Nature of Business, Basis of Presentation and Liquidity - Liquidity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Liquidity
Accumulated deficit	$ 130,397	$ 100,670
Net loss	29,727	25,632
Net cash used in operating activities	(22,137)	(25,337)
Cash and cash equivalents	25,737	793
Research and development incentive receivable	$ 1,744	$ 3,053
Minimum period to fund Operating expense	12 months