Restructuring and Severance Charges - Additional Information (Detail) Person in Thousands, $ in Millions	12 Months Ended
	Sep. 27, 2015 USD ($) Person	Sep. 28, 2014 USD ($)	Sep. 29, 2013 USD ($)
Schedule of Status of Facilities by Location [Line Items]
Recorded severance accruals	$ 3.4	$ 3.8
Restructuring and severance charges	15.4	31.5	$ 9.9
Employee Severance
Schedule of Status of Facilities by Location [Line Items]
Restructuring, Reversal of Prior Provision	10.0
Restructuring, Settlement and Impairment Provisions	$ 10.6
Number of employees | Person	250
Contract Termination Costs
Schedule of Status of Facilities by Location [Line Items]
Restructuring, Settlement and Impairment Provisions	$ 2.6
Restructuring Reserve, Accrual Adjustment	(1.1)
Other Associated Costs
Schedule of Status of Facilities by Location [Line Items]
Restructuring, Settlement and Impairment Provisions	3.9
Other Facilities
Schedule of Status of Facilities by Location [Line Items]
Restructuring, Settlement and Impairment Provisions	17.1
Restructuring Reserve, Accrual Adjustment	(1.7)
Payments for Restructuring	19.5
Restructuring Reserve, Settled without Cash	2.2
Recorded severance accruals	6.2	12.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restructuring Liabilities	0.1
Other Facilities | Employee Severance
Schedule of Status of Facilities by Location [Line Items]
Restructuring Reserve, Accrual Adjustment	(0.6)
Payments for Restructuring	11.3
Restructuring Reserve, Settled without Cash	0.0
Recorded severance accruals	2.9	4.1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restructuring Liabilities	0.1
Other Facilities | Contract Termination Costs
Schedule of Status of Facilities by Location [Line Items]
Payments for Restructuring	5.9
Restructuring Reserve, Settled without Cash	0.6
Recorded severance accruals	3.2	8.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restructuring Liabilities	0.0
Other Facilities | Other Associated Costs
Schedule of Status of Facilities by Location [Line Items]
Restructuring Reserve, Accrual Adjustment	0.0
Payments for Restructuring	2.2
Restructuring Reserve, Settled without Cash	1.6
Recorded severance accruals	0.1	$ 0.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restructuring Liabilities	0.0
Vitesse | Employee Severance
Schedule of Status of Facilities by Location [Line Items]
Restructuring and severance charges	$ 2.9