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Fair value of financial instruments and investments - Marketable Securities, Unrealized Gains (Losses) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost $ 377,287 $ 892,938
Gross Unrealized, Gain 107 1,975
Gross Unrealized, Loss (709) (75)
Fair Value 376,685 894,838
Write downs of available for sale debt securities 0 0
Increase in allowance for credit losses 0 0
Realized gain (loss) from sale of marketable securities 800 700
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 75,275 276,855
Gross Unrealized, Gain 5 19
Gross Unrealized, Loss (1) (37)
Fair Value 75,279 276,837
Corporate debt securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 268,246 474,030
Gross Unrealized, Gain 81 1,658
Gross Unrealized, Loss (644) (29)
Fair Value 267,683 475,659
Asset-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 15,287 28,681
Gross Unrealized, Gain 16 210
Gross Unrealized, Loss (5) (3)
Fair Value 15,298 28,888
Government obligations    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 18,479 113,372
Gross Unrealized, Gain 5 88
Gross Unrealized, Loss (59) (6)
Fair Value $ 18,425 $ 113,454