Benefit Plans - Benefit Plan Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Components of net periodic benefit cost:
Service cost	$ 2,462	$ 2,040	$ 2,266
Interest cost	2,173	3,169	3,104
Expected return on plan assets	(1,972)	(3,187)	(3,222)
Amortization of prior service and net actuarial loss	963	243	291
Net periodic benefit cost	3,626	2,265	2,439
Net settlement loss	236	260	238
Total expense for the year	$ 3,862	$ 2,525	$ 2,677