Goodwill and Intangible Assets Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 27, 2020	Dec. 27, 2019	Mar. 29, 2019	Dec. 28, 2018	Mar. 27, 2020	Mar. 29, 2019	Sep. 27, 2019
Finite-Lived Intangible Assets [Line Items]
Cost	$ 429,162				$ 429,162		$ 425,705
Accumulated Amortization	(261,245)				(261,245)		(244,814)
Total	167,917				167,917		180,891
Purchases of intangible assets	0	$ 2,900	$ 5,000	$ 12,100	$ 2,900	$ 17,100
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		14 years	4 years	11 years 7 months 6 days	14 years	9 years 3 months 18 days
Amortization of Intangible Assets	7,600		$ 7,400		$ 14,800	$ 14,100
Acquired Patents And Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	341,531				341,531		338,075
Accumulated Amortization	(191,399)				(191,399)		(176,867)
Total	150,132				150,132		161,208
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	64,705				64,705		64,728
Accumulated Amortization	(47,271)				(47,271)		(45,510)
Total	17,434				17,434		19,218
Other Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	22,926				22,926		22,902
Accumulated Amortization	(22,575)				(22,575)		(22,437)
Total	$ 351				$ 351		$ 465