Financial instruments - Fair values of derivative instruments designated as hedging instruments (Details) - Cash flow hedging - USD ($) $ in Thousands	Sep. 27, 2020	Dec. 31, 2019
Derivatives Fair Value [Line Items]
Total asset derivatives	$ 32,906	$ 36,492
Total liability derivatives	2,672	1,387
Other assets
Derivatives Fair Value [Line Items]
Total asset derivatives	6,113	13,066
Foreign exchange contract | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	26,793	23,426
Foreign exchange contract | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	2,672	1,387
Foreign exchange contract | Designated as Hedging Instrument | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	916	1,659
Foreign exchange contract | Designated as Hedging Instrument | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	2,449	1,285
Foreign exchange contract | Not Designated as Hedging Instrument | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Total asset derivatives	81	192
Foreign exchange contract | Not Designated as Hedging Instrument | Other current liabilities
Derivatives Fair Value [Line Items]
Total liability derivatives	223	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	25,796	21,575
Cross-currency interest rate swaps | Not Designated as Hedging Instrument | Other assets
Derivatives Fair Value [Line Items]
Total asset derivatives	$ 6,113	$ 13,066