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Termination of Merger with Illumina (Narrative) (Details) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Jan. 02, 2020
Feb. 28, 2021
Apr. 30, 2020
Mar. 31, 2021
Dec. 31, 2020
Mar. 31, 2020
Dec. 31, 2019
Dec. 31, 2019
Feb. 16, 2021
Merger Termination [Line Items]                  
Continuation Advances           $ 34,000,000.0 $ 18,000,000.0    
Gain (loss) from Continuation Advances       $ (52,000,000)   34,000,000   $ 18,000,000.0  
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      
Continuation Advances paid   $ 52,000,000.0              
Termination fee received $ 98,000,000.0                
Advisor fees paid     $ 6,000,000.0            
Other income, net       $ 64,000 $ 98,000,000.0 $ 238,000      
Convertible Senior Notes [Member]                  
Merger Termination [Line Items]                  
Principal amount of notes   $ 900,000,000              
Debt instrument, stated interest rate   1.50%             1.50%
Maturity date       Feb. 15, 2028