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Investment Portfolio - Summary of Market Value of Investments (Detail) - USD ($) | Mar. 31, 2016 | Dec. 31, 2015
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Investment Holdings [Line Items] |  |
Equity method investments | $ 17,846,201 |
Deferred compensation investments | 12,520,233 |
Total Investment portfolio | 56,189,839 | $ 52,490,820
Equity securities held in consolidated ETF |  |
Investment Holdings [Line Items] |  |
Trading investments | 16,394,754 |
Equity securities held in consolidated ETF | Total |  |
Investment Holdings [Line Items] |  |
Trading investments | 12,100,000 |
Equity securities held in consolidated ETF | Redeemable Noncontrolling Interest |  |
Investment Holdings [Line Items] |  |
Trading investments | 4,300,000 |
Seed capital investments |  |
Investment Holdings [Line Items] |  |
Trading investments | $ 9,428,651 |

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