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		9 Months Ended
	Sep. 26, 2021	Sep. 27, 2020	Sep. 26, 2021	Sep. 27, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange gains (losses)	$ (15,312)	$ 20,632	$ (33,307)	$ 20,087
Interest benefit			13,882	14,488
Cross-currency interest rate swaps | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange gains (losses)	8,873	(23,172)	19,360	(5,565)
Cross-currency interest rate swaps | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest benefit	$ 4,756	$ 4,684	$ 13,882	$ 14,488