The Company and a Summary of its Significant Accounting Policies - Summary of Percentages of Total Revenue or Accounts Receivable for Third Party Payers and Pharmaceutical Customers (Parenthetical) (Details) - Customer Concentration Risk
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Total Revenue | Assay Revenue Payor A      
Product Information [Line Items]      
Concentration risk, percentage 36.00% 32.00%  
Total Revenue | Assay Revenue Payor B      
Product Information [Line Items]      
Concentration risk, percentage   11.00% 12.00%
Total Revenue | Contract Revenue Customer A      
Product Information [Line Items]      
Concentration risk, percentage   23.00% 22.00%
Total Revenue | Contract Revenue Customer C      
Product Information [Line Items]      
Concentration risk, percentage     29.00%
Accounts Receivable | Assay Revenue Payor A      
Product Information [Line Items]      
Concentration risk, percentage 23.00% 21.00%  
Accounts Receivable | Assay Revenue Payor B      
Product Information [Line Items]      
Concentration risk, percentage 15.00%    
Accounts Receivable | Contract Revenue Customer B      
Product Information [Line Items]      
Concentration risk, percentage   17.00%  
Maximum | Total Revenue | Assay Revenue Payor A      
Product Information [Line Items]      
Concentration risk, percentage     10.00%
Maximum | Total Revenue | Assay Revenue Payor B      
Product Information [Line Items]      
Concentration risk, percentage 10.00%    
Maximum | Total Revenue | Contract Revenue Customer A      
Product Information [Line Items]      
Concentration risk, percentage 10.00%    
Maximum | Total Revenue | Contract Revenue Customer B      
Product Information [Line Items]      
Concentration risk, percentage 10.00% 10.00% 10.00%
Maximum | Total Revenue | Contract Revenue Customer C      
Product Information [Line Items]      
Concentration risk, percentage 10.00% 10.00%  
Maximum | Accounts Receivable | Assay Revenue Payor B      
Product Information [Line Items]      
Concentration risk, percentage   10.00%  
Maximum | Accounts Receivable | Contract Revenue Customer A      
Product Information [Line Items]      
Concentration risk, percentage 10.00% 10.00%  
Maximum | Accounts Receivable | Contract Revenue Customer B      
Product Information [Line Items]      
Concentration risk, percentage 10.00%    
Maximum | Accounts Receivable | Contract Revenue Customer C      
Product Information [Line Items]      
Concentration risk, percentage 10.00% 10.00%