Postretirement Benefit Costs for Health Care and Life Insurance (Detail) (Other Postretirement Benefit Plans, Defined Benefit, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 30, 2012	Dec. 25, 2011	Dec. 26, 2010
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost-benefits earned during the period	$ 545	$ 611	$ 713
Interest cost on net benefit obligation	7,744	9,205	10,606
Amortization of prior service costs	(19,190)	(19,510)	(19,377)
Amortization of actuarial loss	1,943	5,444	4,949
Net periodic (benefit) cost	$ (8,958)	$ (4,250)	$ (3,109)