Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial Assets
Financial assets, fair value	$ 103,894	$ 133,775
Corporate bonds
Financial Assets
Financial assets, fair value	17,074	3,001
Commercial paper
Financial Assets
Financial assets, fair value	74,689
Level 1
Financial Assets
Financial assets, fair value	12,131	6,700
Level 2
Financial Assets
Financial assets, fair value	91,763	127,075
Level 2 | Corporate bonds
Financial Assets
Financial assets, fair value	17,074	3,001
Level 2 | Commercial paper
Financial Assets
Financial assets, fair value	74,689
Money market funds
Financial Assets
Financial assets, fair value	12,131	6,700
Money market funds | Level 1
Financial Assets
Financial assets, fair value	$ 12,131	6,700
U.S. government agency securities
Financial Assets
Financial assets, fair value		66,893
U.S. government agency securities | Level 2
Financial Assets
Financial assets, fair value		66,893
U.S. treasury securities
Financial Assets
Financial assets, fair value		57,181
U.S. treasury securities | Level 2
Financial Assets
Financial assets, fair value		$ 57,181