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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Award vesting terms Vesting terms ranging from three to five years and include 1) options that vest in one-fifth increments beginning on the grant date and continuing on each of the first four anniversaries of the grant date and 2) options that cliff-vest on the fifth anniversary of the grant date.  
Common Class A [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Options granted 86,000  
Minimum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Award vesting period 3 years  
Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Award vesting period 5 years  
1996 Equity Incentive Plan [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Shares reserved for issuance to directors and employees 15,500,000  
Number of shares available for grant under Incentive Plan 1,466,193  
Compensation expense related to performance based compensation agreements $ 11,800  
1996 Equity Incentive Plan [Member] | Minimum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Range of awards of target number of share 0.00%  
1996 Equity Incentive Plan [Member] | Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Range of awards of target number of share 100.00%  
Restricted Stock [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expiration date of options granted under equity incentive plan 10 years  
Restricted Stock [Member] | 1996 Equity Incentive Plan [Member] | Percentage of awards vesting on grant date [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Percentage of awards vesting on grant date 50.00%  
Restricted Stock [Member] | 1996 Equity Incentive Plan [Member] | Percentage of Awards Vesting On Last Day of Each Directors Term [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Percentage of awards vesting on grant date 50.00%  
Restricted Stock [Member] | 1996 Equity Incentive Plan [Member] | Common Class A [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Compensation expense related to performance based compensation agreements $ 301  
2009 Employee Stock Purchase Plan [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Number of shares available for grant under Incentive Plan 276,694 279,589
Additional shares reserved under 2009 ESPP 82,084  
2009 Employee Stock Purchase Plan [Member] | Common Class A [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Additional shares reserved under 2009 ESPP 82,084