Stockholders' Equity and Stock-Based Compensation - Assumptions to Value Stock Options (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Assumptions:
Risk-free interest rates	1.80%	1.60%	1.70%
Expected life (in years)	4 years 8 months 15 days	4 years 8 months 15 days	5 years 4 months 6 days
Expected volatility	36.60%	37.80%	38.60%
Dividend yield	$ 0	$ 0	$ 0
Employee stock purchase plan [Member]
Assumptions:
Risk-free interest rates	0.72%	0.34%	0.10%
Expected life (in years)	6 months	6 months	6 months
Expected volatility	24.90%	27.20%	27.40%
Dividend yield	$ 0	$ 0	$ 0