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Significant Accounting Policies - Mutual Fund Administration Revenue (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Revenue from External Customer [Line Items] |  |  |
Total revenue | $ 145,627,748 | $ 145,201,729 | $ 136,103,075
Administration revenue, gross |  |  |
Revenue from External Customer [Line Items] |  |  |
Total revenue | 24,463,538 | 26,219,881 | 26,664,635
12b-1/Service Fees And Commissions |  |  |
Revenue from External Customer [Line Items] |  |  |
Total revenue | 0 | 0 | 6,360,400
Expenses | 0 | 0 | (5,660,430)
Fund related expense |  |  |
Revenue from External Customer [Line Items] |  |  |
Expenses | (14,183,370) | (13,748,445) | (12,937,067)
Revenue, net of related expenses |  |  |
Revenue from External Customer [Line Items] |  |  |
Total revenue | 10,280,168 | 12,471,436 | 14,427,538
Broker Commission |  |  |
Revenue from External Customer [Line Items] |  |  |
Total revenue | 332,680 | 416,614 | 691,228
Expenses | (302,905) | (374,783) | (660,840)
Financing activity, net |  |  |
Revenue from External Customer [Line Items] |  |  |
Total revenue | 29,775 | 41,831 | 30,388
Mutual fund administration revenue, net |  |  |
Revenue from External Customer [Line Items] |  |  |
Total revenue | $ 10,309,943 | $ 12,513,267 | $ 14,457,926

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