Balance sheet components - Finite-lived intangible assets, future amortization expense (Details) - USD ($) $ in Thousands	9 Months Ended
Jun. 27, 2020	Sep. 28, 2019
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross carrying amount	$ 7,622
Accumulated amortization	(940)
Finite-lived intangible assets, net carrying value	6,682
Intangible assets, gross carrying amount (excluding goodwill)	27,722
Intangible assets, net carrying value (excluding goodwill)	$ 26,782	$ 13
Weighted-average remaining life	3 years 9 months 14 days
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Remainder of fiscal 2020	$ 475
2021	1,899
2022	1,883
2023	1,235
2024	1,020
2025	170
Finite-lived intangible assets, net carrying value	6,682
In progress research and development
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets (excluding goodwill)	20,100
Technology
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross carrying amount	7,583
Accumulated amortization	(929)
Finite-lived intangible assets, net carrying value	$ 6,654
Weighted-average remaining life	3 years 9 months 18 days
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Finite-lived intangible assets, net carrying value	$ 6,654
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross carrying amount	39
Accumulated amortization	(11)
Finite-lived intangible assets, net carrying value	$ 28
Weighted-average remaining life	1 year 5 months 1 day
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Finite-lived intangible assets, net carrying value	$ 28

Finite-Lived Intangible Asset, Expected Amortization, After Year Four

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- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, 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 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
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- Definition

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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- Definition

Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in remainder of current fiscal year.

+ References

No definition available.

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- Definition

Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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- Definition

Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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- Definition

Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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- References

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- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 928
-SubTopic 340
-Section 50
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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.

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No definition available.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

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- Definition

Amount before accumulated amortization of intangible assets, excluding goodwill.

+ References

No definition available.

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- Definition

Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

+ References

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