Share-Based Compensation - Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 270	$ 295	$ 867	$ 861
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	24	56	120	181
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 246	$ 239	$ 747	$ 680