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 ($)
$ in Thousands
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Sep. 30, 2016
Brokers And Dealers [Line Items]        
Receivables from Brokers-Dealers and Clearing Organizations $ 7,395   $ 3,357  
Allowance for Doubtful Accounts Receivable $ 1,300   $ 100  
Accounts Receivable, Net   $ 5,200   $ 5,400
Broker -Dealers And clearing Organisation [Member]        
Brokers And Dealers [Line Items]        
Receivables from Brokers-Dealers and Clearing Organizations   7,400   3,400
Allowance for Doubtful Accounts Receivable   $ 500   $ 700