Financial instruments - Fair values of derivative instruments designated as hedging instruments (Details) - USD ($) $ in Thousands	Sep. 26, 2021	Dec. 31, 2020
Cash flow hedging
Derivatives Fair Value [Line Items]
Total asset derivatives	$ 26,895	$ 21,858
Total liability derivatives	10,919	35,995
Foreign exchange contract | Other liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	9,946	34,125
Foreign exchange contract | Cash flow hedging | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	26,895	21,858
Foreign exchange contract | Cash flow hedging | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	973	1,870
Foreign exchange contract | Designated as Hedging Instrument | Cash flow hedging | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	1,151	1,691
Foreign exchange contract | Designated as Hedging Instrument | Cash flow hedging | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	687	1,504
Foreign exchange contract | Not Designated as Hedging Instrument | Cash flow hedging | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	60	61
Foreign exchange contract | Not Designated as Hedging Instrument | Cash flow hedging | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	286	366
Cross-currency interest rate swaps | Not Designated as Hedging Instrument | Cash flow hedging | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	25,684	20,106
Cross-currency interest rate swaps | Not Designated as Hedging Instrument | Cash flow hedging | Other liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	$ 9,946	$ 34,125