Funded Status of Defined Benefit Pension and Post-Retirement Plans (Detail) - USD ($) $ in Thousands	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 469,801	$ 457,575
Pension Plan | Benefit Obligation
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	(495,387)	(509,256)	$ (505,298)
Pension Plan | Plan Assets - Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	469,801	457,575	425,781
Pension Plan | Funded Status
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	469,801	457,575
Benefit obligations	(495,387)	(509,256)
Net amount recognized	(25,586)	(51,681)
Other Postretirement Benefit Plan | Benefit Obligation
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations	(12,920)	(13,542)	(13,236)
Other Postretirement Benefit Plan | Plan Assets - Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	$ 0
Other Postretirement Benefit Plan | Funded Status
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Benefit obligations	(12,920)	(13,542)
Net amount recognized	$ (12,920)	$ (13,542)