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Stockholders' Equity and Stock-Based Compensation - Assumptions to Value Stock Options (Detail) - USD ($)
3 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 29, 2018
Sep. 24, 2016
Assumptions:      
Risk-free interest rates 1.80% 2.10% 1.60%
Expected life (in years) 4 years 8 months 15 days 4 years 8 months 15 days 4 years 8 months 15 days
Expected volatility 36.60% 35.30% 37.80%
Dividend yield $ 0 $ 0 $ 0
ESPP      
Assumptions:      
Risk-free interest rates 0.72% 1.62% 0.34%
Expected life (in years) 6 months 6 months 6 months
Expected volatility 24.90% 25.00% 27.20%
Dividend yield $ 0 $ 0 $ 0