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Summary of Significant Accounting Policies - Summary of Revenue and Accounts Receivable by Third-party Payors and Other Customers (Details) - Customer Concentration Risk
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Revenue    
Concentration Risk [Line Items]    
Concentration risk, percentage 47.00%  
Revenue | The Big Ten Conference    
Concentration Risk [Line Items]    
Concentration risk, percentage 30.00%  
Revenue | Centura Healthcare    
Concentration Risk [Line Items]    
Concentration risk, percentage 17.00%  
Revenue | Medicare    
Concentration Risk [Line Items]    
Concentration risk, percentage 17.00% 36.00%
Revenue | Covance Central Laboratory Services    
Concentration Risk [Line Items]    
Concentration risk, percentage   21.00%
Accounts Receivable    
Concentration Risk [Line Items]    
Concentration risk, percentage 76.00% 83.00%
Accounts Receivable | The Big Ten Conference    
Concentration Risk [Line Items]    
Concentration risk, percentage 35.00%  
Accounts Receivable | Centura Healthcare    
Concentration Risk [Line Items]    
Concentration risk, percentage 24.00%  
Accounts Receivable | Medicare    
Concentration Risk [Line Items]    
Concentration risk, percentage 6.00% 18.00%
Accounts Receivable | Covance Central Laboratory Services    
Concentration Risk [Line Items]    
Concentration risk, percentage 2.00% 43.00%
Accounts Receivable | Janssen Research and Development, LLC    
Concentration Risk [Line Items]    
Concentration risk, percentage 5.00% 12.00%
Accounts Receivable | Pfizer, Inc    
Concentration Risk [Line Items]    
Concentration risk, percentage 4.00% 10.00%