Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial Assets
Financial assets, fair value	$ 133,775	$ 68,216
Commercial paper
Financial Assets
Financial assets, fair value		15,193
Corporate bonds
Financial Assets
Financial assets, fair value	3,001	39,750
Money market funds
Financial Assets
Financial assets, fair value	6,700	7,023
U.S. treasury securities
Financial Assets
Financial assets, fair value	57,181
U.S. government agency securities
Financial Assets
Financial assets, fair value	66,893
Reverse repurchase agreements
Financial Assets
Financial assets, fair value		6,250
Level 1
Financial Assets
Financial assets, fair value	6,700	7,023
Level 1 | Money market funds
Financial Assets
Financial assets, fair value	6,700	7,023
Level 2
Financial Assets
Financial assets, fair value	127,075	61,193
Level 2 | Commercial paper
Financial Assets
Financial assets, fair value		15,193
Level 2 | Corporate bonds
Financial Assets
Financial assets, fair value	3,001	39,750
Level 2 | U.S. treasury securities
Financial Assets
Financial assets, fair value	57,181
Level 2 | U.S. government agency securities
Financial Assets
Financial assets, fair value	$ 66,893
Level 2 | Reverse repurchase agreements
Financial Assets
Financial assets, fair value		$ 6,250