Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accrued Expenses
Accrued compensation	$ 1,252	$ 1,181
Accrued contracted research costs	1,850	1,261
Accrued professional fees	215	181
Accrued other	360	655
Total	$ 3,677	$ 3,278