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401(k) Plan (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Retirement Benefits [Abstract]      
Company matching cash contributions 50.00%    
Maximum annual contributions per employee $ 5,000    
Expense for matching contributions $ 1,700,000 $ 1,200,000 $ 900,000