Stockholders’ Equity - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Total stock-based compensation expense	$ 1,232	$ 682	$ 2,218	$ 1,436
Employee | Research and development
Class of Stock [Line Items]
Total stock-based compensation expense	716	422	1,225	762
Employee | General and administrative
Class of Stock [Line Items]
Total stock-based compensation expense	507	248	972	631
Non-Employee | Research and development
Class of Stock [Line Items]
Total stock-based compensation expense	7	11	18	40
Non-Employee | General and administrative
Class of Stock [Line Items]
Total stock-based compensation expense	$ 2	$ 1	$ 3	$ 3