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, unless otherwise specified	12 Months Ended
	Dec. 30, 2012	Dec. 25, 2011	Dec. 26, 2010
Other Postretirement Benefit Plans, Defined Benefit [Member]
Change in benefit obligation
Benefit obligation at beginning of year	$ 113,803	$ 142,417
Service cost	957	1,143	1,076
Interest cost	4,985	6,890	9,340
Plan participants’ contributions	4,383	4,659
Actuarial loss	11,562	13,436
Plan amendments	0	(35,712)
Benefits paid	(15,881)	(20,247)
Medicare subsidies received	957	1,217
Benefit obligation at end of year	120,766	113,803	142,417
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	0	0
Employer contributions	10,541	14,371
Fair value of plan assets at end of year	0	0	0
Current liabilities	(10,419)	(9,611)
Noncurrent liabilities	(110,347)	(104,192)
Net amount recognized	(120,766)	(113,803)
Actuarial loss	51,348	43,114
Prior service cost	(94,144)	(136,469)
Total amount recognized in accumulated other comprehensive loss	$ (42,796)	$ (93,355)