Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial Assets
Financial assets, fair value	$ 145,821	$ 68,216
Money market funds
Financial Assets
Financial assets, fair value	43,306	7,023
U.S. treasury securities
Financial Assets
Financial assets, fair value	71,464
U.S. government agency securities
Financial Assets
Financial assets, fair value	10,534
Reverse repurchase agreements
Financial Assets
Financial assets, fair value		6,250
Commercial paper
Financial Assets
Financial assets, fair value	1,751	15,193
Corporate bonds
Financial Assets
Financial assets, fair value	18,766	39,750
Level 1
Financial Assets
Financial assets, fair value	43,306	7,023
Level 1 | Money market funds
Financial Assets
Financial assets, fair value	43,306	7,023
Level 2
Financial Assets
Financial assets, fair value	102,515	61,193
Level 2 | U.S. treasury securities
Financial Assets
Financial assets, fair value	71,464
Level 2 | U.S. government agency securities
Financial Assets
Financial assets, fair value	10,534
Level 2 | Reverse repurchase agreements
Financial Assets
Financial assets, fair value		6,250
Level 2 | Commercial paper
Financial Assets
Financial assets, fair value	1,751	15,193
Level 2 | Corporate bonds
Financial Assets
Financial assets, fair value	$ 18,766	$ 39,750