Amounts Reclassified Out of Accumulated Other Comprehensive Income - Reclassification out of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 27, 2021	Mar. 28, 2020	Mar. 27, 2021	Mar. 28, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance beginning		$ (25,183)	$ (25,645)	$ (25,776)	$ (26,186)
Recognition of net actuarial loss for pension settlement		570	0	570	0
Reclassifications to earnings		593	541	1,186	1,082
Other comprehensive income		1,163	541	1,756	1,082
Balance ending		(24,020)	(25,104)	(24,020)	(25,104)
Pension Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance beginning		(31,388)	(32,871)	(32,286)	(33,733)
Recognition of net actuarial loss for pension settlement	[1]	570	0	570	0
Reclassifications to earnings	[1]	898	862	1,796	1,724
Other comprehensive income		1,468	862	2,366	1,724
Balance ending		(29,920)	(32,009)	(29,920)	(32,009)
Post-Retirement Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance beginning		6,205	7,226	6,510	7,547
Amortization of net gain and prior service credits	[1]	(305)	(321)	(610)	(642)
Other comprehensive income		(305)	(321)	(610)	(642)
Balance ending		$ 5,900	$ 6,905	$ 5,900	$ 6,905

[1] These amounts are included in the computation of net periodic benefit cost.  See Note 15, “Pension Plans and Other Postretirement Benefits.”