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Significant Accounting Policies - Mutual Fund Administration Gross and Net Revenue (Detail) - USD ($) | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Revenue from External Customer [Line Items] |  |
Revenue | $ 32,579,373 | $ 37,782,002
Administrative revenue, gross |  |
Revenue from External Customer [Line Items] |  |
Revenue | 5,402,728 | 6,607,337
Fund related expense |  |
Revenue from External Customer [Line Items] |  |
Expenses | 3,349,541 | 3,468,325
Revenue, net of related expense |  |
Revenue from External Customer [Line Items] |  |
Revenue | 2,053,187 | 3,139,012
Broker Commission |  |
Revenue from External Customer [Line Items] |  |
Revenue | 65,212 | 96,478
Expenses | 51,744 | 84,778
Financing activity, net |  |
Revenue from External Customer [Line Items] |  |
Revenue | 13,468 | 11,700
Mutual fund administration, net |  |
Revenue from External Customer [Line Items] |  |
Revenue | $ 2,066,655 | $ 3,150,712

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