Retirement Benefits (Amounts recognized in other comprehensive (income) loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 25, 2015	Dec. 26, 2014	Dec. 27, 2013
Amounts recognized in other comprehensive (income) loss
Total	$ (10,372)	$ 39,164	$ (46,955)
Pension Benefits
Amounts recognized in other comprehensive (income) loss
Net loss (gain) arising during the period	(833)	42,733
Prior service cost (credit) arising during the period	(179)	0
Amortization of net gain (loss)	(9,459)	(4,929)
Amortization of prior service credit (cost)	(268)	(320)
Total	(10,739)	37,484
Postretirement Medical Benefits
Amounts recognized in other comprehensive (income) loss
Net loss (gain) arising during the period	14	1,037
Prior service cost (credit) arising during the period	0	0
Amortization of net gain (loss)	(323)	(15)
Amortization of prior service credit (cost)	676	658
Total	$ 367	$ 1,680