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Termination of Merger with Illumina (Narrative) (Details) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Feb. 09, 2021
Feb. 26, 2021
Mar. 31, 2020
Dec. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Merger Termination [Line Items]            
Continuation Advances from Illumina     $ 34,000,000.0 $ 18,000,000.0 $ 34,000,000 $ 18,000,000
Gain from Continuation Advances from Illumina         34,000,000 $ 18,000,000
Possible Continuation Advances payable         $ 52,000,000.0  
Period in which company must repay continuation advances if change-of-control transaction is entered into with third party         2 years  
Equity or debt financing that must be raised in a single transaction         $ 100,000,000  
Termination fee received         98,000,000.0  
Advisor fees paid         $ 6,000,000.0  
Subsequent Event [Member]            
Merger Termination [Line Items]            
Continuation Advances paid to Illumina   $ 52,000,000.0        
Notes [Member] | Subsequent Event [Member]            
Merger Termination [Line Items]            
Principal amount of notes $ 900,000,000          
Debt instrument, stated interest rate 1.50%          
Maturity date Feb. 15, 2028