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Investment Portfolio - Narrative (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Fair value of investment	$ 129,700,000
Securities held in Consolidated Funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Investments	65,106,741	$ 57,355,471
Total | Securities held in Consolidated Funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Investments	41,900,000	42,600,000
Redeemable Noncontrolling Interest | Securities held in Consolidated Funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Investments	$ 23,200,000	$ 14,700,000

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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