Stockholders’ Equity - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Class of Stock [Line Items]
Total stock-based compensation expense	$ 986	$ 754
Employee | Research and development
Class of Stock [Line Items]
Total stock-based compensation expense	509	340
Employee | General and administrative
Class of Stock [Line Items]
Total stock-based compensation expense	465	383
Non-Employee | Research and development
Class of Stock [Line Items]
Total stock-based compensation expense	11	29
Non-Employee | General and administrative
Class of Stock [Line Items]
Total stock-based compensation expense	$ 1	$ 2