Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Accrued research and development expenses	$ 2,193	$ 1,903
Accrued employee bonus compensation	413	776
Employee withholdings	25	42
Other accrued expenses	279	428
Total accrued expenses	$ 2,910	$ 3,149