Pension Benefits - Change in Benefit Obligation and Plan Assets Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 27, 2020	Dec. 29, 2019	Oct. 31, 2020	Dec. 30, 2018
Pension Benefits
Benefit obligation			$ 236,300
Pension Plan
Pension Benefits
Benefit obligation	$ 1,808,605	$ 1,908,035		$ 1,714,464
Settlements	236,282	0
Actuarial gain (loss)	(174,288)	(223,978)
Accumulated benefit obligation	$ 1,800,000	$ 1,900,000