Quarterly report pursuant to Section 13 or 15(d)

Redeemable Convertible Preferred Stock - Additional Information (Details)

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Redeemable Convertible Preferred Stock - Additional Information (Details)
$ / shares in Units, $ in Thousands
 1 Months Ended 3 Months Ended 9 Months Ended
Oct. 01, 2018
Aug. 31, 2017
$ / shares
shares
Jul. 31, 2018
USD ($)
$ / shares
shares
Sep. 30, 2018
USD ($)
Director
$ / shares
shares
Sep. 30, 2017
USD ($)
Dec. 31, 2017
$ / shares
shares
Temporary Equity [Line Items]            
Funding through sale of stock | $       $ 84,739 $ 0  
Temporary equity, description       At the election of the holders of a majority of the then-outstanding shares of preferred stock, voting together as a single class on an as-converted to common stock basis, the Company will redeem all outstanding shares of preferred stock in three equal annual installments commencing May 24, 2023, by paying in cash an amount per share equal to the original issuance prices of $0.59 per share of Series A redeemable convertible preferred stock, $0.8822 per share of Series B redeemable convertible preferred stock, $0.4797 per share of Series C redeemable convertible preferred stock, $0.5996 per share of Series C-2 redeemable convertible preferred stock, $0.5996 per share of Series D redeemable convertible preferred stock, $0.6596 per share of Series D-2 redeemable convertible preferred stock, and $0.2674 per share of Series E redeemable convertible preferred stock, plus 8% of the applicable original issuance prices per annum calculated from the original issuance date of each share of preferred stock.    
Preferred stock redemption commencing period       May 24, 2023    
Percentage of issuance price calculated per annum added to original issuance price to determine redemption price       8.00%    
Number of directors common shareholders are entitled to elect | Director       1    
Voting rights per share       one vote per share    
Series E Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Funding through sale of stock | $     $ 85,400      
Sale and issuance of shares | shares     319,305,718      
Redeemable convertible preferred stock, par value     $ 0.2674      
Original issuance price, per share       $ 0.2674    
Dividends declared per share rate       $ 0.0214    
Number of directors preferred shareholders are entitled to elect | Director       1    
Redeemable conversion price per share       $ 0.2674    
Preferred stock, conversion basis 1-for-0.0275          
Exercise price per share       $ 0.2674   $ 0.2674
Series E Redeemable Convertible Preferred Stock | Oxford Finance LLC and Silicon Valley Bank | Loan and Security Agreement            
Temporary Equity [Line Items]            
Issuance of warrants to purchase shares | shares   1,682,871        
Exercise price per share   $ 0.2674        
Term of warrant exercisable   10 years        
Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Sale and issuance of shares | shares       493,615,703   173,750,421
Redeemable convertible preferred stock, par value       $ 0.001   $ 0.001
Temporary Equity liquidation percentage of voting power       Unless the holders of a majority of the then-outstanding shares of preferred stock, voting together as a single class on an as-converted to common stock basis, elect otherwise, any of the following events shall be treated as a liquidation: (i) any consolidation, merger, acquisition, or any other corporate reorganization in which the stockholders of the Company immediately prior to such event own less than 50% of the voting power of the surviving or successor entity or its parent immediately after such event; (ii) any transaction or series of related transactions in which in excess of 50% of the Company’s voting power is transferred; or (iii) any sale, lease, transfer, exclusive license, or other disposition of all or substantially all of the assets of the Company.    
Series A Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Original issuance price, per share       $ 0.5900   0.5900
Dividends declared per share rate       $ 0.0472    
Number of directors preferred shareholders are entitled to elect | Director       1    
Redeemable conversion price per share       $ 0.3756    
Preferred stock, conversion basis 1-for-0.0433          
Series B Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Original issuance price, per share       0.8822   0.8822
Dividends declared per share rate       $ 0.07056    
Number of directors preferred shareholders are entitled to elect | Director       1    
Redeemable conversion price per share       $ 0.4203    
Preferred stock, conversion basis 1-for-0.0578          
Exercise price per share       0.8822   0.8822
Series C Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Original issuance price, per share       0.4797   0.4797
Dividends declared per share rate       $ 0.03838    
Number of directors preferred shareholders are entitled to elect | Director       2    
Redeemable conversion price per share       $ 0.3573    
Preferred stock, conversion basis 1-for-0.0370          
Exercise price per share [1]       0.4797   0.4797
Series C-2 Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Original issuance price, per share       0.5996   0.5996
Dividends declared per share rate       0.048    
Redeemable conversion price per share       0.4081    
Preferred stock, conversion basis 1-for-0.0405          
Series D Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Original issuance price, per share       0.5996   0.5996
Dividends declared per share rate       0.048    
Redeemable conversion price per share       0.4081    
Preferred stock, conversion basis 1-for-0.0405          
Series D-2 Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Original issuance price, per share       0.6596   0.6596
Dividends declared per share rate       0.0528    
Redeemable conversion price per share       0.4336    
Preferred stock, conversion basis 1-for-0.0419          
Exercise price per share       $ 0.6596   $ 0.6596
Series D-2 Redeemable Convertible Preferred Stock | Oxford Finance LLC and Silicon Valley Bank | Loan and Security Agreement            
Temporary Equity [Line Items]            
Issuance of warrants to purchase shares | shares   682,230        
Exercise price per share   $ 0.6596        
[1] On October 1, 2018, 1,232,220 shares of the Series C redeemable convertible preferred warrants will be canceled, and the remaining 687,928 shares will be converted to warrants to purchase common stock on a 1-for-0.0370 basis. All Series E redeemable convertible preferred warrants will be converted to warrants to purchase common stock at a on a 1-for-0.0275 basis.