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Significant Accounting Policies - Narrative (Detail) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2016 USD ($) | Sep. 30, 2015 USD ($) | Sep. 30, 2016 USD ($) Segment | Sep. 30, 2015 USD ($) | Dec. 31, 2015 USD ($)
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Cumulative-effect adjustment from the adoption of ASU 2015-02 (Note 2) |  |  | $ 4,031,756 | $ 0 |
Number of business segment | Segment |  |  | 1 |  |
Allowance for doubtful accounts | $ 0 |  | $ 0 |  | $ 0
Accounts receivable, related parties | 9,400,000 |  | 9,400,000 |  | 9,200,000
Transfers between fair value levels | 0 |  | $ 0 |  | 0
Client performance period |  |  | 5 years |  |
Advance commissions amortization period |  |  | 12 months |  |
Liability for uncertain tax positions | 0 |  | $ 0 |  | $ 0
Securities held in Consolidated Funds |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Trading Investments | 45,704,913 |  | 45,704,913 |  |
Money Market Funds | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Cash equivalents | 56,100,000 |  | 56,100,000 |  |
Incentive Fees Method One [Member] |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Performance incentive fees |  |  | 0 | 0 |
Investment Advisory Services [Member] |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Revenue from related parties | 22,900,000 | $ 20,700,000 | 65,200,000 | 59,200,000 |
Mutual fund administrative services [Member] |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Revenue from related parties | 3,000,000 | $ 3,000,000 | 8,800,000 | $ 9,600,000 |
Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Cash equivalents | 56,074,210 |  | 56,074,210 |  |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Cash equivalents | 56,074,210 |  | 56,074,210 |  |
Fair Value, Measurements, Recurring [Member] | Securities held in Consolidated Funds |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Trading Investments | 45,704,913 |  | 45,704,913 |  |
Fair Value, Measurements, Recurring [Member] | Securities held in Consolidated Funds | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Trading Investments | 17,517,463 |  | 17,517,463 |  |
Total | Securities held in Consolidated Funds |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Trading Investments | 41,600,000 |  | 41,600,000 |  |
Redeemable Noncontrolling Interest |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Cumulative-effect adjustment from the adoption of ASU 2015-02 (Note 2) |  |  | 4,031,756 |  |
Redeemable Noncontrolling Interest | Securities held in Consolidated Funds |  |  |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Trading Investments | $ 4,100,000 |  | $ 4,100,000 |  |

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