Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - 2010 Plan, 2018 Plan and ESPP - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,955	$ 141	$ 3,278	$ 280
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,047	109	1,713	214
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 908	$ 32	$ 1,565	$ 66