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Fair value of financial instruments and marketable securities - Marketable securities (Details) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Marketable securities on the balance sheet    
Total Marketable securities, Less Than 12 Months $ 450,923 $ 588,863
Total Marketable securities, More Than 12 Months 191,154 305,975
Commercial paper    
Marketable securities on the balance sheet    
Total Marketable securities, Less Than 12 Months 252,802 276,837
Corporate debt securities    
Marketable securities on the balance sheet    
Total Marketable securities, Less Than 12 Months 164,640 240,139
Total Marketable securities, More Than 12 Months 166,593 235,520
Asset-backed securities    
Marketable securities on the balance sheet    
Total Marketable securities, Less Than 12 Months 5,321 6,363
Total Marketable securities, More Than 12 Months 13,999 22,525
Government obligations    
Marketable securities on the balance sheet    
Total Marketable securities, Less Than 12 Months 28,160 65,524
Total Marketable securities, More Than 12 Months $ 10,562 $ 47,930