Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 27, 2020	Sep. 27, 2020	Jun. 28, 2020	Mar. 29, 2020	Dec. 29, 2019	Sep. 29, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 27, 2020	Dec. 29, 2019	Dec. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other components of net periodic benefit costs	$ (82,419)	$ (2,272)	$ (2,149)	$ (2,314)	$ (1,800)	$ (1,834)	$ (1,833)	$ (1,835)	$ (89,154)	$ (7,302)	$ (8,274)
Total reclassification, before tax	6,268	40,861	29,443	38,860	75,917	22,497	34,586	31,460	115,432	164,460	176,091
Income tax expense/(benefit)	(4,475)	7,283	5,781	6,006	$ 7,705	$ 6,070	$ 9,415	$ 1,304	14,595	24,494	48,631
Total reclassification, net of tax	$ 10,743	$ 33,578	$ 23,662	$ 32,854					100,837	$ 139,966	$ 127,460
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassification, before tax									105,531
Income tax expense/(benefit)									28,323
Total reclassification, net of tax									77,208
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other components of net periodic benefit costs									(6,119)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other components of net periodic benefit costs									31,009
Reclassification out of Accumulated Other Comprehensive Income | Pension settlement charge
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other components of net periodic benefit costs									$ 80,641