Financial instruments - Foreign exchange gains and losses recognized within AOCI and the interest benefit recognized within interest expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 27, 2021	Jun. 28, 2020	Jun. 27, 2021	Jun. 28, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange (losses) gains	$ 6,080	$ 17,654	$ (17,995)	$ (545)
Interest benefit			9,126	9,805
Cross-currency interest rate swaps \| Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange (losses) gains	(7,127)	(7,408)	10,487	17,607
Cross-currency interest rate swaps \| Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest benefit	$ 4,479	$ 4,931	$ 9,126	$ 9,805

Amount after tax, before 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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 35
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=123602790&loc=d3e30304-110892

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 10
-Section 45
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=120253306&loc=d3e28129-110885

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32022-110900

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (a-c)
-URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=124509347&loc=d3e637-108580

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration