Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation - Additional Information 1 (Detail)

v3.8.0.1
Stock-Based Compensation - Additional Information 1 (Detail)
$ / shares in Units, shares in Thousands, $ in Millions
12 Months Ended
Sep. 30, 2017
USD ($)
Installment
$ / shares
shares
Sep. 24, 2016
USD ($)
$ / shares
shares
Sep. 26, 2015
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend during expected term (in usd per share) $ 0    
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of vesting installments | Installment 4    
Expiration period approximately 6 years    
Expected life of option award 3 years 8 months 3 years 8 months 3 years 7 months 6 days
Stock price volatility (percent) 31.50% 30.80% 30.30%
Risk free interest rates (percent) 2.00% 1.30% 1.30%
Weighted average grant date fair value of options granted (in usd per share) $ 8.14 $ 3.04 $ 2.51
Total intrinsic value of options exercised | $ $ 44.0 $ 22.6 $ 5.9
Total unrecognized compensation cost | $ $ 7.4    
Nonvested stock options remaining weighted average vesting period 3 years    
Stock Options | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding options to purchase common stock (in usd per share) $ 6.43 $ 6.43 $ 6.43
Stock Options | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding options to purchase common stock (in usd per share) $ 33.15 $ 15.56 $ 15.00
Restricted Stock Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total unrecognized compensation cost | $ $ 11.1    
Nonvested stock options remaining weighted average vesting period 3 years    
Restricted stock awards outstanding, shares | shares 1,137 1,540  
Restricted Stock Awards | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share based payment award vesting conditional period of employment 4 years    
Restricted Stock Awards | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share based payment award vesting conditional period of employment 5 years