Stockholders’ Equity - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Class of Stock [Line Items]
Total stock-based compensation expense	$ 973	$ 825	$ 3,191	$ 2,261
Employee | Research and development
Class of Stock [Line Items]
Total stock-based compensation expense	462	438	1,687	1,200
Employee | General and administrative
Class of Stock [Line Items]
Total stock-based compensation expense	501	370	1,473	1,001
Non-Employee | Research and development
Class of Stock [Line Items]
Total stock-based compensation expense	8	16	26	56
Non-Employee | General and administrative
Class of Stock [Line Items]
Total stock-based compensation expense	$ 2	$ 1	$ 5	$ 4