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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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