Other Postretirement Benefits - Changes in the Benefit Obligation and Plan Assets and Other Amounts (Details) - Other Postretirement Benefit Plans, Defined Benefit [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 27, 2015	Dec. 28, 2014	Dec. 29, 2013
Change in benefit obligation
Benefit obligation at beginning of year	$ 81,054	$ 100,932
Service cost	588	580	$ 1,089
Interest cost	2,794	3,722	4,101
Plan participants’ contributions	4,230	3,834
Actuarial (gain)/loss	(5,543)	12,091
Plan amendments	1,145	(25,489)
Benefits paid	(13,221)	(14,616)
Benefit obligation at end of year	71,047	81,054	100,932
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Employer contributions	8,991	10,782
Plan participants’ contributions	4,230	3,834
Benefits paid	(13,221)	(14,616)
Fair value of plan assets at end of year	0	0	$ 0
Amount recognized in the Consolidated Balance Sheets
Current liabilities	(8,168)	(9,426)
Noncurrent liabilities	(62,879)	(71,628)
Net amount recognized	(71,047)	(81,054)
Amount recognized in accumulated other comprehensive loss
Actuarial loss	26,599	37,339
Prior service cost	(41,309)	(51,950)
Total amount recognized in accumulated other comprehensive loss	$ (14,710)	$ (14,611)