Earnings Per Share - Computation for Basic and Diluted Net Income (Loss) Per Share of Common Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 02, 2020	Jul. 03, 2020	Apr. 03, 2020	Jan. 03, 2020	Sep. 27, 2019	Jun. 28, 2019	Mar. 29, 2019	Dec. 28, 2018	Oct. 02, 2020	Sep. 27, 2019	Sep. 28, 2018
Numerator:
Loss from continuing operations	$ 17,492	$ (24,982)	$ (10,226)	$ (28,362)	$ 10,516	$ (324,714)	$ (46,204)	$ (23,396)	$ (46,078)	$ (383,798)	$ (133,762)
Loss from discontinued operations									0	0	(6,215)
Net loss									(46,078)	(383,798)	(139,977)
Warrant liability gain									0	0	(27,646)
Net loss attributable to common stockholders									$ (46,078)	$ (383,798)	$ (167,623)
Denominator:
Weighted average common shares outstanding-basic (in shares)									66,606,000	65,686,000	64,741,000
Dilutive effect of warrants (in shares)									0	0	569,667
Weighted average common shares outstanding-diluted (in shares)									66,606,000	65,686,000	65,311,000
Basic loss per share:
Continuing operations (in USD per share)	$ 0.26	$ (0.37)	$ (0.15)	$ (0.43)	$ 0.16	$ (4.93)	$ (0.71)	$ (0.36)	$ (0.69)	$ (5.84)	$ (2.07)
Discontinued operations (in USD per share)									0	0	(0.10)
Loss per share-basic (in USD per share)									(0.69)	(5.84)	(2.16)
Diluted loss per share:
Continuing operations (in USD per share)	$ 0.22	$ (0.37)	$ (0.28)	$ (0.43)	$ 0.16	$ (4.95)	$ (0.71)	$ (0.44)	(0.69)	(5.84)	(2.47)
Discontinued operations (in USD per share)									0	0	(0.10)
Loss per share-diluted (in USD per share)									$ (0.69)	$ (5.84)	$ (2.57)