Other Postretirement Benefits - Changes in the Benefit Obligation and Plan Assets and Other Amounts (Details) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Change in benefit obligation
Benefit obligation at beginning of year	$ 54,642	$ 65,042
Service cost	21	367	$ 417
Interest cost	1,476	1,881	1,979
Plan participants’ contributions	3,974	4,007
Actuarial (gain)/loss	(4,905)	3,703
Curtailments/settlements	0	(10,328)
Benefits paid	(9,171)	(10,030)
Benefit obligation at end of year	46,037	54,642	65,042
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Employer contributions	5,197	6,023
Plan participants’ contributions	3,974	4,007
Benefits paid	(9,171)	(10,030)
Fair value of plan assets at end of year	0	0	$ 0
Amount recognized in the Consolidated Balance Sheets
Current liabilities	(5,645)	(5,826)
Noncurrent liabilities	(40,392)	(48,816)
Net amount recognized	(46,037)	(54,642)
Amount recognized in accumulated other comprehensive loss
Actuarial loss	28,871	38,512
Prior service credit	(12,456)	(18,613)
Total	$ 16,415	$ 19,899