Postretirement Benefits - Net Periodic Benefit Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 26, 2020	Jun. 28, 2019	Jun. 26, 2020	Jun. 28, 2019
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 935	$ 1,166	$ 2,805	$ 3,498
Expected return on plan assets	(1,583)	(1,593)	(4,749)	(4,779)
Amortization of actuarial loss	222	25	666	75
Net periodic benefit credit	$ (426)	$ (402)	$ (1,278)	$ (1,206)