Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Expenses and Other Current Liabilities.
Accrued compensation and benefits	$ 671	$ 1,526
Accrued contract manufacturing	1,584	1,003
Accrued clinical costs	628	752
Accrued professional services	788	672
Accrued research costs	229	364
Other	996	529
Total accrued expenses and other current liabilities	$ 4,896	$ 4,846