Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accrued Expenses
Accrued compensation	$ 752	$ 796
Accrued contracted research costs	1,164	1,109
Accrued professional fees	369	791
Accrued other	278	97
Total	$ 2,563	$ 2,793