Retirement Benefits (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 29, 2017	Dec. 30, 2016	Dec. 25, 2015
Defined Contribution Plan
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	3.00%
Company contribution rate for employees not covered by DBP	1.50%
Company contributions to 401K	$ 7,800,000	$ 6,700,000	$ 6,300,000
Highest earnings years	5 years
Years preceding retirement	10 years
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	100.00%
Accumulated benefit obligation for all defined benefit plans	$ 361,000,000	360,000,000
Pension Plan - Blue Plan [Member] | Equity
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	54.00%
Pension Plan - Blue Plan [Member] | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	36.00%
Pension Plan - Blue Plan [Member] | Real Estate and Other
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	10.00%
Pension Plan - Gray Plan [Member] | Equity
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	38.00%
Pension Plan - Gray Plan [Member] | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	53.00%
Pension Plan - Gray Plan [Member] | Real Estate and Other
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocations	9.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	$ 43,539,000	6,817,000
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ (12,313,000)	(1,565,000)	(423,000)
Investments at Net Asset Value, Redemption Frequency	daily
Investments at Net Asset Value, Unfunded Commitments	$ 3,000,000	4,000,000
Expected company contributions to retirement plans in 2017	1,400,000
Postretirement Medical Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 0	$ 0	$ 0
Retirement medical plan limit on annual increase in company cost	3.00%
Expected company contributions to retirement plans in 2017	$ 1,300,000
Assumed health care trend rates
Effect of a one-percentage-point increase in the assumed health care cost trend rates	$ 0
Health care cost trend rate assumed for next year	6.50%
Ultimate health care cost trend rate	4.50%
Year that rate reaches ultimate trend rate	2038
Old Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	$ 42,000,000
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 12,000,000
Minimum | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Investments at Net Asset Value, Redemption Notice Period	10 days
Maximum | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Investments at Net Asset Value, Redemption Notice Period	60 days