Stock-based compensation - Additional Information (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Mar. 30, 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	$ 58.3	$ 71.5
Unrecognized stock-based compensation expense, period of recognition	2 years 3 months 18 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	$ 50.1
Unrecognized stock-based compensation expense, period of recognition	3 years 9 months 18 days
2003 Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period	10 years

Unrecognized cost of unvested share-based compensation awards.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, 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
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-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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