Retirement Plans (Fair Value of Pension Plan Assets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 27, 2014	Dec. 28, 2013	Dec. 29, 2012
Retirement Plans [Line Items]
Fair value of plan assets	$ 267,635	$ 260,917
Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	267,635	260,917	231,897
Cash and cash equivalents [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	6,661	6,115
Equity [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	133,833	141,334
Fixed income [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	66,899	58,668
Other [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	1,599	1,684
Alternative investments [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	58,643	53,116
Level 1 [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	157,190	164,630
Level 1 [Member] | Cash and cash equivalents [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	6,661	6,115
Level 1 [Member] | Equity [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	133,833	141,334
Level 1 [Member] | Fixed income [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	16,696	17,181
Level 1 [Member] | Other [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Alternative investments [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	51,802	43,171
Level 2 [Member] | Cash and cash equivalents [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Equity [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Fixed income [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	50,203	41,487
Level 2 [Member] | Other [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	1,599	1,684
Level 2 [Member] | Alternative investments [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	58,643	53,116
Level 3 [Member] | Cash and cash equivalents [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Equity [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Fixed income [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Other [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Alternative investments [Member] | Pensions [Member]
Retirement Plans [Line Items]
Fair value of plan assets	$ 58,643	$ 53,116	$ 46,297