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Investment Portfolio - Narrative (Detail) - USD ($) | Mar. 31, 2017 | Dec. 31, 2016
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Investments, Debt and Equity Securities [Abstract] |  |
Fair value of investment | $ 117,400,000 |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Deferred compensation investments | 18,683,617 | $ 14,182,470
Trading Securities |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Deferred compensation investments | 12,800,000 | 9,300,000
Equity Method Investments |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Deferred compensation investments | 5,900,000 | 4,900,000
Securities held in Consolidated Funds |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Trading Investments | 61,452,815 | 57,355,471
Total | Securities held in Consolidated Funds |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Trading Investments | 43,900,000 | 42,600,000
Redeemable Noncontrolling Interest | Securities held in Consolidated Funds |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Trading Investments | $ 17,600,000 | $ 14,700,000

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