Fair value measurements - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair value
Less than 12 months	$ 198,601	$ 287,982
12 months or greater	11,377	1,205
Total	209,978	289,187
Unrealized losses
Less than 12 months	(89)	(114)
12 months or greater	(4)	0
Total	(93)	(114)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	124,322	211,384
12 months or greater	0	0
Total	124,322	211,384
Unrealized losses
Less than 12 months	(58)	(74)
12 months or greater	0	0
Total	(58)	(74)
Corporate bonds
Fair value
Less than 12 months	74,279	76,598
12 months or greater	11,377	1,205
Total	85,656	77,803
Unrealized losses
Less than 12 months	(31)	(40)
12 months or greater	(4)	0
Total	$ (35)	$ (40)