Net loss per share attributable to common stockholders - Computation of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Sep. 28, 2019	Sep. 29, 2018	Sep. 30, 2017
Numerator:
Net loss attributable to common stockholders - basic and diluted	$ (4,766)	$ (15,604)	$ (14,217)
Denominator:
Weighted-average shares of common stock—basic and diluted (in shares)	103,783,006	65,706,215	56,314,546
Net loss per share attributable to common stockholders:
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.05)	$ (0.24)	$ (0.25)

Net Income (Loss) Available to Common Stockholders, Basic and Diluted [Abstract]

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- Definition

Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]

+ References

No definition available.

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- Definition

The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=117326831&loc=d3e1337-109256

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- Definition

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=117326831&loc=d3e1377-109256

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- Definition

Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

+ References

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