Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended								12 Months Ended
	Jan. 28, 2017	Sep. 28, 2018 USD ($) customer	Jun. 29, 2018 USD ($)	Mar. 30, 2018 USD ($)	Dec. 29, 2017 USD ($)	Sep. 29, 2017 USD ($) customer	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 30, 2016 USD ($)	Sep. 28, 2018 USD ($) customer reporting_unit	Sep. 29, 2017 USD ($) customer	Sep. 30, 2016 USD ($) customer	Sep. 30, 2017 USD ($)	Apr. 02, 1999 company
Significant Accounting Policies [Line Items]
Number of publicly traded companies | company														3
Number of publicly traded companies distributed to stockholders | company														2
Foreign currency gain (loss) before tax										$ 3,000,000	$ 3,000,000	$ 1,600,000
Impairment charges											51,400,000	0
Impairment of notes receivable			$ 11,000,000	$ 11,100,000		$ 13,100,000			$ 38,300,000	$ 22,400,000	51,400,000	2,200,000
Number of reporting units tested for impairment of goodwill | reporting_unit										2
Warranty period										12 months
VPT fair value in excess of carrying amount (percent)		48.00%								48.00%
Decrease to net revenues		$ 801,600,000	$ 709,100,000	$ 729,900,000	$ 678,500,000	$ 721,800,000	$ 632,800,000	$ 663,200,000	$ 601,500,000	$ 2,919,100,000	$ 2,619,300,000	$ 2,593,700,000
Minimum
Significant Accounting Policies [Line Items]
Manufacturing, Commissioning and Installation Period										18 months
Finite-lived intangible asset, useful life (in years)										2 years
Maximum
Significant Accounting Policies [Line Items]
Manufacturing, Commissioning and Installation Period										24 months
Finite-lived intangible asset, useful life (in years)										10 years
Land Improvements
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)										15 years
Building | Minimum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)										20 years
Building | Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)										30 years
Machinery and Equipment | Minimum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)										3 years
Machinery and Equipment | Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)										7 years
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Varex Imaging
Significant Accounting Policies [Line Items]
Number of new shares distributed for every existing share (shares)	0.4
Accounts Receivable
Significant Accounting Policies [Line Items]
Number of customers representing more than 10% | customer		0				0				0	0	0
Notes Receivable
Significant Accounting Policies [Line Items]
Impairment of notes receivable										$ 22,100,000
C P T C
Significant Accounting Policies [Line Items]
Equity ownership (percent)		47.08%								47.08%
Retained Earnings | Accounting Standards Update 2016-09, Forfeiture Rate [Member]
Significant Accounting Policies [Line Items]
Cumulative effect of new accounting principle													$ 400,000