Common Stock - Private Placement of Common Stock (Details) $ / shares in Units, $ in Thousands					12 Months Ended
	Feb. 05, 2019 $ / shares shares	Mar. 27, 2018 $ / shares shares	Dec. 08, 2017 shares	Nov. 14, 2017 USD ($) item $ / shares shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Private Placement of Common Stock
Gross proceeds				$ 18,000		$ 18,000
Fair value of warrant liability				12,335	$ 3,448	11,862
Net proceeds from issuance of stock in private placement				17,250
Additional proceeds from exercise of warrants					$ 18,000
Additional shares issuable on exercise in cash of warrants | shares					2,958,094,000
Number of warrants exercised | shares					200,000
Proceeds from exercise of warrants					$ 1,217
Issuance costs associated with private placement					359	2,172
Common Stock
Private Placement of Common Stock
Remaining proceeds allocated to common stock				$ 5,665
Warrant Liability | Subsequent Events
Private Placement of Common Stock
Exercise price of warrant | $ / shares	$ 1.95
Private Placement
Private Placement of Common Stock
Number of warrants issued per common stock | shares				1
Issuance costs associated with private placement				$ 750
Allocation of issuance cost to warrants (as a percentage)				68.00%
Allocation of issuance cost to common stock (as a percentage)				32.00%
Issuance costs associated with common stock				$ 236		$ 236
Number of days for registration				30 years
Number of days for declaration				60 years
Number of days for review				90 years
Number of purchasers not registered | item				2
Private Placement | HCV IX and Eli Lilly
Private Placement of Common Stock
Number of affiliated directors and executive officers | item				3
Private Placement | Minimum | HCV IX and Eli Lilly
Private Placement of Common Stock
Direct Holding Common Stock Percentage				5.00%
Private Placement | Maximum
Private Placement of Common Stock
Resale shares | shares			3,734,914
Private Placement | Other expense
Private Placement of Common Stock
Issuance costs associated with warrants				$ 514
Private Placement | Common Stock
Private Placement of Common Stock
Issuance of stock (in shares) | shares				2,958,094		2,958,094
Price per common stock (in dollars per share) | $ / shares				$ 6.085
Private Placement | Warrant Liability
Private Placement of Common Stock
Exercise price of warrant | $ / shares				$ 6.085
Exercise expiring period				7 years
Public Offering
Private Placement of Common Stock
Issuance costs associated with common stock					$ 1,304
Public Offering | Subsequent Events
Private Placement of Common Stock
Number of warrants issued per common stock | shares	1
Public Offering | Common Stock
Private Placement of Common Stock
Issuance of stock (in shares) | shares		2,146,667			2,146,667
Price per common stock (in dollars per share) | $ / shares		$ 7.50
Public Offering | Common Stock | Subsequent Events
Private Placement of Common Stock
Issuance of stock (in shares) | shares	7,557,142
Price per common stock (in dollars per share) | $ / shares	$ 1.75
Public Offering | Warrant Liability | Subsequent Events
Private Placement of Common Stock
Exercise price of warrant | $ / shares	$ 1.75