Quarterly report pursuant to Section 13 or 15(d)

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

v3.20.2
Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail)
3 Months Ended 9 Months Ended
Sep. 30, 2020
USD ($)
Office
Sep. 30, 2019
USD ($)
Office
Sep. 30, 2020
USD ($)
Office
Sep. 30, 2019
USD ($)
Office
Jun. 30, 2020
USD ($)
Jan. 01, 2020
USD ($)
Dec. 31, 2019
USD ($)
Jun. 30, 2019
USD ($)
Dec. 31, 2018
USD ($)
Accounting Policies [Line Items]                  
Commission's receivable settled period     10 days            
Number of offices | Office     83            
Cumulative effect adjustment, net $ (521,034,000) $ (472,100,000) $ (521,034,000) $ (472,100,000) $ (512,913,000)   $ (494,907,000) $ (450,513,000) $ (409,574,000)
Credit Agreement [Member]                  
Accounting Policies [Line Items]                  
Line of credit $ 0   $ 0            
cumulative effect, period of adoption, adjustment [Member]                  
Accounting Policies [Line Items]                  
Cumulative effect adjustment, net             $ 33,000    
Transaction Risk [Member]                  
Accounting Policies [Line Items]                  
Concentration risk percentage 0.00% 0.00% 0.00% 0.00%          
Transaction Risk [Member] | Total revenues [Member]                  
Accounting Policies [Line Items]                  
Concentration risk percentage 10.00% 10.00% 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% 10.00% 10.00%          
Number of offices | Office 0 0 0 0          
Accounting Standards Update 2016-13 [Member] | cumulative effect, period of adoption, adjustment [Member]                  
Accounting Policies [Line Items]                  
Cumulative effect adjustment, net           $ 33,000      
Minimum [Member] | Loan To Investment Sales and Financing Professionals [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 To Investment Sales and Financing Professionals [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% 2.00% 1.00%