Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Payroll and employee related expenses	$ 1,401	$ 2,235
Collaboration and licensing	0	1,050
Accrued patent fees	1,324	487
Accrued external research and development costs	5,414	4,379
Accrued professional and consulting services	353	446
Accrued interest	60	82
Issuance costs, December 2019 financing	0	4,381
Other	223	432
Accrued expenses	$ 8,775	$ 13,492