Other Postretirement Benefits - Changes in the Benefit Obligations Recognized in Other Comprehensive Income (Details) - Other Postretirement Benefit Plans - USD ($) $ in Thousands	12 Months Ended
	Dec. 26, 2021	Dec. 27, 2020	Dec. 29, 2019
Other Postretirement Benefits
Net actuarial loss	$ 2,254	$ 4,044	$ 296
Amortization of loss	(3,407)	(3,051)	(3,375)
Amortization of prior service credit	3,098	4,225	4,766
Total recognized in other comprehensive income	1,945	5,218	1,687
Net periodic postretirement benefit cost/(income)	927	(119)	238
Total recognized in net periodic postretirement benefit cost/(income) and other comprehensive loss	$ 2,872	$ 5,099	$ 1,925