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Employee Benefits (Details) - USD ($)
 12 Months Ended
Jan. 01, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Employee Benefits        
Maximum annual contribution per employee (as a percent)   100.00%    
Maximum annual contributions per employee age 50 or less   $ 18,500 $ 18,000  
Maximum annual contributions per employee over the age of 50   24,500 24,000  
Employer contributions   1,400,000 1,000,000 $ 0
Employer matching percentage 50.00%      
The maximum employer matching contribution percent 6.00%      
Defined contribution plan employers matching contribution vesting period 3 years      
Deferred compensation plan        
Deferred compensation plan liability   2,000,000 600,000  
Deferred compensation plan assets   $ 1,900,000 $ 700,000