Components of accumulated other comprehensive loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 25, 2014	Jun. 26, 2013	Jun. 25, 2014		Jun. 26, 2013
Components of Change in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 25, 2013			$ (16,842)
Amortization of net loss, before tax			462	[1]
Net change in fair value of derivatives, before tax			(1,440)
Unrealized gain (loss) on hedged transactions, tax expense (benefit)	339	(1,522)	563		(1,522)
Other comprehensive loss, tax benefit			382
Balance as of June 25, 2014	(17,438)		(17,438)
Pensions [Member]
Components of Change in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 25, 2013			(18,690)
Amortization of net loss, before tax			462	[1]
Minimum pension liability, adjustment, tax expense			(181)
Balance as of June 25, 2014	(18,409)		(18,409)
Derivatives [Member]
Components of Change in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 25, 2013			1,848
Net change in fair value of derivatives, before tax			(1,440)
Unrealized gain (loss) on hedged transactions, tax expense (benefit)			563
Balance as of June 25, 2014	$ 971		$ 971

[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 Condensed Consolidated Statements of Income during the two quarters ended June 25, 2014. See Note 8 for additional details.