Pension Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 27, 2021	Mar. 28, 2020	Mar. 27, 2021	Mar. 28, 2020
Defined Benefit Plan Disclosure [Line Items]
Pension settlement charge			$ 570	$ 0
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 534	$ 720	1,068	1,440
Expected return on plan assets	(319)	(320)	(638)	(640)
Amortization of net loss (gain)	898	862	1,796	1,724
Pension settlement charge	570	0	570	0
Net periodic benefit cost	1,683	1,262	2,796	2,524
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	19	38	38	75
Amortization of prior service credits	(125)	(125)	(249)	(249)
Amortization of net loss (gain)	(180)	(196)	(361)	(393)
Net periodic benefit cost	$ (286)	$ (283)	$ (572)	$ (567)