Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accrued Expenses
Research and development expenses	$ 1,238	$ 123
Employee-related expenses	699
Licensing fees		250
Vixen contract payable.	100
Professional fees	98	283
Other	63	89
Total accrued expenses	$ 2,198	$ 745