Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Expenses
Accrued compensation	$ 1,241	$ 632
Accrued contracted research costs	680	1,357
Accrued professional fees	393	298
Accrued severance	109
Accrued franchise fee	168
Accrued other	172	145
Total	$ 2,763	$ 2,432