Annual report pursuant to Section 13 and 15(d)

Convertible Preferred Stock Warrants and Common Stock Warrants - Schedule of Warrants Issued and Outstanding (Details)

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Convertible Preferred Stock Warrants and Common Stock Warrants - Schedule of Warrants Issued and Outstanding (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Jun. 30, 2017
Dec. 31, 2016
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding 163,713 468,278   680,027
Fair value of warrants issued and outstanding     $ 300 $ 1,875
The June 2012 Series B-1 convertible preferred stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding       25,568
Fair value of warrants issued and outstanding       $ 303
Issuance Date 2012-06      
Price per Share $ 5.8667      
Expiration Date 2022-06      
The July 2012 Series B-1 convertible preferred stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding       167,428
Fair value of warrants issued and outstanding       $ 263
Issuance Date 2012-07      
Price per Share $ 5.8667      
Expiration Date 2019-07      
The August 2012 Series B-1 convertible preferred stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding       145,801
Fair value of warrants issued and outstanding       $ 46
Issuance Date 2012-08      
Price per Share $ 5.8667      
Expiration Date 2019-08      
The November 2012 Series B-1 convertible preferred stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding       10,517
Fair value of warrants issued and outstanding       $ 19
Issuance Date 2012-11      
Price per Share $ 5.8667      
Expiration Date 2022-11      
The February 2014 Series B-1 convertible preferred stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding       156,851
Fair value of warrants issued and outstanding       $ 929
Issuance Date 2014-02      
Price per Share $ 0.1700      
Expiration Date 2021-02      
The September 2015 Series B-1 convertible preferred stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding       173,862
Fair value of warrants issued and outstanding       $ 315
Issuance Date 2015-09      
Price per Share $ 5.8667      
Expiration Date 2025-09      
The July 2012 Common stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding 3,766 165,925    
Issuance Date 2012-07      
Price per Share $ 5.8667      
Expiration Date 2019-07      
The August 2012 Common stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding 25,231 61,502    
Issuance Date 2012-08      
Price per Share $ 5.8667      
Expiration Date 2019-08      
The February 2014 Common stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding 50,716 156,851    
Issuance Date 2014-02      
Price per Share $ 0.1700      
Expiration Date 2021-02      
The June 2017 Common stock warrant        
Class Of Warrant Or Right [Line Items]        
Shares of warrants issued and outstanding [1] 84,000 84,000    
Issuance Date [1] 2017-06      
Price per Share [1] $ 13.2000      
Expiration Date [1] 2020-06      
[1] This warrant was issued to the Company’s lead underwriter in connection with the IPO.