Annual report pursuant to Section 13 and 15(d)

Equity (Detail)

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Equity (Detail)
$ / shares in Units, $ in Thousands
 1 Months Ended 12 Months Ended
May 24, 2019
USD ($)
May 24, 2018
$ / shares
shares
May 08, 2018
$ / shares
shares
Apr. 23, 2018
shares
Sep. 30, 2019
USD ($)
$ / shares
shares
Jun. 30, 2018
$ / shares
Sep. 30, 2019
USD ($)
$ / shares
shares
Sep. 30, 2018
$ / shares
shares
Schedule Of Stockholders Equity [Line Items]                
Common stock, shares outstanding (in shares)     11,250,000         39,464,619
Common stock, shares issued (in shares)               42,387,571
Compensation expense | $             $ 400  
Class B Common Stock                
Schedule Of Stockholders Equity [Line Items]                
Common stock split conversion ratio       25.2        
Conversion of stock, shares issued (in shares)     2,250,000 41,817,537       126,000
Common stock, shares outstanding (in shares)         19,184,009   19,184,009  
Shares issued, price per share (in dollars per share) | $ / shares               $ 0.04
Initial public offering (in shares)             20,355,202 2,600,000
Common stock, shares issued (in shares)         22,106,961   22,106,961  
Exercises in period, weighted average (in dollars per share) | $ / shares           $ 5.70    
Treasury shares issued (in dollars per share) | $ / shares           3.64    
Class A Common Stock                
Schedule Of Stockholders Equity [Line Items]                
Conversion of stock, shares issued (in shares)     2,250,000          
Common stock, shares outstanding (in shares)     9,000,000   32,597,736   32,597,736 11,950,000
Shares issued, price per share (in dollars per share) | $ / shares         $ 14.25   $ 14.25  
Common stock shares sold (in shares)   350,000            
Initial public offering (in shares)             20,355,202 2,600,000
Conversion rate             1  
Common stock, shares issued (in shares)         32,597,736   32,597,736 11,950,000
Exercises in period, weighted average (in dollars per share) | $ / shares           $ 0.0357    
Issuance of stock (in shares)             292,534 9,350,000
Compensation expense | $         $ 700      
2010 non-plan stock option agreement options | Class B Common Stock                
Schedule Of Stockholders Equity [Line Items]                
Conversion of stock, shares issued (in shares)               768,984
Exercises in period, weighted average (in dollars per share) | $ / shares               $ 5.70
Treasury shares issued (in dollars per share) | $ / shares             $ 3.64  
IPO | Class A Common Stock                
Schedule Of Stockholders Equity [Line Items]                
Shares issued, price per share (in dollars per share) | $ / shares   $ 12.00 $ 12.00          
Common stock shares sold (in shares)   700,000            
Over-Allotment Option | Class A Common Stock                
Schedule Of Stockholders Equity [Line Items]                
Issuance of stock (in shares)         5,000,000      
Director                
Schedule Of Stockholders Equity [Line Items]                
Amount of limit of dollar value of equity-based awards | $ $ 750              
Treasury Stock | Class B Common Stock                
Schedule Of Stockholders Equity [Line Items]                
Conversion of stock, shares issued (in shares)       3,170,034        
2018 Equity Incentive Plan | Class B Common Stock                
Schedule Of Stockholders Equity [Line Items]                
Conversion of stock, shares issued (in shares)             74,592  
Shares issued, price per share (in dollars per share) | $ / shares               $ 0.0357
2018 Equity Incentive Plan | Class A Common Stock                
Schedule Of Stockholders Equity [Line Items]                
Conversion of stock, shares issued (in shares)             292,534