Stock-based compensation - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Jun. 29, 2019	Sep. 29, 2018
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	48 months
Unrecognized stock-based compensation expense	$ 51.4	$ 71.5
Unrecognized stock-based compensation expense, period of recognition	2 years 2 months 12 days	2 years 7 months 6 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 55.1
Unrecognized stock-based compensation expense, period of recognition	3 years 7 months 6 days
2003 Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period	10 years

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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 (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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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

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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