Amounts Reclassified Out of Accumulated Other Comprehensive Income - Reclassification out of accumulated other comprehensive (loss) income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2018	Mar. 25, 2017	Mar. 31, 2018	Mar. 25, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance beginning		$ (28,055)	$ (44,434)	$ (28,812)	$ (45,832)
Other comprehensive income before reclassifications		0	(5)	0	(10)
Reclassifications to earnings		757	1,218	1,514	2,621
Other comprehensive income		757	1,213	1,514	2,611
Balance ending		(27,298)	(43,221)	(27,298)	(43,221)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance beginning		0	(10)	0	(205)
Other comprehensive income before reclassifications		0	(5)	0	(10)
Reclassifications to earnings	[1]	0	15	0	215
Other comprehensive income		0	10	0	205
Balance ending		0	0	0	0
Pension Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance beginning		(36,390)	(50,091)	(37,311)	(51,391)
Other comprehensive income		921	1,300	1,842	2,600
Balance ending		(35,469)	(48,791)	(35,469)	(48,791)
Amortization of Net Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications to earnings	[2]	921	1,300	1,842	2,600
Post-Retirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance beginning		8,335	5,667	8,499	5,764
Other comprehensive income		(164)	(97)	(328)	(194)
Balance ending		8,171	5,570	8,171	5,570
Amortization of Net (Gain) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications to earnings	[2]	$ (164)	$ (97)	$ (328)	$ (194)

[1] Reclassification of realized losses on cash flow hedges are recognized in interest expense.

[2] These amounts are included in the computation of net periodic benefit cost. See Note 13, “Pension Plans and Other Postretirement Benefits.”