Related Party Transaction (Details) - USD ($)			1 Months Ended	12 Months Ended
	Apr. 26, 2016	Mar. 29, 2016	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Public Offerings
Proceeds from sale of stock				$ 64,877,000	$ 711,000
Director
Related Party Transaction
Purchase of research services					$ 461,000
IPO
Public Offerings
Share offering price		$ 15.00
Exchange warrants		4,700,000
Net proceeds from IPO	$ 70,600,000
Over-Allotment Option
Public Offerings
Share offering price	$ 15.00
Exchange warrants	502,618		1,058,823
Follow On Public Offering
Public Offerings
Share offering price			$ 8.50
Exchange warrants			8,117,647
Proceeds from sale of stock			$ 64,900,000
Follow On Public Offering | FMR LLC
Public Offerings
Exchange warrants			1,176,470
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 9,999,995
Follow On Public Offering | Orbimed Advisors LLC
Public Offerings
Exchange warrants			588,235
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 4,999,998
Follow On Public Offering | Novo Holdings A/S
Public Offerings
Exchange warrants			1,176,470
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 9,999,995
Follow On Public Offering | Adams Street Partners
Public Offerings
Exchange warrants			588,235
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 4,999,998
Follow On Public Offering | Director
Public Offerings
Exchange warrants			100,000
Owners of More Than 5% of Our Common Stock or Board of Directors
Aggregate Purchase Price			$ 850,000