Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring basis - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets
Total financial assets	$ 623,504	$ 786,641
Level 1
Financial assets
Total financial assets	113,486	103,283
Level 2
Financial assets
Total financial assets	510,018	683,358
Money Market Funds
Financial assets
Total financial assets	113,486	103,283
Money Market Funds | Level 1
Financial assets
Total financial assets	113,486	103,283
U.S. Government Debt Securities
Financial assets
Total financial assets	482,044	671,777
U.S. Government Debt Securities | Level 2
Financial assets
Total financial assets	482,044	671,777
Corporate Bonds
Financial assets
Total financial assets	27,974	11,581
Corporate Bonds | Level 2
Financial assets
Total financial assets	$ 27,974	$ 11,581