Retirement Benefits (Plan Assets by Category and Fair Value Measurement Level) (Details) - Pension Benefits - USD ($) $ in Thousands	Dec. 27, 2019	Dec. 28, 2018	Dec. 29, 2017
Defined Benefit Plan Disclosure [Line Items]
Investments, Fair Value Disclosure	$ 27,519	$ 27,291
Investments Net Asset Value	276,425	241,962
Fair value, plan assets	303,944	269,253	$ 254,186
Fair Value, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value, plan assets	303,944	269,253
Cash and cash equivalents | Level 1 | Fair Value, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments, Fair Value Disclosure	(156)	927
Insurance contract | Level 3 | Fair Value, Nonrecurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments, Fair Value Disclosure	27,675	26,364
Equity | Fair Value, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments Net Asset Value	132,772	92,785
U.S. Large Cap | Fair Value, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments Net Asset Value	84,330	53,597
U.S. Small/Mid Cap | Fair Value, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments Net Asset Value	9,202	7,602
International | Fair Value, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments Net Asset Value	39,240	31,586
Fixed income | Fair Value, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments Net Asset Value	107,832	76,213
Real estate and other | Fair Value, Recurring [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments Net Asset Value	$ 35,821	$ 72,964