Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accrued expenses
Accrued employee compensation and benefits	$ 311	$ 27
Accrued clinical trial costs	4,639	2,204
Accrued professional fees	1,689	516
Accrued income taxes	292	99
Other		134
Total accrued expenses	$ 6,931	$ 2,980