Goodwill and Intangible Assets - Activity of Goodwill by Reportable Operating Segment (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jul. 03, 2020	Jan. 03, 2020	Oct. 02, 2020	Sep. 27, 2019
Goodwill [Roll Forward]
Balance, beginning		$ 612.2	$ 612.2	$ 293.6
Business combinations			15.7	372.3
Impairment charges	$ 50.5			50.5
Measurement period adjustment to a business combination prior year		(4.8)	(1.8)	(2.2)
Foreign currency translation adjustments			(2.2)	(1.0)
Balance, ending			623.9	612.2
Oncology Systems
Goodwill [Roll Forward]
Balance, beginning		447.9	447.9	242.1
Business combinations			15.7	208.0
Impairment charges				0.0
Measurement period adjustment to a business combination prior year			(5.6)	(2.2)
Foreign currency translation adjustments			(3.3)	0.0
Balance, ending			454.7	447.9
Proton Solutions
Goodwill [Roll Forward]
Balance, beginning		0.0	0.0	51.5
Business combinations			0.0	0.0
Impairment charges				50.5
Measurement period adjustment to a business combination prior year			0.0	0.0
Foreign currency translation adjustments			0.0	(1.0)
Balance, ending			0.0	0.0
Other
Goodwill [Roll Forward]
Balance, beginning		$ 164.3	164.3	0.0
Business combinations			0.0	164.3
Impairment charges				0.0
Measurement period adjustment to a business combination prior year			3.8	0.0
Foreign currency translation adjustments			1.1	0.0
Balance, ending			$ 169.2	$ 164.3