Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 27, 2019	Jun. 28, 2019	Mar. 29, 2019	Dec. 28, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Sep. 27, 2019	Sep. 28, 2018	Sep. 29, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 878,900	$ 825,800	$ 779,400	$ 741,000	$ 801,600	$ 709,100	$ 729,900	$ 678,500	$ 3,225,100	$ 2,919,100	$ 2,619,300
Gross margin	384,600	351,400	318,200	316,100	338,700	313,600	318,500	302,800	1,370,300	1,273,600	1,113,900
Net earnings (loss)	70,400	29,500	88,400	103,900	116,800	72,500	73,200	(112,200)	292,200	150,300	226,000
Net earnings attributable to Varian	$ 70,700	$ 29,400	$ 88,600	$ 103,200	$ 116,400	$ 72,600	$ 73,200	$ (112,300)	$ 291,900	$ 149,900	$ 218,500
Net earnings per share - basic (in dollars per share)	$ 0.78	$ 0.32	$ 0.97	$ 1.13	$ 1.27	$ 0.79	$ 0.80	$ (1.22)	$ 3.21	$ 1.64	$ 2.36
Net earnings per share - diluted (in dollars per share)	$ 0.77	$ 0.32	$ 0.96	$ 1.12	$ 1.26	$ 0.79	$ 0.79	$ (1.22)	$ 3.18	$ 1.62	$ 2.35
Gain on sale of investment				$ 22,000					$ 21,800	$ 0	$ 0
Goodwill impairment charge		$ 50,500							50,500	0	0
Write-off of in-process research and development related to acquisition-related activities		$ 20,800							20,800	0	0
Change in fair value of contingent consideration	$ 18,600			$ 11,600					18,600	0	300
Tax benefit related to change in law related to the Act					$ (7,100)			$ 207,100
Loss on hedges related to acquisition-related activities						$ 13,300	$ 16,400
Impairment charges						11,000	$ 11,100		$ 50,600	$ 22,400	$ 51,400
Acquisition costs						8,400
Breakup fee from Sirtex						$ 9,000
Tax benefit due to partial release of a valuation allowance					$ 8,000