Annual report pursuant to Section 13 and 15(d)

Initial Public Offering (Detail)

v3.10.0.1
Initial Public Offering (Detail)
$ / shares in Units, $ in Millions
May 24, 2018
USD ($)
$ / shares
shares
May 08, 2018
USD ($)
$ / shares
shares
Apr. 23, 2018
$ / shares
shares
Sep. 30, 2018
USD ($)
$ / shares
shares
Sep. 30, 2017
USD ($)
$ / shares
shares
Class of Stock [Line Items]          
Common stock, par value (in dollars per share) | $ / shares     $ 0.001 $ 0.001 $ 0.001
Common stock shares authorized (in shares)       0 126,000,000
Capitalized equity issuance costs | $         $ 2.2
Common stock shares issued (in shares)       0 44,987,575
Common stock, shares outstanding (in shares)       0 41,691,541
Class B Common Stock          
Class of Stock [Line Items]          
Common stock, par value (in dollars per share) | $ / shares       $ 0.001 $ 0.001
Common stock split conversion ratio     25.2    
Conversion of stock, shares issued (in shares)     41,817,537    
Common stock shares authorized (in shares)     100,000,000 100,000,000 0
Common stock shares sold (in shares) 350,000 2,250,000      
Common stock shares issued (in shares) 42,387,571 42,737,571   42,387,571 0
Common stock, shares outstanding (in shares) 39,217,537 39,567,537   39,464,619 0
Class A Common Stock          
Class of Stock [Line Items]          
Common stock, par value (in dollars per share) | $ / shares       $ 0.001 $ 0.001
Conversion of stock, shares issued (in shares) 350,000 2,250,000      
Common stock shares authorized (in shares)     400,000,000 400,000,000 0
Common stock shares sold (in shares) 350,000 9,000,000      
Proceeds from issuance initial public offering | $ $ 3.9 $ 100.4      
Expenses related to sale of stock | $ $ 0.3        
Additional offering expenses | $   $ 6.3      
Capitalized equity issuance costs | $         $ 2.2
Common stock shares issued (in shares)       11,950,000 0
Common stock, shares outstanding (in shares)       11,950,000 0
Treasury Stock | Class B Common Stock          
Class of Stock [Line Items]          
Conversion of stock, shares issued (in shares)     3,170,034    
IPO | Class A Common Stock          
Class of Stock [Line Items]          
Common stock shares sold (in shares) 700,000 11,250,000      
Shares issued, price per share (in dollars per share) | $ / shares $ 12.00 $ 12.00      
Capitalized equity issuance costs | $       $ 6.3  
Over-Allotment Option | Class A Common Stock          
Class of Stock [Line Items]          
Expenses related to sale of stock | $   $ 7.6