Shareholders' Equity Shareholders' Equity (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 27, 2017	Dec. 28, 2016	Dec. 30, 2015
AOCI Attributable To Parent, Net Of Tax [Roll Forward]
Accumulated other comprehensive loss, net of tax, beginning balance		$ (1,407)	$ (23,777)	$ (24,602)
Benefit obligation actuarial gain (loss)		(172)	(1,018)	5,737
Net gain (loss)			603	(3,894)
Amortization of net loss	[1]	92	85	1,812
Settlement loss recognized		21	24,297
Net change in fair value of derivatives		(1,359)	1,693	(1,444)
Reclassification of derivatives to interest expense	[2]	(72)	(789)	(859)
Income tax benefit (expense)		581	(2,501)	(527)
Accumulated other comprehensive loss, net of tax, ending balance		(2,316)	(1,407)	(23,777)
Estimated reclassification from other comprehensive income to interest expense related to the interest rate swaps over the next 12 months		1,300
Pensions [Member]
AOCI Attributable To Parent, Net Of Tax [Roll Forward]
Accumulated other comprehensive loss, net of tax, beginning balance		(945)	(22,764)	(24,994)
Benefit obligation actuarial gain (loss)		(172)	(1,018)	5,737
Net gain (loss)			603	(3,894)
Amortization of net loss	[1]	92	85	1,812
Settlement loss recognized		21	24,297
Income tax benefit (expense)		22	(2,148)	(1,425)
Accumulated other comprehensive loss, net of tax, ending balance		(982)	(945)	(22,764)
Derivatives [Member]
AOCI Attributable To Parent, Net Of Tax [Roll Forward]
Accumulated other comprehensive loss, net of tax, beginning balance		(462)	(1,013)	392
Net change in fair value of derivatives		(1,359)	1,693	(1,444)
Reclassification of derivatives to interest expense	[2]	(72)	(789)	(859)
Income tax benefit (expense)		559	(353)	898
Accumulated other comprehensive loss, net of tax, ending balance		$ (1,334)	$ (462)	$ (1,013)

[1] Before-tax amount that was reclassified from accumulated other comprehensive loss and included as a component of pension expense within general and administrative expenses in our Consolidated Statements of Income. See Note 11 for additional details.

[2] Amounts reclassified from accumulated other comprehensive loss into income, represent payments made to the counterparty for the effective portions of the interest rate swaps. These amounts are included as a component of interest expense in our Consolidated Statements of Income. We expect to reclassify approximately $1.3 million from accumulated other comprehensive loss related to our interest rate swaps during the next twelve months. See Note 10 for additional details.