Net Periodic Pension Cost for Defined Benefit Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 15,790	$ 15,108	$ 12,861
Interest cost	17,057	15,553	18,095
Expected return on plan assets	(27,918)	(25,866)	(24,491)
Settlement	0	21	2
Amortization of prior service cost	499	490	487
Amortization of actuarial (gain) loss	3,275	7,643	6,590
Net periodic cost (benefit)	8,703	12,949	13,544
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	361	385	342
Interest cost	402	335	473
Expected return on plan assets	0	0	0
Settlement	0	0	0
Amortization of prior service cost	(5)	(5)	(17)
Amortization of actuarial (gain) loss	0	0	0
Net periodic cost (benefit)	$ 758	$ 715	$ 798