Pension Benefits - Fair Value of Plan Assets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 28, 2014		Dec. 29, 2013		Dec. 30, 2012
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	$ 99,846		$ 112,526
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	48,640		36,920
Level 1 [Member] | International Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	51,154		75,606
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]
Level 1 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 1 [Member] | US Treasury and Other Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 1 [Member] | Group Annuity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 1 [Member] | Municipal and Provincial Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 1 [Member] | US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0	[2]	0	[2]
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
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	52		0
Level 1 [Member] | Private Equity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 1 [Member] | Hedge Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	1,670,383		1,514,703
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
Level 2 [Member] | International Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
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	697,075	[1]	581,553	[1]
Level 2 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	539,098		594,667
Level 2 [Member] | US Treasury and Other Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	150,496		183,700
Level 2 [Member] | Group Annuity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	76,290		72,663
Level 2 [Member] | Municipal and Provincial Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	47,046		41,729
Level 2 [Member] | US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	9,517	[2]	4,738	[2]
Level 2 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	22,951		29,115
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	127,910		6,538
Level 2 [Member] | Private Equity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 2 [Member] | Hedge Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	67,021		70,862		62,381
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
Level 3 [Member] | International Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
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]
Level 3 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 3 [Member] | US Treasury and Other Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 3 [Member] | Group Annuity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 3 [Member] | Municipal and Provincial Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0		0
Level 3 [Member] | US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	0	[2]	0	[2]
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
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
Level 3 [Member] | Private Equity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	35,727		40,537		36,011
Level 3 [Member] | Hedge Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	31,294		30,325
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	1,837,250		1,698,091
Estimate of Fair Value Measurement [Member] | U.S. Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	48,640		36,920
Estimate of Fair Value Measurement [Member] | International Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	51,154		75,606
Estimate of Fair Value Measurement [Member] | Common Collective Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	697,075	[1]	581,553	[1]
Estimate of Fair Value Measurement [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	539,098		594,667
Estimate of Fair Value Measurement [Member] | US Treasury and Other Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	150,496		183,700
Estimate of Fair Value Measurement [Member] | Group Annuity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	76,290		72,663
Estimate of Fair Value Measurement [Member] | Municipal and Provincial Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	47,046		41,729
Estimate of Fair Value Measurement [Member] | US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	9,517	[2]	4,738	[2]
Estimate of Fair Value Measurement [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	22,951		29,115
Estimate of Fair Value Measurement [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	127,962		6,538
Estimate of Fair Value Measurement [Member] | Private Equity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	35,727		40,537
Estimate of Fair Value Measurement [Member] | Hedge Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, recurring	$ 31,294		$ 30,325

[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.