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Common Stock - Additional Information (Detail)
$ / shares in Units, $ in Millions
 12 Months Ended
Sep. 11, 2018
$ / shares
shares
Aug. 14, 2018
USD ($)
$ / shares
shares
Aug. 08, 2018
shares
Sep. 30, 2018
USD ($)
$ / shares
shares
Jun. 28, 2018
shares
Sep. 30, 2017
$ / shares
shares
Class of Warrant or Right [Line Items]            
Warrants term       5 years    
Warrants of common stock exercise price | $ / shares       $ 0.004    
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       10,614,990   12,230,625
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 | $       $ 3.8    
Underwriter Options [Member]            
Class of Warrant or Right [Line Items]            
Common stock, warrants issued   1,444,500        
Firm Shares and Option Shares [Member]            
Class of Warrant or Right [Line Items]            
Shares issued, price per share | $ / shares $ 12.00          
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