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Investment Portfolio - Summary of Market Value of Investments (Detail) - USD ($) | Dec. 31, 2016 | Dec. 31, 2015
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Investment Holdings [Line Items] |  |
Seed capital equity method investments | $ 36,457,449 | $ 11,284,109
Deferred compensation plan assets | 14,182,470 | 7,961,412
Total Investment Portfolio | 108,015,635 | 52,490,820
Securities held in Consolidated Funds |  |
Investment Holdings [Line Items] |  |
Trading Investments | 57,355,471 | 0
Securities held in Consolidated Funds | Total |  |
Investment Holdings [Line Items] |  |
Trading Investments | 42,600,000 |
Securities held in Consolidated Funds | Redeemable Noncontrolling Interest |  |
Investment Holdings [Line Items] |  |
Trading Investments | 14,700,000 |
Company Sponsored Investments |  |
Investment Holdings [Line Items] |  |
Trading Investments | $ 20,245 | $ 33,245,299

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