Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued expenses
Accrued payroll and related expenses	$ 3,080	$ 3,042
Accrued preclinical, manufacturing and clinical expenses	4,017	8,314
Accrued professional fees	710	567
Accrued other	230	452
Total	$ 8,037	$ 12,375