Business Segments and Geographic Information - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Sep. 26, 2015 USD ($)	Jun. 27, 2015 USD ($)	Mar. 28, 2015 USD ($)	Dec. 27, 2014 USD ($)	Sep. 27, 2014 USD ($)	Jun. 28, 2014 USD ($)	Mar. 29, 2014 USD ($)	Dec. 28, 2013 USD ($)	Sep. 26, 2015 USD ($) Segment	Sep. 27, 2014 USD ($)	Sep. 28, 2013 USD ($)
Segment Reporting Disclosure [Line Items]
Number of reportable segments | Segment									4
Revenues	$ 702,800,000	$ 693,900,000	$ 655,500,000	$ 652,800,000	$ 660,600,000	$ 632,600,000	$ 625,000,000	$ 612,400,000	$ 2,705,000,000	$ 2,530,700,000	$ 2,492,300,000
Impairment of goodwill									0	0	1,117,400,000
Intersegment [Member]
Segment Reporting Disclosure [Line Items]
Revenues	$ 0				$ 0				0	0
Diagnostics [Member]
Segment Reporting Disclosure [Line Items]
Revenues									$ 1,211,800,000	$ 1,186,800,000	$ 1,189,800,000