Shareholders' equity - Change in accumulated other comprehensive income, net of tax (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 2,569,878	$ 2,561,466	$ 2,539,978	$ 2,430,531
Amounts reclassified from accumulated other comprehensive income	(2,564)	1,258	(4,329)	1,897
Ending Balance	2,664,844	2,433,981	2,664,844	2,433,981
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			807	340
Other comprehensive income (loss) before reclassifications			429	1,103
Amounts reclassified from accumulated other comprehensive income			(271)	(811)
Net current-period other comprehensive income (loss)			158	292
Ending Balance	965	632	965	632
Pension and Other Postretirement Benefit Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(131,380)	(138,808)
Other comprehensive income (loss) before reclassifications			(13)	188
Amounts reclassified from accumulated other comprehensive income	1,350	1,349	2,701	2,708
Net current-period other comprehensive income (loss)			2,688	2,896
Ending Balance	(128,692)	(135,912)	(128,692)	(135,912)
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(210,512)	(126,623)
Other comprehensive income (loss) before reclassifications			12,332	(44,517)
Amounts reclassified from accumulated other comprehensive income			0	0
Net current-period other comprehensive income (loss)			12,332	(44,517)
Ending Balance	(198,180)	(171,140)	(198,180)	(171,140)
Accumulated Other Comprehensive (Loss) Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(340,689)	(182,401)	(341,085)	(265,091)
Other comprehensive income (loss) before reclassifications			12,748	(43,226)
Amounts reclassified from accumulated other comprehensive income			2,430	1,897
Net current-period other comprehensive income (loss)			15,178	(41,329)
Ending Balance	$ (325,907)	$ (306,420)	$ (325,907)	$ (306,420)

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount of increase (decrease) in other comprehensive income, after tax, from changes classified as other.

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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