Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Development costs	$ 2,650	$ 2,581
Employee compensation (including reduction in workforce)	896	735
Professional fees	237	463
Other	70	34
Total accrued expenses	$ 3,853	$ 3,813