Investment Portfolio - Narrative (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Fair value of investment	$ 117,400,000
Schedule of Trading Securities and Other Trading Assets [Line Items]
Deferred compensation investments	18,683,617	$ 14,182,470
Trading Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Deferred compensation investments	12,800,000	9,300,000
Equity Method Investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Deferred compensation investments	5,900,000	4,900,000
Securities held in Consolidated Funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Investments	61,452,815	57,355,471
Total \| Securities held in Consolidated Funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Investments	43,900,000	42,600,000
Redeemable Noncontrolling Interest \| Securities held in Consolidated Funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Investments	$ 17,600,000	$ 14,700,000

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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