Accumulated other comprehensive loss (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 26, 2014	Dec. 27, 2013
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Defined Benefit Plan Adjustments, Beginning Balance	$ (4,176)	$ (4,133)
Adjustments to defined benefit plans	(1,205)	(43)
Defined Benefit Plan Adjustments, Ending Balance	(5,381)	(4,176)
Currency Translation Adjustments, Beginning Balance	25,226	24,824
Currency Translation Adjustments	717	402
Currency Translation Adjustments, Ending Balance	25,943	25,226
Unrealized Holding Losses on Securities, Beginning Balance	7	12
Unrealized Holding Losses on Securities	0	(5)
Unrealized Holding Losses on Securities, Ending Balance	7	7
Total, Beginning Balance	21,057	20,703
Total, Current Year Changes	(488)	354
Total, Ending Balance	$ 20,569	$ 21,057

Accumulated appreciation or loss, net of tax, in value of the total of available-for-sale securities at the end of an accounting period.

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The total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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