Postretirement Benefits - Net Periodic Benefit Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 27, 2020	Mar. 29, 2019	Mar. 27, 2020	Mar. 29, 2019
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 935	$ 1,166	$ 1,870	$ 2,332
Expected return on plan assets	(1,583)	(1,593)	(3,166)	(3,186)
Amortization of actuarial loss	222	25	444	50
Net periodic benefit credit	$ (426)	$ (402)	$ (852)	$ (804)