Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accrued expenses
Accrued employee compensation and benefits	$ 1,264	$ 27
Accrued clinical trial costs	11,183	2,204
Accrued professional fees	490	516
Accrued income taxes	65	99
Other	358	134
Total accrued expenses	$ 13,360	$ 2,980