Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.2
Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail)
 3 Months Ended 6 Months Ended
Jun. 30, 2019
USD ($)
Office
Jun. 30, 2018
Office
Jun. 30, 2019
USD ($)
Office
Jun. 30, 2018
Office
Jan. 01, 2019
USD ($)
Dec. 31, 2018
USD ($)
Accounting Policies [Line Items]            
Commission's receivable settled period     10 days      
Number of offices | Office     80      
Operating lease right-of-use assets $ 93,090,000   $ 93,090,000     $ 0
Operating lease liabilities 84,829,000   84,829,000      
Prepaid Rent Reclassified to Other Assets, Current 6,233,000   6,233,000     6,368,000
Marketable securities, available for sale $ 199,238,000   $ 199,238,000     $ 220,645,000
Customer Concentration Risk [Member] | Total revenues [Member]            
Accounting Policies [Line Items]            
Concentration risk percentage     10.00% 10.00%    
Customer Concentration Risk [Member] | Commissions receivable [Member]            
Accounting Policies [Line Items]            
Concentration risk percentage     10.00% 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 2016-02 [Member]            
Accounting Policies [Line Items]            
Operating lease right-of-use assets         $ 76,700,000  
Operating lease liabilities         76,700,000  
Prepaid Rent Reclassified to Other Assets, Current         462,000  
Accounting Standards Update 2016-02 [Member] | Deferred rent reclassified to Operating Lease ROU Asset [Member]            
Accounting Policies [Line Items]            
Operating lease right-of-use assets         5,600,000  
Accounting Standards Update 2016-02 [Member] | Prepaid rent reclassified to Operating Lease ROU Asset [Member]            
Accounting Policies [Line Items]            
Operating lease right-of-use assets         $ 13,400,000  
Accounting Standards Update 2018-13 [Member]            
Accounting Policies [Line Items]            
Contingent consideration liability $ 2,900,000   $ 2,900,000      
Average AA+ Credit Rating [Member] | Accounting Standards Update 2016-13 [Member]            
Accounting Policies [Line Items]            
Marketable securities, available for sale $ 199,200,000   $ 199,200,000      
Maximum [Member] | Geographic Concentration Risk [Member] | Total revenues [Member] | International Revenues [Member]            
Accounting Policies [Line Items]            
Concentration risk percentage 1.00% 1.00% 1.00% 1.00%