Pension Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Defined Benefit Plan Disclosure [Line Items]
Pension settlement charge			$ 900	$ 0
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 720	$ 987	2,160	2,958
Expected return on plan assets	(321)	(432)	(961)	(1,293)
Amortization of net loss (gain)	862	867	2,586	2,600
Pension settlement charge	900	0	900	0
Net periodic benefit cost	2,161	1,422	4,685	4,265
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	38	69	113	206
Amortization of prior service credits	(125)	(125)	(373)	(374)
Amortization of net loss (gain)	(196)	(190)	(590)	(570)
Net periodic benefit cost	$ (283)	$ (246)	$ (850)	$ (738)