Pension, Postretirement and Postemployment Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($)	12 Months Ended
	Dec. 27, 2020	Dec. 29, 2019	Dec. 30, 2018
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0	$ 1,168,000	$ 1,300,000
Interest cost	1,466,000	6,624,000	13,358,000
Expected return on assets	0	(6,163,000)	(18,475,000)
Amortization of prior service cost	(11,000)	(11,000)	0
Curtailment/Settlement losses	715,000	7,578,000	10,995,000
Curtailment/Settlement losses	0	110,962,000	0
Net periodic benefit cost (income)	2,170,000	120,158,000	7,178,000
Postretirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	888,000	756,000
Interest cost	919,000	1,267,000	1,171,000
Curtailment/Settlement losses	0	21,000	165,000
Net periodic benefit cost (income)	$ 919,000	$ 2,176,000	$ 2,092,000