Restructuring (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 27, 2020	Mar. 29, 2019	Mar. 27, 2020	Mar. 29, 2019	Sep. 27, 2019
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			$ 15,851	$ 124	$ 124
Restructuring charges	$ 331	$ (18)	(344)	(32)	(36,558)
Cash payments			(19,679)		(7,713)
Non-cash and other adjustments			3,533		(13,118)
Restructuring reserve, ending balance	49		49		15,851
Severance
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			128	0	0
Restructuring charges			0		(3,134)
Cash payments			(75)		(3,006)
Non-cash and other adjustments			(4)		0
Restructuring reserve, ending balance	49		49		128
Leased facility exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			15,723	0	0
Restructuring charges			(344)		(18,261)
Cash payments			(19,604)		(4,577)
Non-cash and other adjustments			3,537		2,039
Restructuring reserve, ending balance	0		0		15,723
Fixed assets write-off
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			0	0	0
Restructuring charges			0		(15,216)
Cash payments			0		0
Non-cash and other adjustments			0		(15,216)
Restructuring reserve, ending balance	0		0		0
Other associated costs
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance			0	$ 124	124
Restructuring charges			0		53
Cash payments			0		(130)
Non-cash and other adjustments			0		59
Restructuring reserve, ending balance	$ 0		$ 0		$ 0