Summary of Significant Accounting Policies (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Feb. 28, 2017 USD ($)
Summary of Significant Accounting Policies
PDUFA fee paid, later refunded			$ 2,000
Revenue Recognition
Revenue, Remaining Performance Obligation, Optional Exemption, Performance Obligation [true false]	true
Number of active research grants | item	2
Finished goods inventory	$ 1,026	$ 0