Quarterly report pursuant to Section 13 or 15(d)

Initial Public Offering - Additional Information (Details)

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Initial Public Offering - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 9 Months Ended
Jun. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Initial Public Offering [Line Items]      
Net proceeds from Initial public offering after underwriting discounts and commissions $ 32,400   $ 32,426
Loss on remeasurement of convertible preferred stock warrant liability     3,725
Reclassification of convertible preferred stock warrant liability into additional paid-in capital $ 5,700   5,711
Common Stock      
Initial Public Offering [Line Items]      
Conversion of preferred stock into common stock, shares 4,689,753 4,689,753  
Additional Paid-in Capital      
Initial Public Offering [Line Items]      
Reclassification of convertible preferred stock warrant liability into additional paid-in capital $ 42,100 $ 42,100  
Offering cost incurred excluding underwriting commissions and discounts $ 1,900    
Nonoperating Income (Expense)      
Initial Public Offering [Line Items]      
Loss on remeasurement of convertible preferred stock warrant liability     $ 3,700
Maximum      
Initial Public Offering [Line Items]      
Number of shares called by warrant 84,000    
IPO      
Initial Public Offering [Line Items]      
Sale of stock, shares 3,220,000    
Price per share $ 11.00    
IPO | Maximum      
Initial Public Offering [Line Items]      
Number of shares called by warrant 84,000