Quarterly report pursuant to Section 13 or 15(d)

Description of Business and Basis of Presentation - Additional Information (Detail)

v3.7.0.1
Description of Business and Basis of Presentation - Additional Information (Detail)
3 Months Ended 6 Months Ended
Jan. 01, 2017
USD ($)
Jun. 30, 2017
USD ($)
Office
Jun. 30, 2016
Office
Jun. 30, 2017
USD ($)
Office
Jun. 30, 2016
Office
Dec. 31, 2016
USD ($)
Class of Stock [Line Items]            
Number of offices in the United States and Canada | Office       80    
Formation date       2013-06    
Percentage of common stock distributed       80.00%    
Commission's receivable settled period       10 days    
Marketable securities, available for sale   $ 123,658,000   $ 123,658,000   $ 104,929,000
IPO MMI [Member]            
Class of Stock [Line Items]            
IPO completion date       Oct. 30, 2013    
Accounting Standards Update 2016-13 [Member] | Average AA Credit Rating [Member]            
Class of Stock [Line Items]            
Marketable securities, available for sale   123,700,000   $ 123,700,000    
Impairment write-downs marketable securities, available for sale       0    
Accounting Standards Update 2016-09 [Member]            
Class of Stock [Line Items]            
Cumulative effect adjustments, net of tax $ 52,000          
Accounting Standards Update 2016-02 [Member]            
Class of Stock [Line Items]            
Operating lease obligations   $ 82,800,000   $ 82,800,000    
Geographic Concentration Risk [Member] | Total revenues [Member]            
Class of Stock [Line Items]            
Concentration risk percentage   10.00% 10.00% 10.00% 10.00%  
Number of offices | Office   1 0 0 0  
Customer Concentration Risk [Member] | Total revenues [Member]            
Class of Stock [Line Items]            
Concentration risk percentage   10.00% 10.00% 10.00% 10.00%  
Customer Concentration Risk [Member] | Commissions receivable [Member]            
Class of Stock [Line Items]            
Concentration risk percentage   10.00% 10.00% 10.00% 10.00%  
International Revenues [Member] | Geographic Concentration Risk [Member] | Total revenues [Member] | Maximum [Member]            
Class of Stock [Line Items]            
Concentration risk percentage   1.00% 1.00% 1.00% 1.00%