983,000	6,536,000
Trading Investments [Member]
Trading [Abstract]
Amortized Cost	547,429,000	476,965,000
Gross Unrealized Gains	9,434,000	37,105,000
Gross Unrealized Losses	(45,864,000)	(8,460,000)
Fair value	510,999,000	505,610,000
Trading Investments [Member] | Deferred Compensation-Related [Member]
Summary of Investment Holdings [Line Items]
Investments owned	135,832,000	239,787,000
Trading Investments [Member] | US Treasury Bill Securities [Member]
Summary of Investment Holdings [Line Items]
Investments owned	37,998,000	52,975,000
Trading Investments [Member] | Seed Money [Member]
Summary of Investment Holdings [Line Items]
Investments owned	278,932,000	177,589,000
Trading Investments [Member] | Other Trading Investments [Member]
Summary of Investment Holdings [Line Items]
Investments owned	58,237,000	35,259,000
Trading Investments [Member] | Equity Investments [Member]
Trading [Abstract]
Amortized Cost	375,287,000	269,529,000
Gross Unrealized Gains	5,959,000	34,211,000
Gross Unrealized Losses	(41,938,000)	(6,259,000)
Fair value	339,308,000	297,481,000
Trading Investments [Member] | Fixed Income Investments [Member]
Trading [Abstract]
Amortized Cost	172,142,000	207,436,000
Gross Unrealized Gains	3,475,000	2,894,000
Gross Unrealized Losses	(3,926,000)	(2,201,000)
Fair value	171,691,000	208,129,000
Investments In Limited Partnership Hedge Funds [Member] | Deferred Compensation-Related [Member]
Summary of Investment Holdings [Line Items]
Investments owned	40,538,000	58,918,000
Investments In Limited Partnership Hedge Funds [Member] | Seed Money and Other [Member]
Summary of Investment Holdings [Line Items]
Investments owned	123,920,000	47,735,000
Other Investment [Member]
Summary of Investment Holdings [Line Items]
Investments owned	$ 11,479,000	$ 8,541,000