Quarterly report pursuant to Section 13 or 15(d)

Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail)

v3.20.1
Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail)
 3 Months Ended
Jan. 01, 2020
USD ($)
Mar. 31, 2020
USD ($)
Office
Mar. 31, 2019
Office
Dec. 31, 2019
USD ($)
Accounting Policies [Line Items]        
Commission's receivable settled period   10 days    
Number of offices | Office   82    
Allowance for commissions receivable | $   $ 0   $ 0
Transaction Risk [Member]        
Accounting Policies [Line Items]        
Concentration risk percentage   0.00% 0.00%  
Transaction Risk [Member] | Total revenues [Member]        
Accounting Policies [Line Items]        
Concentration risk percentage   10.00% 10.00%  
Transaction Risk [Member] | Commissions receivable, net [Member]        
Accounting Policies [Line Items]        
Concentration risk percentage   10.00%    
Geographic Concentration Risk [Member] | Total revenues [Member]        
Accounting Policies [Line Items]        
Concentration risk percentage   10.00% 10.00%  
Number of offices | Office   1 0  
Accounting Standards Update 2016-13 [Member]        
Accounting Policies [Line Items]        
Cumulative effect adjustment, net | $ $ 33,000,000      
Minimum [Member] | Loan [Member]        
Accounting Policies [Line Items]        
Loans to Investment Sales and Financing Professionals, Repayment Term   1 year    
Minimum [Member] | Advances To Investment Sales And Financing Professionals [Member]        
Accounting Policies [Line Items]        
Advances to Investment Sales and Financing Professionals, Repayment Term   5 years    
Maximum [Member] | Loan [Member]        
Accounting Policies [Line Items]        
Loans to Investment Sales and Financing Professionals, Repayment Term   7 years    
Maximum [Member] | Advances To Investment Sales And Financing Professionals [Member]        
Accounting Policies [Line Items]        
Advances to Investment Sales and Financing Professionals, Repayment Term   10 years    
Maximum [Member] | Geographic Concentration Risk [Member] | Total revenues [Member] | International Revenues [Member]        
Accounting Policies [Line Items]        
Concentration risk percentage   2.00% 1.00%