Retirement Benefits (Plan assets by category and fair value measurement level) (Details) - USD ($) $ in Thousands	Dec. 25, 2015	Dec. 26, 2014	Dec. 27, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	$ 268,258	$ 277,208
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	6,578	1,356
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	193,281	208,879
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	68,399	66,973	$ 25,844
U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	77,811	92,272
U.S. Large Cap | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
U.S. Large Cap | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	77,811	92,272
U.S. Large Cap | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
U.S. Small/Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	12,759	14,948
U.S. Small/Mid Cap | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
U.S. Small/Mid Cap | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	12,759	14,948
U.S. Small/Mid Cap | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
International
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	49,952	45,958
International | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
International | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	49,952	45,958
International | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	140,522	153,178
Equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
Equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	140,522	153,178
Equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	42,251	53,548
Fixed income | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
Fixed income | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	36,711	40,693
Fixed income | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	5,540	12,855
Insurance contract
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	28,080	28,899
Insurance contract | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
Insurance contract | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	0	0
Insurance contract | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	28,080	28,899
Real estate and other
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	57,405	41,583
Real estate and other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	6,578	1,356
Real estate and other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	16,048	15,008
Real estate and other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	$ 34,779	$ 25,219