Financial instruments - Fair values of derivative instruments designated as hedging instruments (Details) - Cash flow hedging - USD ($) $ in Thousands	Jun. 28, 2020	Dec. 31, 2019
Derivatives Fair Value [Line Items]
Total asset derivatives	$ 58,453	$ 36,492
Total liability derivatives	3,578	1,387
Other assets
Derivatives Fair Value [Line Items]
Total asset derivatives	35,701	13,066
Foreign exchange contract | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	22,752	23,426
Foreign exchange contract | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	3,578	1,387
Foreign exchange contract | Designated as Hedging Instrument | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	995	1,659
Foreign exchange contract | Designated as Hedging Instrument | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	3,391	1,285
Foreign exchange contract | Not Designated as Hedging Instrument | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	105	192
Foreign exchange contract | Not Designated as Hedging Instrument | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	187	102
Cross-currency interest rate swaps | Not Designated as Hedging Instrument | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	21,652	21,575
Cross-currency interest rate swaps | Not Designated as Hedging Instrument | Other assets
Derivatives Fair Value [Line Items]
Total asset derivatives	$ 35,701	$ 13,066