Quarterly report pursuant to Section 13 or 15(d)

Broker-Dealers and Clearing Organizations and Other Receivables - Additional Information (Detail)

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Broker-Dealers and Clearing Organizations and Other Receivables - Additional Information (Detail) - USD ($)
Sep. 30, 2016
Sep. 09, 2016
Dec. 31, 2015
Brokers And Dealers [Line Items]      
Receivables from Brokers-Dealers and Clearing Organizations $ 1,607,000   $ 0
Allowance for Doubtful Accounts Receivable $ 0   $ 0
Forgivable Loan Receivable [Member]      
Brokers And Dealers [Line Items]      
Accounts Receivable, Net   $ 1,800,000  
Broker -Dealers And clearing Organisation [Member]      
Brokers And Dealers [Line Items]      
Receivables from Brokers-Dealers and Clearing Organizations   1,600,000  
Allowance for Doubtful Accounts Receivable   782,000  
Broker -Dealers And clearing Organisation [Member] | Forgivable Loan Receivable [Member]      
Brokers And Dealers [Line Items]      
Accounts Receivable, Net   1,800,000  
Broker -Dealers And clearing Organisation [Member] | Other Receivable [Member]      
Brokers And Dealers [Line Items]      
Accounts Receivable, Net   $ 3,100,000