Other Postretirement Benefits - Changes in the Benefit Obligations Recognized in Other Comprehensive Income (Details) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Other Postretirement Benefits
Net actuarial loss/(gain)	$ (4,905)	$ (6,625)	$ 28
Amortization of loss	(4,735)	(3,621)	(4,105)
Amortization of prior service credit	6,157	7,755	8,440
Effect of curtailment	0	6,502	0
Effect of settlement	0	26,235	0
Total recognized in other comprehensive (income)/loss	(3,483)	30,246	4,363
Net periodic postretirement benefit cost/(income)	75	(34,623)	(1,939)
Total recognized in net periodic postretirement benefit cost/(income) and other comprehensive (income)/loss	(3,408)	(4,377)	2,424
Estimated actuarial loss that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	3,000
Estimated prior service cost that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	5,000
Additional postretirement costs	$ 16,000	$ 15,000	$ 15,000