Pension and Other Postretirement Benefit Plans - Schedule of Pension Plans' Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 27, 2020	Mar. 29, 2019	Mar. 27, 2020	Mar. 29, 2019
Component:
Service cost	$ 1,465	$ 2,127	$ 2,930	$ 4,333
Interest cost	13,031	17,715	26,062	35,828
Expected return on plan assets	(27,665)	(26,709)	(55,330)	(53,418)
Amortization of previously unrecognized items	3,110	3,489	6,220	6,171
Plan Amendment and settlement loss (gain)	0	(32,449)	2,651	(34,621)
Net periodic benefit cost	$ (10,059)	$ (35,827)	$ (17,467)	$ (41,707)