Postretirement Benefits - Net Periodic Benefit Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended
	Dec. 27, 2019	Dec. 28, 2018
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 935	$ 1,166
Expected return on plan assets	(1,583)	(1,593)
Amortization of actuarial loss	222	25
Net periodic benefit credit	$ (426)	$ (402)