Other Postretirement Benefits - Changes in the Benefit Obligations Recognized in Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 25, 2011	Dec. 26, 2010	Dec. 27, 2009
Other Postretirement Benefits
Additional postretirement costs	$ 16,000	$ 18,000	$ 18,000
Other Postretirement Benefit Plans, Defined Benefit [Member]
Other Postretirement Benefits
Net loss/(gain)	13,436	(16,865)	15,749
Prior service credit	(35,712)	0	(9,581)
Recognized actuarial loss	(2,289)	(3,129)	(2,014)
Amortization of prior service cost/(credit)	16,593	15,602	14,902
Total recognized in other comprehensive loss	(7,972)	(4,392)	19,056
Net periodic pension cost/(income)	(6,271)	(2,057)	(982)
Total recognized in net periodic benefit cost and other comprehensive loss	(14,243)	(6,449)	18,074
Estimated actuarial loss that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	3,000
Estimated prior service cost that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	$ 15,000