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Investment Portfolio - Summary of Market Value of Investments (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Investment Holdings [Line Items]
Seed capital equity method investments	$ 27,952,788
Deferred compensation investments	13,369,919
Total Investment portfolio	87,047,844	$ 52,490,820
Securities held in Consolidated Funds
Investment Holdings [Line Items]
Trading investments	45,704,913
Securities held in Consolidated Funds | Total
Investment Holdings [Line Items]
Trading investments	41,600,000
Securities held in Consolidated Funds | Redeemable Noncontrolling Interest
Investment Holdings [Line Items]
Trading investments	4,100,000
Securities held in Consolidated Funds | Fair Value, Measurements, Recurring [Member]
Investment Holdings [Line Items]
Trading investments	45,704,913
Seed capital investments
Investment Holdings [Line Items]
Trading investments	20,224
Seed capital investments | Fair Value, Measurements, Recurring [Member]
Investment Holdings [Line Items]
Trading investments	$ 20,224

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