Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Expenses
Payroll and related costs	$ 1,243	$ 1,364
Clinical studies and drug development	2,771	2,781
Professional fees	356	204
Other	375	88
Total accrued expenses	$ 4,745	$ 4,437