Annual report pursuant to Section 13 and 15(d)

Notes Receivable from Financial Advisors (Detail)

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Notes Receivable from Financial Advisors (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Allowance for doubtful accounts $ 416 $ 371
Minimum    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loan amortized over forgiveness period 3 years  
Maximum    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage bearing variable interest rate 10.00%  
Loan amortized over forgiveness period 5 years