Pension Benefits - Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 25, 2016	Dec. 27, 2015	Dec. 28, 2014
Pension Benefits
Defined contribution plan, cost recognized	$ 15,000	$ 16,000	$ 17,000
Pension Plan [Member]
Pension Benefits
Net actuarial loss/(gain)	(4,289)	31,044	254,525
Amortization of loss	(32,458)	(41,523)	(30,665)
Amortization of prior service cost	1,945	1,945	1,945
Effect of curtailment	0	(1,264)	0
Effect of settlement	(21,294)	(40,329)	(9,525)
Total recognized in other comprehensive (income)/loss	(56,096)	(50,127)	216,280
Net periodic pension cost	22,648	61,331	29,703
Total recognized in net periodic benefit cost and other comprehensive loss	(33,448)	$ 11,204	$ 245,983
Estimated actuarial loss that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	34,000
Estimated prior service credit that will be amortized from accumulated other comprehensive loss into net periodic pension cost over the next fiscal year	$ 2,000