The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

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Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

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The sum of the realized and unrealized net gain (loss) on trading securities during the period.

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This item represents the gain (loss) realized during the period from the sale of trading securities.

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Amount of unrealized holding gain (loss) recognized in the income statement for investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Summary of Investment Holdings [Line Items]
Investments owned	$ 728,751us-gaap_InvestmentOwnedAtFairValue		$ 763,475us-gaap_InvestmentOwnedAtFairValue
Long-term incentive compensation obligations	80,546		98,779
Net Realized and Unrealized Gain (Loss) on Trading Securities [Abstract]
Net gains recognized during the period	6,784	14,812
Less: net gains recognized during the period on trading securities sold during the period	6,047	4,404
Unrealized gains recognized during the period on trading securities held	737	10,408
Consolidated Private Equity Fund [Member]
Summary of Investment Holdings [Line Items]
Investments owned	34,130		32,604
Percentage of seed capital (in hundredths)	10.00%		10.00%
Private Equity [Member]
Summary of Investment Holdings [Line Items]
Investments owned	48,724		48,734
Available-for-Sale Investments [Member]
Summary of Investment Holdings [Line Items]
Investments owned	6,442		6,172
Trading Investments [Member] \| Long-term Incentive Compensation-Related [Member]
Summary of Investment Holdings [Line Items]
Investments owned	60,594		74,095
Trading Investments [Member] \| Equities [Member]
Summary of Investment Holdings [Line Items]
Investments owned	59,508		79,720
Trading Investments [Member] \| Exchange Traded Options [Member]
Summary of Investment Holdings [Line Items]
Investments owned	6,767		22,290
Trading Investments [Member] \| U.S Treasury Bills [Member]
Summary of Investment Holdings [Line Items]
Investments owned	28,995		28,982
Trading Investments [Member] \| Seed Capital [Member]
Summary of Investment Holdings [Line Items]
Investments owned	425,805		400,746
Investments in Limited Partnership Hedge Funds [Member] \| Long-term Incentive Compensation-Related [Member]
Summary of Investment Holdings [Line Items]
Investments owned	19,952		24,684
Investments in Limited Partnership Hedge Funds [Member] \| Seed Capital [Member]
Summary of Investment Holdings [Line Items]
Investments owned	26,366		33,951
Other Investment [Member]
Summary of Investment Holdings [Line Items]
Investments owned	$ 11,468		$ 11,497