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Investment Portfolio - Summary of Market Value of Investments (Detail) - USD ($) | Sep. 30, 2017 | Dec. 31, 2016
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Investment Holdings [Line Items] |  |
Company sponsored equity method investments | $ 29,753,573 | $ 41,338,046
Total Investment portfolio | 129,743,381 | 108,015,635
Securities held in Consolidated Funds |  |
Investment Holdings [Line Items] |  |
Trading investments | 65,106,741 | 57,355,471
Securities held in Consolidated Funds | Parent |  |
Investment Holdings [Line Items] |  |
Trading investments | 41,900,000 | 42,600,000
Securities held in Consolidated Funds | Redeemable Noncontrolling Interest |  |
Investment Holdings [Line Items] |  |
Trading investments | 23,200,000 | 14,700,000
Company sponsored investments |  |
Investment Holdings [Line Items] |  |
Trading investments | $ 34,883,067 | $ 9,322,118

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