Quarterly report pursuant to Section 13 or 15(d)

Fair value measurements (Details)

v3.20.2
Fair value measurements (Details) - USD ($)
$ in Thousands
Sep. 30, 2020
Dec. 31, 2019
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total $ 321,442 $ 39,130
Recurring basis    
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total 321,442  
Recurring basis | Corporate debt securities    
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total 315,437  
Recurring basis | Agency bonds    
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total 6,005  
Recurring basis | Level 1    
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total 315,437  
Recurring basis | Level 1 | Corporate debt securities    
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total 315,437  
Recurring basis | Level 2    
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total 6,005  
Recurring basis | Level 2 | Agency bonds    
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total $ 6,005