Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial Assets
Financial assets, fair value	$ 133,881	$ 68,216
Commercial paper
Financial Assets
Financial assets, fair value		15,193
Money market funds
Financial Assets
Financial assets, fair value	48,128	7,023
U.S. treasury securities
Financial Assets
Financial assets, fair value	71,608
U.S. government agency securities
Financial Assets
Financial assets, fair value	6,012
Reverse repurchase agreements
Financial Assets
Financial assets, fair value		6,250
Corporate bonds
Financial Assets
Financial assets, fair value	8,133	39,750
Level 1
Financial Assets
Financial assets, fair value	48,128	7,023
Level 1 | Money market funds
Financial Assets
Financial assets, fair value	48,128	7,023
Level 2
Financial Assets
Financial assets, fair value	85,753	61,193
Level 2 | Commercial paper
Financial Assets
Financial assets, fair value		15,193
Level 2 | U.S. treasury securities
Financial Assets
Financial assets, fair value	71,608
Level 2 | U.S. government agency securities
Financial Assets
Financial assets, fair value	6,012
Level 2 | Reverse repurchase agreements
Financial Assets
Financial assets, fair value		6,250
Level 2 | Corporate bonds
Financial Assets
Financial assets, fair value	$ 8,133	$ 39,750