Quarterly report pursuant to Section 13 or 15(d)

Loan and Security Agreement - Additional Information (Details)

v3.10.0.1
Loan and Security Agreement - Additional Information (Details)
1 Months Ended 3 Months Ended 9 Months Ended
Aug. 31, 2017
USD ($)
Installment
$ / shares
shares
Sep. 30, 2018
USD ($)
$ / shares
Jul. 31, 2018
USD ($)
$ / shares
shares
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
$ / shares
Sep. 30, 2017
USD ($)
Aug. 31, 2018
USD ($)
Dec. 31, 2017
$ / shares
Debt Instrument [Line Items]                
Debt, non-current   $ 11,500,000     $ 11,500,000      
Funding through sale of stock         $ 84,739,000 $ 0    
2017 Warrant                
Debt Instrument [Line Items]                
Estimated fair value portion of preferred stock     $ 329,000          
Series D-2 Redeemable Convertible Preferred Stock                
Debt Instrument [Line Items]                
Exercise price per share of warrants | $ / shares   $ 0.6596     $ 0.6596     $ 0.6596
Series D-2 Redeemable Convertible Preferred Stock | 2017 Warrant                
Debt Instrument [Line Items]                
Exercise price per share of warrants | $ / shares $ 0.6596              
Series E Redeemable Convertible Preferred Stock                
Debt Instrument [Line Items]                
Exercise price per share of warrants | $ / shares   $ 0.2674     $ 0.2674     $ 0.2674
Funding through sale of stock     $ 85,400,000          
Sale and issuance of shares | shares     319,305,718          
Redeemable convertible preferred stock, par value | $ / shares     $ 0.2674          
Series E Redeemable Convertible Preferred Stock | 2017 Warrant                
Debt Instrument [Line Items]                
Warrant to purchase stock | shares     1,682,871          
Exercise price per share of warrants | $ / shares     $ 0.2674          
Funding through sale of stock     $ 85,400,000          
Sale and issuance of shares | shares     319,305,718          
Redeemable convertible preferred stock, par value | $ / shares     $ 0.2674          
Warrants exercisable, term     10 years          
August 2017 Loan                
Debt Instrument [Line Items]                
Debt, current   $ 3,200,000     $ 3,200,000      
Debt, non-current   11,500,000     11,500,000      
Interest payable $ 574,500 200,000     $ 200,000      
Average interest rate         8.28%      
Final payment fee percentage 3.83%              
Loan and accretion of debt discount   $ 400,000   $ 200,000 $ 1,200,000 $ 200,000    
August 2017 Loan | Floating Rate                
Debt Instrument [Line Items]                
Interest charges on loan 7.39%              
August 2017 Loan | LIBOR                
Debt Instrument [Line Items]                
Interest charges on loan 6.40%              
Description of interest charges on loan         the sum of the 30-day U.S. Dollar London Interbank Offered Rate (“LIBOR”) plus 6.40%.      
Oxford | Series D-2 Redeemable Convertible Preferred Stock | 2017 Warrant                
Debt Instrument [Line Items]                
Warrant to purchase stock | shares 454,820              
SVB | Series D-2 Redeemable Convertible Preferred Stock | 2017 Warrant                
Debt Instrument [Line Items]                
Warrant to purchase stock | shares 227,410              
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | August 2017 Loan                
Debt Instrument [Line Items]                
Borrowed amount $ 15,000,000           $ 15,000,000  
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | August 2017 Loan | March 2019                
Debt Instrument [Line Items]                
Number of monthly installments | Installment 30              
Payment terms, description         The loan is due in 30 monthly installments from March 2019 through its repayment in August 2021, with interest-only monthly payments until March 2019. If certain qualified funding events occur, the loan will be due in 24 monthly installments from September 2019 through its repayment in August 2021, with interest-only payments until September 2019.      
Repayment installment, start date, month and year 2019-03              
Repayment installment, end date, month and year 2021-08              
Frequency of interest-only payments         monthly payments      
Interest-only payments, maturity month and year 2019-03              
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | August 2017 Loan | September 2019                
Debt Instrument [Line Items]                
Number of monthly installments | Installment 24              
Repayment installment, start date, month and year 2019-09              
Repayment installment, end date, month and year 2021-08              
Interest-only payments, maturity month and year 2019-09