Shareholders' equity - Change in accumulated other comprehensive income, net of tax (Details) - USD ($) $ in Thousands	3 Months Ended
Apr. 02, 2017	Mar. 27, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 2,137,517
Other comprehensive income (loss) before reclassifications	47,091	$ 20,608
Amounts reclassified from accumulated other comprehensive income	2,509	2,586
Net current-period other comprehensive income	49,600	23,194
Ending Balance	2,218,904
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(2,424)	(2,491)
Other comprehensive income (loss) before reclassifications	350	(50)
Amounts reclassified from accumulated other comprehensive income	1,378	1,530
Net current-period other comprehensive income	1,728	1,480
Ending Balance	(696)	(1,011)
Pension and Other Postretirement Benefit Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(136,596)	(138,887)
Other comprehensive income (loss) before reclassifications	(241)	182
Amounts reclassified from accumulated other comprehensive income	1,131	1,056
Net current-period other comprehensive income	890	1,238
Ending Balance	(135,706)	(137,649)
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(299,697)	(229,746)
Other comprehensive income (loss) before reclassifications	46,982	20,476
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive income	46,982	20,476
Ending Balance	(252,715)	(209,270)
Accumulated Other Comprehensive (Loss) Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(438,717)	(371,124)
Ending Balance	$ (389,117)	$ (347,930)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=66004921&loc=d3e1436-108581

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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669686-108580

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Amount of increase (decrease) in other comprehensive income, after tax, from changes classified as other.

+ References

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

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- Definition

Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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