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Income taxes - Valuation allowance (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 28, 2019 | Sep. 29, 2018 | Sep. 30, 2017
Valuation Allowance [Roll Forward] |  |  |
Beginning balance | $ 72,380 | $ 94,956 | $ 95,882
Increase (decrease) during the period | 22,708 | (22,576) | (926)
Ending balance | $ 95,088 | $ 72,380 | $ 94,956

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- Definition Deferred Tax Assets, Valuation Allowance [Roll Forward] + References No definition available. + Details
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Namespace Prefix: | sono_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=116821951&loc=d3e32123-109318 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration