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Common Stock - Additional Information (Detail)
$ / shares in Units, $ in Millions
 12 Months Ended
Apr. 09, 2019
shares
Sep. 11, 2018
$ / shares
shares
Aug. 14, 2018
USD ($)
$ / shares
shares
Aug. 08, 2018
shares
Sep. 30, 2021
USD ($)
$ / shares
shares
Sep. 30, 2020
$ / shares
shares
Apr. 09, 2020
$ / shares
Jun. 28, 2018
shares
Class of Warrant or Right [Line Items]                
Warrants term         5 years      
Warrants of common stock exercise price | $ / shares         $ 0.004   $ 3.98  
Maximum percentage of stock pertaining to restrictions         24.90%      
Extended term of outstanding warrants expiration period         5 years      
Warrants of common stock expiration date         Sep. 30, 2023      
Warrants to purchase shares of common stock               250,000
Common stock, stock split         effected a 2.5-for-1 stock split      
Stock split ratio       2.5        
Common stock, shares authorized       125,000,000 125,000,000 125,000,000    
Preferred stock, shares authorized       5,000,000 5,000,000 5,000,000    
Stock issued during period, shares, new issues   1,344,500            
Common stock, no par value | $ / shares         $ 0 $ 0    
Common stock, warrants issued         4,899,497 0    
Common stock, warrants outstanding         4,899,497 0    
2018 Equity Incentive Plan [Member]                
Class of Warrant or Right [Line Items]                
Increase in number of shares authorized for issuance 1,000,000              
Common stock, shares authorized 3,500,000              
IPO [Member]                
Class of Warrant or Right [Line Items]                
Stock issued during period, shares, new issues     9,630,000          
Common stock, no par value | $ / shares              
Shares issued, price per share | $ / shares     $ 12.00          
Gross proceeds of initial public offering | $     $ 115.6   $ 124.2      
Net proceeds from initial public offering | $         111.7      
Underwriting discounts and commissions | $         8.7      
Offering costs | $         $ 3.6      
Underwriter Options [Member]                
Class of Warrant or Right [Line Items]                
Common stock, warrants issued     1,444,500          
Purchased Directly From Company [Member]                
Class of Warrant or Right [Line Items]                
Stock issued during period, shares, new issues   723,985            
Purchased Directly From Selling Shareholders [Member]                
Class of Warrant or Right [Line Items]                
Stock issued during period, shares, new issues   620,515            
Firm Shares and Option Shares [Member]                
Class of Warrant or Right [Line Items]                
Shares issued, price per share | $ / shares   $ 12.00