Changes in accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 02, 2021	Sep. 26, 2020	Oct. 02, 2021	Sep. 26, 2020
Accumulated Other Comprehensive Income [Roll Forward]
Beginning of Period			$ (488,428)	$ (350,933)
Other comprehensive income before reclassification			(28,468)	(32,675)
Amounts reclassified from accumulated other comprehensive income			14,691	10,419
Net current-period other comprehensive income			(13,777)	(22,256)
End of Period	$ (502,205)	$ (373,189)	(502,205)	(373,189)
Accumulated Other Comprehensive (income) Loss, Defined Benefit Plan, Tax	(88,400)	(47,300)	(88,400)	(47,300)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Tax	(7,500)	(15,300)	(7,500)	(15,300)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, Tax			700	1,300
Unrealized gain on interest rate swap, tax	1,065	960	5,637	(9,303)
Accumulated Translation Adjustment
Accumulated Other Comprehensive Income [Roll Forward]
Beginning of Period			(49,961)	(105,705)
Other comprehensive income before reclassification			(33,000)	(3,213)
Amounts reclassified from accumulated other comprehensive income			0	0
Net current-period other comprehensive income			(33,000)	(3,213)
End of Period	(82,961)	(108,918)	(82,961)	(108,918)
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income [Roll Forward]
Beginning of Period			(400,919)	(228,336)
Other comprehensive income before reclassification			(3,052)	(6,184)
Amounts reclassified from accumulated other comprehensive income			0	0
Net current-period other comprehensive income			3,052	6,184
End of Period	(397,867)	(222,152)	(397,867)	(222,152)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent | Interest Rate Swap
Accumulated Other Comprehensive Income [Roll Forward]
Beginning of Period			(37,548)	(16,892)
Other comprehensive income before reclassification			1,480	(35,646)
Amounts reclassified from accumulated other comprehensive income			14,691	10,419
Net current-period other comprehensive income			16,171	(25,227)
End of Period	$ (21,377)	$ (42,119)	$ (21,377)	$ (42,119)