Restructuring and Divestiture Charges - Additional Information (Detail)	3 Months Ended										12 Months Ended
	Sep. 24, 2016 USD ($)	Mar. 26, 2016 USD ($)	Dec. 26, 2015 USD ($)	Sep. 26, 2015 USD ($)	Jun. 27, 2015 USD ($)	Dec. 27, 2014 USD ($)	Sep. 27, 2014 USD ($)	Dec. 28, 2013 USD ($) employee	Mar. 30, 2013 USD ($)	Sep. 29, 2012 USD ($)	Sep. 24, 2016 USD ($)	Sep. 26, 2015 USD ($)	Sep. 27, 2014 USD ($)	Sep. 28, 2013 USD ($)	Sep. 29, 2012 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and divestiture charges	$ 2,900,000	$ 3,800,000	$ 2,300,000	$ 6,500,000	$ 11,900,000	$ 8,000,000					$ 10,500,000	$ 28,500,000	$ 51,700,000
Impairment charges of equipment fair value								$ 3,100,000
Loss on sale of business							$ 5,300,000				0	(9,600,000)	(5,500,000)
Restructuring Reserve, Translation and Other Adjustment					$ 9,600,000
Restructuring Charges [Member] | San Diego [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges	900,000
Expected Future Charges											200,000
Restructuring Charges [Member] | Bedford [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges											1,700,000
severance and benefits and facility closure costs											0
Restructuring Charges [Member] | International [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges											7,900,000
Compensation charges											400,000
Restructuring Charges [Member] | Fiscal 2015 Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and divestiture charges												28,500,000
Reduction Of Workforce Expenses												16,300,000
Facility Closure Costs												2,600,000
Fiscal 2015 Actions [Member] | Restructuring Charges [Member] | Fiscal 2015 Charges [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges												0
Compensation charges												4,100,000
Reduction Of Workforce Expenses												10,000,000
Facility Closure Costs												0
Fiscal 2014 Actions [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges								6,300,000					16,600,000
Compensation charges								400,000					1,800,000
Fiscal 2014 Actions [Member] | Jack Cumming [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges								6,600,000
Compensation charges								$ 4,400,000
Fiscal 2014 Actions [Member] | Restructuring Charges [Member] | Fiscal 2015 Charges [Member]
Restructuring Cost and Reserve [Line Items]
Reduction Of Workforce Expenses												6,000,000
Facility Closure Costs												$ 2,000,000
Number Office Locations related to Facility Closure Costs												0
Consolidation of Diagnostics Operations [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges											0	$ 0
severance and benefits and facility closure costs													0
Employee retention program, payments in cash									$ 9,700,000
Consolidation of Diagnostics Operations [Member] | Molecular Diagnostics Operations [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges												100,000	3,000,000	$ 3,200,000	$ 900,000
severance and benefits and facility closure costs											0
Facility Closure Costs												500,000
Exiting charges										$ 600,000
Consolidation of Diagnostics Operations [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges														10,800,000	13,300,000
Compensation charges														$ 6,300,000	$ 3,500,000
Consolidation of Diagnostics Operations [Member] | Restructuring Charges [Member] | Fiscal 2015 Charges [Member]
Restructuring Cost and Reserve [Line Items]
Reduction Of Workforce Expenses												100,000
Facility Closure Costs												500,000
Other Operating Cost Reductions [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges												300,000	$ 8,700,000
Number of employees affected for severance benefits | employee								95
Impairment charges of equipment fair value								$ 3,100,000
Other Operating Cost Reductions [Member] | Restructuring Charges [Member] | Fiscal 2015 Charges [Member]
Restructuring Cost and Reserve [Line Items]
Reduction Of Workforce Expenses												200,000
Facility Closure Costs												$ 100,000
Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Capital Lease Obligations, Current	8,000,000										8,000,000
Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Capital Lease Obligations, Current	$ 12,000,000										$ 12,000,000