Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail)
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
Office
Jun. 30, 2017
Office
Jun. 30, 2018
USD ($)
Office
Segment
Jun. 30, 2017
Office
Dec. 31, 2017
USD ($)
Accounting Policies [Line Items]          
Commission's receivable settled period 10 days        
Number of reporting units | Segment     1    
Finite-lived intangible asset, amortization method     Straight-line    
Marketable securities, available for sale $ 117,403,000   $ 117,403,000   $ 125,659,000
Accounting Standards Update 2018-02 [Member]          
Accounting Policies [Line Items]          
Reclassification of stranded tax effects from accumulated other comprehensive income to retained earnings     13,000    
Accounting Standards Update 2016-02 [Member]          
Accounting Policies [Line Items]          
Operating lease obligations $ 88,300,000   $ 88,300,000    
Customer Concentration Risk [Member] | Total revenues [Member]          
Accounting Policies [Line Items]          
Concentration risk percentage 10.00% 10.00% 10.00% 10.00%  
Customer Concentration Risk [Member] | Commissions receivable [Member]          
Accounting Policies [Line Items]          
Concentration risk percentage 10.00% 10.00% 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  
Maximum [Member]          
Accounting Policies [Line Items]          
Finite-lived intangible asset, useful life     6 years    
Minimum [Member]          
Accounting Policies [Line Items]          
Finite-lived intangible asset, useful life     1 year    
Capitalization of Internal Labor [Member] | Maximum [Member]          
Accounting Policies [Line Items]          
Property and equipment, estimated useful life     7 years    
Capitalization of Internal Labor [Member] | Minimum [Member]          
Accounting Policies [Line Items]          
Property and equipment, estimated useful life     3 years    
Average AA Credit Rating [Member] | Accounting Standards Update 2016-13 [Member]          
Accounting Policies [Line Items]          
Marketable securities, available for sale $ 117,400,000   $ 117,400,000    
Impairment write-downs marketable securities, available for sale     $ 0    
International Revenues [Member] | Maximum [Member] | Geographic Concentration Risk [Member] | Total revenues [Member]          
Accounting Policies [Line Items]          
Concentration risk percentage 1.00% 1.00% 1.00% 1.00%