Pension Benefits - Fair Value of Plan Assets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 30, 2012		Dec. 25, 2011		Dec. 26, 2010
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	$ 280,762		$ 248,414
Fair Value, Inputs, Level 1 [Member] | U.S. Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	193,489		173,988
Fair Value, Inputs, Level 1 [Member] | International Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	87,273		74,426
Fair Value, Inputs, Level 1 [Member] | Common Collective Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0	[1]	0	[1]
Fair Value, Inputs, Level 1 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 1 [Member] | Insurance Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 1 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0	[2]	0	[2]
Fair Value, Inputs, Level 1 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 1 [Member] | Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 1 [Member] | Hedge Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	1,266,146		1,173,565
Fair Value, Inputs, Level 2 [Member] | U.S. Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 2 [Member] | International Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 2 [Member] | Common Collective Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	678,449	[1]	714,300	[1]
Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	383,483		266,510
Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	91,122		98,531
Fair Value, Inputs, Level 2 [Member] | Insurance Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	44,511		31,847
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	22,192		16,850
Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	19,115	[2]	15,394	[2]
Fair Value, Inputs, Level 2 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	10,847		7,268
Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	16,427		22,865
Fair Value, Inputs, Level 2 [Member] | Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	62,381		37,393		68,658
Fair Value, Inputs, Level 3 [Member] | U.S. Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 3 [Member] | International Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 3 [Member] | Common Collective Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0	[1]	0	[1]
Fair Value, Inputs, Level 3 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 3 [Member] | Insurance Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 3 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0	[2]	0	[2]
Fair Value, Inputs, Level 3 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Fair Value, Inputs, Level 3 [Member] | Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	36,011		37,393		31,187
Fair Value, Inputs, Level 3 [Member] | Hedge Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	26,370		0
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	1,609,289		1,459,372
Fair value of plan assets	1,615,723		1,464,729
Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	193,489		173,988
Estimate of Fair Value, Fair Value Disclosure [Member] | International Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	87,273		74,426
Estimate of Fair Value, Fair Value Disclosure [Member] | Common Collective Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	678,449	[1]	714,300	[1]
Estimate of Fair Value, Fair Value Disclosure [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	383,483		266,510
Estimate of Fair Value, Fair Value Disclosure [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	91,122		98,531
Estimate of Fair Value, Fair Value Disclosure [Member] | Insurance Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	44,511		31,847
Estimate of Fair Value, Fair Value Disclosure [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	22,192		16,850
Estimate of Fair Value, Fair Value Disclosure [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	19,115	[2]	15,394	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	10,847		7,268
Estimate of Fair Value, Fair Value Disclosure [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	16,427		22,865
Estimate of Fair Value, Fair Value Disclosure [Member] | Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	36,011		37,393
Estimate of Fair Value, Fair Value Disclosure [Member] | Hedge Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	26,370
Estimate of Fair Value, Fair Value Disclosure [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	$ 6,434		$ 5,357

[1] The underlying assets of the common/collective funds are primarily comprised of equity and fixed income securities. The fair value in the above table represents our ownership share of the net asset value of the underlying funds.

[2] Represents investments that are not backed by the full faith and credit of the United States government.