Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Expenses
Payroll and related costs	$ 1,249	$ 1,962
Clinical and nonclinical trial expenses	3,681	3,958
Professional and consulting fees	446	605
Restructuring expenses	449	1,147
Other	114	212
Total accrued expenses	5,939	7,884
Salary continuation severance benefits	$ 200	$ 700