Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 23, 2017	Sep. 29, 2018	Sep. 23, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of year			$ 693,756
Total other comprehensive income	$ 6,510	$ 2,032	(4,008)	$ 6,093
Balance, end of quarter	776,856		776,856
Unrecognized components of employee benefit plans, net of tax
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of year			(81,638)	(110,080)
Other comprehensive income (loss) before reclassifications			0	0
Income tax on other comprehensive income (loss)			0	0
Income tax on reclassifications			(2,028)	(3,353)
Total other comprehensive income			7,193	6,093
Balance, end of quarter	(74,445)	(103,987)	(74,445)	(103,987)
Amortization of losses
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Reclassifications to earnings			8,907	8,989
Amortization of prior service costs
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Reclassifications to earnings			429	572
Amortization of negative plan amendment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Reclassifications to earnings			(115)	(115)
Unrealized gain on derivative instruments, net of tax
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of year			619	0
Other comprehensive income (loss) before reclassifications			(664)	0
Income tax on other comprehensive income (loss)			281	0
Income tax on reclassifications			30	0
Total other comprehensive income			(936)	0
Balance, end of quarter	(317)	0	(317)	0
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of year			4,868	0
Total other comprehensive income			(10,265)	0
Balance, end of quarter	(5,397)	0	(5,397)	0
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, end of quarter	$ (80,159)	$ (103,987)	(80,159)	(103,987)
Interest rate swaps | Unrealized gain on derivative instruments, net of tax
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Reclassifications to earnings			112	0
Foreign exchange forward contracts | Unrealized gain on derivative instruments, net of tax
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Reclassifications to earnings			$ (695)	$ 0