Quarterly Financial Data - Schedule of Quarterly Financial Data (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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 147,249	$ 137,267	$ 126,424	$ 119,097	$ 112,248	$ 108,306	$ 128,465	$ 150,689	$ 530,037	$ 499,708	$ 570,398
Gross profit	77,716	70,876	63,370	58,204	52,925	33,828	57,330	76,625	270,166	220,708	245,706
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)
Per share data
Loss from 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)
Per share data
Loss from 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)
Warrant liability gain	$ 2,000		$ 8,600			$ 1,900		$ 5,500