Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity - Additional Information (Detail)

v3.8.0.1
Shareholders' Equity - Additional Information (Detail)
 12 Months Ended
Sep. 30, 2017
USD ($)
vote
$ / shares
shares
Sep. 24, 2016
$ / shares
shares
Sep. 24, 2011
USD ($)
Class of Stock [Line Items]      
Preferred stock authorized (in shares) 1,000,000 1,000,000  
Preferred stock, par value (in usd per share) | $ / shares $ 0.01 $ 0.01  
Preferred stock, shares outstanding 0 0  
Common stock      
Class of Stock [Line Items]      
Common stock authorized (in shares) 80,000,000 80,000,000  
Common stock, par value (in usd per share) | $ / shares $ 0.01 $ 0.01  
Common stock, shares outstanding 12,160,023 11,998,472  
Authorized amount to repurchase stock | $     $ 100,000,000
Aggregate stock repurchased shares 7,900,000    
Aggregate stock repurchased value | $ $ 65,000,000    
Class A common stock      
Class of Stock [Line Items]      
Common stock authorized (in shares) 100,000,000 100,000,000  
Common stock, par value (in usd per share) | $ / shares $ 0.01 $ 0.01  
Common stock, shares outstanding 38,019,736 37,418,572  
Class B stock      
Class of Stock [Line Items]      
Common stock authorized (in shares) 3,000,000 3,000,000  
Common stock, par value (in usd per share) | $ / shares $ 0.01 $ 0.01  
Common stock, shares outstanding 1,652,262 1,652,262  
Percentage of vote cast for shares (percent) 49.00%    
Convertible shares conversion ratio 1    
Minimum | Class B stock      
Class of Stock [Line Items]      
Number of voting powers | vote 1    
Maximum | Class B stock      
Class of Stock [Line Items]      
Number of voting powers | vote 10