Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring basis - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial assets
Total financial assets	$ 674,408	$ 155,986
Financial liabilities
Total financial liabilities		336
Convertible Preferred Stock Warrant Liability
Financial liabilities
Total financial liabilities		336
Level 1
Financial assets
Total financial assets	88,683	45,998
Level 2
Financial assets
Total financial assets	585,725	109,988
Level 3
Financial liabilities
Total financial liabilities		336
Level 3 | Convertible Preferred Stock Warrant Liability
Financial liabilities
Total financial liabilities		336
Money Market Funds
Financial assets
Total financial assets	88,683	45,998
Money Market Funds | Level 1
Financial assets
Total financial assets	88,683	45,998
Commercial Paper
Financial assets
Total financial assets	121,867	16,887
Commercial Paper | Level 2
Financial assets
Total financial assets	121,867	16,887
U.S. Government Debt and Agency Securities
Financial assets
Total financial assets	377,243	85,623
U.S. Government Debt and Agency Securities | Level 2
Financial assets
Total financial assets	377,243	85,623
Corporate Bonds
Financial assets
Total financial assets	86,615	7,478
Corporate Bonds | Level 2
Financial assets
Total financial assets	$ 86,615	$ 7,478