Annual report pursuant to Section 13 and 15(d)

Initial Public Offering - Additional Information (Details)

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Initial Public Offering - Additional Information (Details) - USD ($)
 1 Months Ended 12 Months Ended
Jun. 30, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Initial Public Offering [Line Items]        
Net proceeds from Initial public offering excluding underwriting discounts and commissions $ 32,400,000   $ 32,426,000  
Loss on remeasurement of convertible preferred stock warrant liability     3,725,000 $ 524,000
Reclassification of convertible preferred stock warrant liability into additional paid-in capital $ 5,700,000   5,711,000  
Offering cost incurred excluding underwriting commissions and discounts     $ 1,870,000  
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 $ 42,100,000   $ 42,100,000  
Offering cost incurred excluding underwriting commissions and discounts $ 1,900,000   $ 1,870,000  
Maximum        
Initial Public Offering [Line Items]        
Number of shares called by warrant 84,000      
Minimum        
Initial Public Offering [Line Items]        
Net proceeds from Initial public offering excluding underwriting discounts and commissions $ 25,000,000      
Other Expense, Net        
Initial Public Offering [Line Items]        
Loss on remeasurement of convertible preferred stock warrant liability   $ 3,700,000    
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