Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accrued Expenses
Payroll	$ 385
Legal	909	$ 213
Bonus	300	669
Current portion of deferred rent and lease incentive	312	405
Accrued patent fees	312	219
Accrued R&D costs	1,666	1,649
Other	831	223
Accrued liabilities	$ 4,715	$ 3,378