Goodwill and Intangible Assets - Changes in Carrying Value of Goodwill (Details) - USD ($)		3 Months Ended		12 Months Ended
	Jun. 29, 2020	Sep. 27, 2020	Sep. 29, 2019	Sep. 27, 2020	Sep. 29, 2019	Sep. 30, 2018
Goodwill [Roll Forward]
Balance at beginning of the period				$ 924,820,000	$ 798,820,000
Acquisitions				80,176,000	146,699,000
Impairment	$ 0	$ (15,800,000)	$ (7,800,000)	(15,800,000)	(7,755,000)	$ 0
Translation and other				4,302,000	(12,944,000)
Balance at end of the period		993,498,000	924,820,000	993,498,000	924,820,000	798,820,000
GSG
Goodwill [Roll Forward]
Balance at beginning of the period				441,802,000	389,741,000
Acquisitions				74,882,000	53,098,000
Impairment				0	0
Translation and other				(369,000)	(1,037,000)
Balance at end of the period		516,315,000	441,802,000	516,315,000	441,802,000	389,741,000
CIG
Goodwill [Roll Forward]
Balance at beginning of the period				483,018,000	409,079,000
Acquisitions				5,294,000	93,601,000
Impairment				(15,800,000)	(7,755,000)
Translation and other				4,671,000	(11,907,000)
Balance at end of the period		$ 477,183,000	$ 483,018,000	$ 477,183,000	$ 483,018,000	$ 409,079,000