Annual report pursuant to Section 13 and 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 ($)
Dec. 31, 2016
Sep. 30, 2016
Dec. 31, 2015
Brokers And Dealers [Line Items]      
Receivables from Brokers-Dealers and Clearing Organizations $ 3,357,000   $ 0
Allowance for Doubtful Accounts Receivable 0   $ 0
Accounts Receivable, Net, Total $ 71,800    
Broker -Dealers And clearing Organisation [Member]      
Brokers And Dealers [Line Items]      
Receivables from Brokers-Dealers and Clearing Organizations   $ 3,400,000  
Allowance for Doubtful Accounts Receivable   700,000  
Broker -Dealers And clearing Organisation [Member] | Other Receivable [Member]      
Brokers And Dealers [Line Items]      
Accounts Receivable, Net, Total   $ 5,400,000