Employee Stock Plans - Fair Value with Weighted Average Assumptions (Detail) - $ / shares	12 Months Ended
Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Employee Stock Purchase Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	6 months
Risk-free interest rate	1.60%	0.70%	0.30%
Expected volatility	25.20%	20.30%	17.60%
Expected dividend	0.00%	0.00%	0.00%
Weighted average fair value at grant date (in USD per share)	$ 24.56	$ 18.92	$ 16.09
Employee Stock Option Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	3 years 9 months 29 days	3 years 11 months 27 days	4 years 1 month 18 days
Risk-free interest rate	2.30%	1.70%	1.10%
Expected volatility	19.10%	21.30%	20.10%
Expected dividend	0.00%	0.00%	0.00%
Weighted average fair value at grant date (in USD per share)	$ 20.88	$ 16.12	$ 13.71

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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