Shareholders' equity - Change in accumulated other comprehensive income, net of tax (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 3,073,024	$ 2,569,878	$ 2,979,320	$ 2,539,978
Amounts reclassified from accumulated other comprehensive income	759	1,242	2,128	2,430
Ending Balance	3,097,402	2,664,844	3,097,402	2,664,844
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			735	807
Other comprehensive (loss) income before reclassifications			(4,189)	429
Amounts reclassified from accumulated other comprehensive income			(723)	(271)
Net current-period other comprehensive (loss) income			(4,912)	158
Ending Balance	(4,177)	965	(4,177)	965
Pension and Other Postretirement Benefit Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(138,810)	(131,380)
Other comprehensive (loss) income before reclassifications			183	(13)
Amounts reclassified from accumulated other comprehensive income	1,425	1,350	2,851	2,701
Net current-period other comprehensive (loss) income			3,034	2,688
Ending Balance	(135,776)	(128,692)	(135,776)	(128,692)
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(206,317)	(210,512)
Other comprehensive (loss) income before reclassifications			(545)	12,332
Amounts reclassified from accumulated other comprehensive income			0	0
Net current-period other comprehensive (loss) income			(545)	12,332
Ending Balance	(206,862)	(198,180)	(206,862)	(198,180)
Accumulated Other Comprehensive (Loss) Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(364,719)	(340,689)	(344,392)	(341,085)
Other comprehensive (loss) income before reclassifications			(4,551)	12,748
Amounts reclassified from accumulated other comprehensive income			2,128	2,430
Net current-period other comprehensive (loss) income			(2,423)	15,178
Ending Balance	$ (346,815)	$ (325,907)	$ (346,815)	$ (325,907)