Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Expenses
Research and development costs	$ 2,614	$ 2,771
Professional fees	858	327
Payroll related	2,410	1,094
Other	60	18
Accrued expenses	$ 5,942	$ 4,210