Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Payroll and employee related expenses	$ 2,112	$ 2,235
Collaboration and licensing	1,350	1,050
Accrued patent fees	492	487
Accrued external research and development costs	4,247	4,379
Accrued professional and consulting services	763	468
Accrued interest	44	82
Issuance costs, December 2019 financing	0	4,381
Other	300	410
Accrued expenses	$ 9,308	$ 13,492