Pension Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 26, 2020	Dec. 28, 2019
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 534	$ 720
Expected return on plan assets	(319)	(320)
Amortization of net loss (gain)	898	862
Net periodic benefit cost	1,113	1,262
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	19	37
Amortization of prior service credits	(124)	(124)
Amortization of net loss (gain)	(181)	(197)
Net periodic benefit cost	$ (286)	$ (284)