Common Stock Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	12 Months Ended
	Nov. 01, 2017	Dec. 02, 2014	Nov. 25, 2014	May 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 30, 2017
Class of Warrant or Right [Line Items]
Warrant liability					$ 0	$ 5
Change in fair value of warrant					(5)	$ (110)	$ (3,104)
Second Tranche | Silicon Valley Bank | Term Loan
Class of Warrant or Right [Line Items]
Amount borrowed				$ 5,000
Exercise of stock warrants (in shares)				27,500
Exercise of stock warrants (in dollars per share)				$ 11.83
2014 SVB Warrant | Common Stock
Class of Warrant or Right [Line Items]
Shares of common stock into which warrants are exercisable (in shares)			27,500
Warrant issued, exercise price (in dollars per share)			$ 11.04
Warrant life			10 years
Warrant liability			$ 300
PIPE Warrants
Class of Warrant or Right [Line Items]
Proceeds from issuance of warrants		$ 3,000
Change in fair value of warrant					$ (5)
PIPE Warrants | Common Stock
Class of Warrant or Right [Line Items]
Shares of common stock into which warrants are exercisable (in shares)		871,840
Warrant issued, exercise price (in dollars per share)		$ 15.00
Warrant life		3 years
November 2017 Warrants | Common Stock
Class of Warrant or Right [Line Items]
Shares of common stock into which warrants are exercisable (in shares)								10,000,000
Warrant issued, exercise price (in dollars per share)								$ 0.80
Warrant life	5 years