Employee Retirement and Pension Benefits - Components of Pension Benefit/ Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Retirement Benefits [Abstract]
Administrative cost	$ 775	$ 1,250	$ 2,325	$ 3,750
Interest cost	3,050	3,725	9,150	11,175
Expected return on plan assets	(5,475)	(4,650)	(16,425)	(13,950)
Amortization of net actuarial pension loss	1,725	2,225	5,175	6,675
Pension benefit expense	$ 75	$ 2,550	$ 225	$ 7,650