Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Expenses
Payroll and related costs	$ 1,483	$ 1,364
Clinical studies and drug development	1,945	2,781
Professional fees	343	204
Short-term lease liabilities	321
Other	139	88
Total accrued expenses	$ 4,231	$ 4,437