Pension Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Jun. 26, 2021	Mar. 27, 2021	Jun. 27, 2020	Jun. 26, 2021	Jun. 27, 2020	Jun. 27, 2020
Defined Benefit Plan Disclosure [Line Items]
Pension settlement charge				$ 712	$ 900
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 534		$ 720	1,602		$ 2,160
Expected return on plan assets	(319)		(321)	(957)		(961)
Amortization of net loss (gain)	899		862	2,695		2,586
Pension settlement charge	142	$ 570	900	712		900
Net periodic benefit cost	1,256		2,161	4,052		4,685
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	20		38	58		113
Amortization of prior service credits	(124)		(125)	(373)		(373)
Amortization of net loss (gain)	(182)		(196)	(543)		(590)
Net periodic benefit cost	$ (286)		$ (283)	$ (858)		$ (850)