Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value of Financial Instruments
Total assets measured at fair value	$ 585,435	$ 219,158
Money market funds
Fair Value of Financial Instruments
Money market funds	585,435	219,158
Quoted Prices in active Markets for Identical Assets (Level 1)
Fair Value of Financial Instruments
Total assets measured at fair value	585,435	219,158
Quoted Prices in active Markets for Identical Assets (Level 1) | Money market funds
Fair Value of Financial Instruments
Money market funds	585,435	219,158
Significant Observable Inputs (Level 2)
Fair Value of Financial Instruments
Total assets measured at fair value	0	0
Significant Observable Inputs (Level 2) | Money market funds
Fair Value of Financial Instruments
Money market funds	0	0
Significant Unobservable Inputs (Level 3)
Fair Value of Financial Instruments
Total assets measured at fair value	0	0
Significant Unobservable Inputs (Level 3) | Money market funds
Fair Value of Financial Instruments
Money market funds	$ 0	$ 0