Convertible Preferred Stock and Common Stock - Additional Information (Details)
 1 Months Ended 3 Months Ended
Apr. 20, 2018
Apr. 30, 2018
USD ($)
$ / shares
shares
Mar. 31, 2018
USD ($)
$ / shares
shares
Mar. 31, 2018
USD ($)
$ / shares
shares
Mar. 31, 2017
USD ($)
May 07, 2018
$ / shares
shares
Feb. 28, 2018
shares
Dec. 31, 2017
shares
Class Of Stock [Line Items]                
Common stock, shares authorized     140,000,000 140,000,000     122,000,000 122,000,000
Preferred stock, shares authorized     103,283,818 103,283,818     91,739,149  
Number of stock, shares issued     31,750,297 31,750,297       28,159,724
Net proceeds from sale of convertible preferred stock | $       $ 54,951,000 $ 7,984,000      
Subsequent Event                
Class Of Stock [Line Items]                
Conversion ratio of preferred stock 0.33898              
Subsequent Event | IPO                
Class Of Stock [Line Items]                
Common stock, shares authorized           300,000,000    
Preferred stock, shares authorized           10,000,000    
Number of preferred stock issued upon conversion           32,073,149    
Share price | $ / shares           $ 17.00    
Common Stock                
Class Of Stock [Line Items]                
Conversion ratio of preferred stock       1        
Common Stock | IPO                
Class Of Stock [Line Items]                
Share price | $ / shares     $ 15.3317 $ 15.3317        
Percentage of preferred stock outstanding       60.00%        
Common Stock | Minimum | IPO                
Class Of Stock [Line Items]                
Gross proceeds from public offering | $       $ 30,000,000        
Series C Convertible Preferred Stock                
Class Of Stock [Line Items]                
Preferred stock, shares authorized     11,544,669 11,544,669        
Number of stock, shares issued     3,590,573 3,590,573        
Shares price per share | $ / shares     $ 15.3317 $ 15.3317        
Net proceeds from sale of convertible preferred stock | $     $ 54,900,000          
Liquidation preference per share | $ / shares     $ 15.3317 $ 15.3317        
Series C Convertible Preferred Stock | Subsequent Event                
Class Of Stock [Line Items]                
Number of stock, shares issued   322,852            
Shares price per share | $ / shares   $ 15.3317            
Net proceeds from sale of convertible preferred stock | $   $ 5,000,000            
Series C Convertible Preferred Stock | U.S. National Securities Exchange | Minimum                
Class Of Stock [Line Items]                
Gross proceeds from public offering | $     $ 30,000,000          
Series C Convertible Preferred Stock | Common Stock                
Class Of Stock [Line Items]                
Number of preferred stock issued upon conversion     1 1        
Conversion price of preferred stock | $ / shares     $ 15.3317 $ 15.3317        
Series A-1 Convertible Preferred Stock                
Class Of Stock [Line Items]                
Number of stock, shares issued     2,887,086 2,887,086       2,887,086
Conversion price of preferred stock | $ / shares     $ 0.864 $ 0.864        
Liquidation preference per share | $ / shares     $ 0.864 $ 0.864        
Series A-2 Convertible Preferred Stock                
Class Of Stock [Line Items]                
Number of stock, shares issued     10,498,269 10,498,269       10,498,269
Conversion price of preferred stock | $ / shares     $ 0.876 $ 0.876        
Liquidation preference per share | $ / shares     $ 0.876 $ 0.876        
Series B Convertible Preferred Stock                
Class Of Stock [Line Items]                
Number of stock, shares issued     14,774,369 14,774,369       14,774,369
Conversion price of preferred stock | $ / shares     $ 12.125 $ 12.125        
Liquidation preference per share | $ / shares     $ 12.125 $ 12.125        
Noncumulative Preferred Stock                
Class Of Stock [Line Items]                
Dividends rate of respective series of convertible preferred stock issuance price       6.00%