Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Expenses and Other Current Liabilities.
Accrued compensation and benefits	$ 1,077	$ 1,526
Accrued contract manufacturing	2,724	1,003
Accrued clinical costs	459	752
Accrued professional services	678	672
Accrued research costs	201	364
Deferred collaboration reimbursement	430	251
Current portion of operating lease liability	438
Other	344	278
Total accrued expenses and other current liabilities	$ 6,351	$ 4,846