Fair value of financial instruments and investments - Available-for-sale securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Securities in an unrealized loss position less than 12 months	$ (75)	$ (28)
Fair Value	260,970	95,990
Securities in an unrealized loss position greater than 12 months	0	0
Fair Value	0	0
Total	(75)	(28)
Fair Value	260,970	95,990
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Securities in an unrealized loss position less than 12 months	(37)
Fair Value	129,630
Securities in an unrealized loss position greater than 12 months	0
Fair Value	0
Total	(37)
Fair Value	129,630
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Securities in an unrealized loss position less than 12 months	(29)	(20)
Fair Value	102,426	71,779
Securities in an unrealized loss position greater than 12 months	0	0
Fair Value	0	0
Total	(29)	(20)
Fair Value	102,426	71,779
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities in an unrealized loss position less than 12 months	(3)	(8)
Fair Value	1,830	24,211
Securities in an unrealized loss position greater than 12 months	0	0
Fair Value	0	0
Total	(3)	(8)
Fair Value	1,830	$ 24,211
Government obligations
Debt Securities, Available-for-sale [Line Items]
Securities in an unrealized loss position less than 12 months	(6)
Fair Value	27,084
Securities in an unrealized loss position greater than 12 months	0
Fair Value	0
Total	(6)
Fair Value	$ 27,084

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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