Nature of Business, Basis of Presentation and Liquidity - Liquidity (Details) - USD ($)			12 Months Ended
	Feb. 05, 2019	Mar. 27, 2018	Dec. 31, 2018	Dec. 31, 2017
Liquidity and going concern
Accumulated deficit			$ 153,535,000	$ 130,397,000
Net loss			23,138,000	29,727,000
Net cash used in operating activities			$ (26,033,000)	(22,137,000)
Number of Shares Issuable			2,812,610
Proceeds from issuance of common stock in connection with Subscription Agreement				10,000,000
Cash and cash equivalents			$ 16,284,000	25,737,000
Research and development incentive receivable			$ 836,000	$ 1,744,000
Minimum period to fund operating expense			12 months
Public Offering
Liquidity and going concern
Expected research and development tax incentive payments			$ 836,000
Common Stock | Public Offering
Liquidity and going concern
Issuance of stock (in shares)		2,146,667	2,146,667
Price per common stock (in dollars per share)		$ 7.50
Proceeds from issuance of common stock in connection with Subscription Agreement		$ 14,796,000.000
Common Stock | Public Offering | Subsequent Events
Liquidity and going concern
Issuance of stock (in shares)	7,557,142
Number of Shares Issuable	7,557,142
Price per common stock (in dollars per share)	$ 1.75
Proceeds from issuance of common stock in connection with Subscription Agreement	$ 12,081,000
Common Stock | Over-Allotment Option
Liquidity and going concern
Issuance of stock (in shares)	985,714	280,000
Number of Shares Issuable	985,714
Common Stock | Over-Allotment Option | Subsequent Events
Liquidity and going concern
Issuance of stock (in shares)	985,714