Goodwill and Intangible Assets Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Mar. 26, 2021	Dec. 25, 2020	Mar. 27, 2020	Mar. 26, 2021	Mar. 27, 2020	Sep. 25, 2020
Finite-Lived Intangible Assets [Line Items]
Cost	$ 430,529			$ 430,529		$ 430,346
Accumulated Amortization	(293,585)			(293,585)		(277,915)
Total	136,944			136,944		152,431
Purchases of intangible assets		$ 2,900
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		14 years
Amortization of Intangible Assets	7,300		$ 7,600	14,600	$ 14,800
Acquired Patents And Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	342,807			342,807		342,637
Accumulated Amortization	(220,006)			(220,006)		(206,123)
Total	122,801			122,801		136,514
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	64,746			64,746		64,740
Accumulated Amortization	(50,807)			(50,807)		(49,062)
Total	13,939			13,939		15,678
Other Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	22,976			22,976		22,969
Accumulated Amortization	(22,772)			(22,772)		(22,730)
Total	$ 204			$ 204		$ 239