Annual report pursuant to Section 13 and 15(d)

Accounting Policies - Additional Information (Detail)

v3.6.0.2
Accounting Policies - Additional Information (Detail)
 12 Months Ended
Jan. 01, 2017
USD ($)
Dec. 31, 2016
USD ($)
Office
Financial_Institutions
Segments
Dec. 31, 2015
USD ($)
Office
Dec. 31, 2014
USD ($)
Office
Accounting Policies [Line Items]        
Number of financial institutions | Financial_Institutions   4    
Allowance for commissions receivable   $ 0 $ 0  
Other-than-temporary impairment   0 0  
Advertising costs   $ 1,200,000 1,100,000 $ 965,000
Income tax benefit realized, percentage   50.00%    
Uncertain tax positions   $ 0 0  
Commission's receivable settled period   10 days    
Number of reportable segments | Segments   1    
Operating lease obligations   $ 76,335,000    
Marketable securities, available for sale   $ 104,929,000 $ 134,255,000  
Employee Stock Purchase Plan [Member]        
Accounting Policies [Line Items]        
Length of purchase intervals   6 months    
Expected dividend yield   0.00%    
Forfeiture rate   0.00%    
Payment of dividend   $ 0    
Level 3 [Member]        
Accounting Policies [Line Items]        
Investments   0    
Recent Accounting Pronouncement [Member]        
Accounting Policies [Line Items]        
Operating lease obligations   76,335,000    
Marketable securities, available for sale   $ 104,929,000    
Recent Accounting Pronouncement [Member] | Subsequent Event [Member]        
Accounting Policies [Line Items]        
Cumulative effect adjustments, net of tax $ 52,000      
Customer Concentration Risk [Member] | Total revenues [Member]        
Accounting Policies [Line Items]        
Concentration risk percentage   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%
Geographic Concentration Risk [Member] | Total revenues [Member]        
Accounting Policies [Line Items]        
Concentration risk percentage   10.00% 10.00% 10.00%
Number of offices | Office   0 0 0
Maximum [Member]        
Accounting Policies [Line Items]        
Property and equipment, estimated useful lives   7 years    
Minimum [Member]        
Accounting Policies [Line Items]        
Property and equipment, estimated useful lives   3 years