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

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

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The number of new shares issued in the conversion of stock in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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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.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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

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Net loss per share - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	Aug. 06, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 29, 2018	Sep. 30, 2017	Oct. 01, 2016	Oct. 03, 2015
Earnings Per Share [Abstract]
Common shares issued in conversion of outstanding shares of redeemable convertible preferred stock (shares)	32,482,590
Numerator:
Net loss attributable to common stockholders—basic and diluted		$ (1,720)	$ (26,988)	$ (32,592)	$ 45,697	$ (14,906)	$ (14,539)	$ (19,790)	$ 35,017	$ (15,604)	$ (14,217)	$ (38,214)	$ (68,777)
Denominator:
Weighted-average shares of common stock—basic and diluted (in shares)										65,706,215	56,314,546	53,873,051
Net loss per share attributable to common stockholders:
Basic and diluted (in USD per share)										$ (0.24)	$ (0.25)	$ (0.71)