Related Party Transactions (Details)		3 Months Ended
	Nov. 14, 2017 director $ / shares shares	Mar. 31, 2018 shares
Private placement
Related Party Transactions
Number of warrants issued per common stock	1
Private placement | HCV IX and Eli Lilly
Related Party Transactions
Number of affiliated directors and executive officers | director	3
Private placement | HCV IX and Eli Lilly | Minimum
Related Party Transactions
Direct holding percentage	5.00%
Common Stock
Related Party Transactions
Issuance of stock (in shares)		2,146,667
Common Stock | Private placement
Related Party Transactions
Issuance of stock (in shares)	2,958,094
Price per share (in dollars per share) | $ / shares	$ 6.085
Warrant Liability | Private placement
Related Party Transactions
Exercise price of warrant | $ / shares	$ 6.085