Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Oct. 02, 2020	Sep. 27, 2019	Sep. 28, 2018
Income Statement [Abstract]
Revenue	$ 530,037	$ 499,708	$ 570,398
Cost of revenue	259,871	279,000	324,692
Gross profit	270,166	220,708	245,706
Operating expenses:
Research and development	141,333	163,469	177,713
Selling, general and administrative	124,306	153,286	161,673
Impairment charges	0	264,786	6,575
Restructuring charges	1,139	19,543	6,265
Total operating expenses	266,778	601,084	352,226
Income (loss) from operations	3,388	(380,376)	(106,520)
Other (expense) income:
Warrant liability (expense) gain	(12,948)	765	27,646
Interest expense, net	(27,380)	(35,803)	(31,338)
Other expense	(4,622)	(7,739)	(45,023)
Total other expense, net	(44,950)	(42,777)	(48,715)
Loss before income taxes	(41,562)	(423,153)	(155,235)
Income tax expense (benefit)	4,516	(39,355)	(21,473)
Loss from continuing operations	(46,078)	(383,798)	(133,762)
Loss from discontinued operations	0	0	(6,215)
Net loss	$ (46,078)	$ (383,798)	$ (139,977)
Basic loss per share:
Loss from continuing operations (in USD per share)	$ (0.69)	$ (5.84)	$ (2.07)
Loss from 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:
Loss from continuing operations (in USD per share)	(0.69)	(5.84)	(2.47)
Loss from discontinued operations (in USD per share)	0	0	(0.10)
Loss per share-diluted (in USD per share)	$ (0.69)	$ (5.84)	$ (2.57)
Shares used:
Basic (in shares)	66,606	65,686	64,741
Diluted (in shares)	66,606	65,686	65,311