Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail)
 3 Months Ended
Mar. 31, 2019
USD ($)
Office
Mar. 31, 2018
Office
Jan. 01, 2019
USD ($)
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 $ 83,913,000     $ 0
Operating lease liabilities 75,852,000      
Prepaid Rent Reclassified to Other Assets, Current 6,031,000     6,368,000
Marketable securities, available for sale $ 196,103,000     $ 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%    
Number of offices | Office 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      
Average AA+ Credit Rating [Member] | Accounting Standards Update 2016-13 [Member]        
Accounting Policies [Line Items]        
Marketable securities, available for sale $ 196,100,000      
Maximum [Member] | Geographic Concentration Risk [Member] | Total revenues [Member] | International Revenues [Member]        
Accounting Policies [Line Items]        
Concentration risk percentage 1.00% 1.00%