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Employee Benefit Plans (Details) - USD ($)
$ in Millions
12 Months Ended
Jan. 01, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]        
Employer matching contribution   4.50% 4.00%  
Matching contributions recorded in compensation and related expense   $ 5.7 $ 5.0 $ 4.8
Number of hours of service for vesting, per year   1000 hours    
Number of years of service for vesting   2 years    
Annual vesting percentage   20.00%    
Number of years for incremental percentage vesting until participant fully vested in company's matching contribution   4 years    
Maximum number of shares of Class B common stock for Employee Stock Purchase Plan   750,000    
Employee stock purchase plan, maximum annual contributions per employee, Percent   10.00%    
Number of shares purchased by employees   8,706    
Number of shares purchased by employees since inception   194,224    
Subsequent Event        
Defined Contribution Plan Disclosure [Line Items]        
Employer matching contribution 5.00%      
First Salary Deferral Contribution        
Defined Contribution Plan Disclosure [Line Items]        
Employer matching contribution   100.00% 100.00%  
Percent of employees' gross pay   3.00% 2.00%  
First Salary Deferral Contribution | Subsequent Event        
Defined Contribution Plan Disclosure [Line Items]        
Employer matching contribution 100.00%      
Percent of employees' gross pay 4.00%      
Second Salary Deferral Contribution        
Defined Contribution Plan Disclosure [Line Items]        
Employer matching contribution   50.00% 50.00%  
Percent of employees' gross pay   3.00% 4.00%  
Second Salary Deferral Contribution | Subsequent Event        
Defined Contribution Plan Disclosure [Line Items]        
Employer matching contribution 50.00%      
Percent of employees' gross pay 2.00%      
Minimum        
Defined Contribution Plan Disclosure [Line Items]        
Salary deferral contributions rate   1.00%    
Maximum        
Defined Contribution Plan Disclosure [Line Items]        
Salary deferral contributions rate   50.00%