Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Expenses
Accrued compensation	$ 436	$ 1,241
Accrued contracted research costs	511	680
Accrued professional fees	346	393
Accrued severance	21	109
Accrued franchise tax	50	168
Accrued other	87	172
Total	$ 1,451	$ 2,763