Summary of Significant Accounting Policies - Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Other Accrued Liabilities
Accrued contract payments	$ 15,576	$ 5,188
Accrued clinical trial costs	11,401	6,418
Accrued professional services	1,200	1,274
Accrued employee benefits	39	314
Accrued public reporting charges	319	180
Other current accrued liabilities	785	558
Total	$ 29,320	$ 13,932